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On ogeny o he ci cadian sys em: A mul iscale p ocess h oughou de elopmen
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Ma ia Comas1, Da ide De Pie i Tonelli2, Luca Be dondini3 and Ma iana As iz1,4,5*
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1Ci cadian Physiology o Neu ons and Glia Labo a o y, Achuca o Basque Cen e o
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Neu oscience, 48940 Leioa, Basque Coun y, Spain.
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2Neu obiology o miRNA, Fondazione Is i u o I aliano di Tecnologia (IIT), 16163 Geno a, I aly.
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3Mic o echnology o Neu oelec onics, Fondazione Is i u o I aliano di Tecnologia (IIT), 16163
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Geno a, I aly.
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4IKERBASQUE, Basque Founda ion o Science, Bilbao, Spain.
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5Ins i u e o Neu obiology, Uni e si y o Lübeck, 23562 Lübeck, Ge many.
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*Co espondence: Ma iana As iz, PhD. Ci cadian Physiology o Neu ons and Glia Labo a o y,
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Achuca o Basque Cen e o Neu oscience, 48940 Leioa, Basque Coun y, Spain. Email:
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ma iana.as iz@achuca o.o g. Tel: +34 946018160
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Keywo ds: ci cadian clock, mouse, humans, sup achiasma ic nuclei, as ocy es, neu ons
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Abs ac :
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The 24 h (ci cadian) iming sys em de elops in mammals du ing he pe ina al pe iod. I ca ies
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ou he essen ial ask o an icipa ing daily ecu ing en i onmen al changes o iden i y he
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bes ime o day o each molecula , cellula and sys emic p ocess. While signi ican knowledge
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has been acqui ed abou he o ganiza ion and unc ion o he adul ci cadian sys em, ela i ely
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li le is known abou i s on ogeny. Du ing he pe ina al pe iod, he ci cadian sys em
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p og essi ely gains unc ionali y unde he in luence o he ea ly en i onmen . This e iew
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explo es cu en e idence on he de elopmen o he ci cadian clock in mammals, highligh ing
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he mul i-le el complexi y o he p ocess and he impo ance o gaining be e unde s anding
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o i s unde lying biology.
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The eme gence o he mammalian ci cadian sys em
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Li e on Ea h has e ol ed unde he in luence o geophysical cycles ha gene a e ecu en
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en i onmen al changes wi h s able pe iods. The diu nal oscilla ions (see glossa y) o ligh
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in ensi y and empe a u e, as a esul o he Ea h o a ing a ound i s axis, ha e a pe iod o 24
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hou s (h) and in luence e e y o ganism’s physiology. These oscilla ions a e e icien ly
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an icipa ed by he ci cadian sys em, which is necessa y o o ganizing sleep-wake cycles and
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mos physiological hy hms o ma ch he 24 h en i onmen al pe iod ( he e m ci cadian
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de i es om he La in wo ds ci ca – app oxima ely, and dies – day) ( e iewed in [1]). The
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ci cadian sys em can be concep ualized as a h ee-componen sys em: i equi es inpu
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pa hways p o iding empo al in o ma ion o an “en ainable” (bu sel -sus ained) oscilla o
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which is, in u n, able o p oduce he hy hmic ou pu necessa y o synch onize di e en
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p ocesses. In mul icellula o ganisms his h ee-componen sys em can be ound a h ee
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le els: molecula , issue/ci cui and sys emic [2].
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Compa ed wi h he knowledge ha has been acqui ed on he adul ci cadian sys em, i s
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on ogeny is no well unde s ood. The mammalian ci cadian sys em gains unc ionali y
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p og essi ely unde he dynamic in luence o he pe ina al en i onmen ( e iewed in [3]). In
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bo h oden s and humans, he pe ina al pe iod is conside ed he c i ical window when he
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de elopmen and ma u a ion o he sys em akes place. While in humans mos hypo halamic
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nuclei, including he mas e clock in he sup achiasma ic nuclei (SCN), a e ma u e by he end
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o ges a ion, in oden s his p ocess con inues a e bi h ( e iewed in [4]).
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Wi h a b ie in oduc ion on how he ci cadian sys em is o ganized in adul s, his e iew
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ocuses on cu en e idence on he on ogeny o he mas e clock in mammals a he
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molecula , ci cui and sys emic le el. We highligh some o he less explo ed aspec s o his
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complex p ocess and discuss he need o be e unde s anding he in luence o an ad e se
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pe ina al en i onmen la e in li e.
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How is he adul ci cadian sys em o ganized?
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Ci cadian hy hms in mammals a e coo dina ed a sys emic le el by he mas e pacemake in
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he SCN, loca ed on each side o he hi d en icle (3V) and abo e he op ic chiasm (OC). Ligh
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signals a e ecei ed by he e ina and ansmi ed h ough neu onal pa hways o he SCN,
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hus, en aining he oscilla o o he 24 h ligh -da k cycle [5,6]. In absence o ligh inpu , he
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oscilla o main ains sel -sus ained hy hms, wi h a pe iod ha app oxima es 24 h (τ) [7–9].
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The abili y o he SCN o synch onize hy hms sys emically, elies on ex ensi e neu onal
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p ojec ions and pa ac ine communica ion. These pa hways each di e en b ain a eas
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including he medial hypo halamus coo dina ing ho mone elease and he one o he
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au onomic ne ous sys em [10]. Two well-known examples o ho monal ou pu s a e he
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sec e ions o mela onin (du ing he da k phase) and glucoco icoids (GCs, be o e he ac i e
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phase) [11–13]. The SCN has been iden i ied as he mas e ci cadian pacemake by lesion
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expe imen s. SCN-lesioned a s showed a hy hmic beha io , e idenced by an al e ed pa e n
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o locomo o ac i i y, dis up ed sleep-wake and eeding- as ing cycles and loss o ci cadian
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ho monal le els [7,14]. The sys emic hy hmici y can be es o ed by ansplan ing a g a
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con aining SCN in he lesion si e, e en i he g a is w apped in a mesh blocking e e en
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ou g ow h, e idencing he ele ance o pa ac ine ou pu signals [15,16]. These key
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disco e ies, we e ollowed by he cha ac e iza ion o neu onal popula ions, coupling
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mechanisms be ween neighbo ing cells wi hin he ci cui , and he synap ic and pa ac ine
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signalling pa hways ha keep he ime.
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The mas e clock ci cui in adul oden s is o med by ew housands GABAe gic neu ons
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highly in e connec ed, exhibi ing p ecise and high ampli ude ci cadian cycles o gene
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exp ession, me abolic and elec ical ac i i y ha pe sis au onomously in absence o ligh and
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when cul u ed in i o [17]. Topologically, he SCN is di ided in o a en al co e and a do sal
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shell. Neu ons om he co e ecei e glu ama e gic inne a ion om he e ina and p opaga e
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hei ac i a ion o he su ounding shell by eleasing mainly gamma-aminobu y ic acid (GABA)
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and asoac i e in es inal polypep ide (Vip). Shell neu ons, which in absence o ligh show
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au onomous ime-keepe ac i i y wi h a pe iod ~24 h, a e hen en ained and ans e hei
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synch ony o downs eam clocks h ough e e en connec ions eleasing asop essin (A p),
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GABA and o he signals ( e iewed in [18]). Pa ac ine communica ion wi hin he SCN ci cui is
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media ed by an he e ogenous a ay o hund eds o neu opep ides (e.g. gas in- eleasing
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pep ide (G p), neu omedin-S (Nms), among o he s) which a e belie ed o con e he ne wo k-
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le el p ope ies necessa y o main ain highly obus oscilla ions e en in absence o
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en i onmen al inpu [19]. This adi ional neu on-cen ic iew o he ci cui has changed o e
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ime, wi h demons a ions in oden s ha as ocy es a e compe en ci cadian oscilla o s,
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being able o modula e he clockwo k o o he cell ypes ([20–22], e iewed in [23]). In mice,
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he as ocy es’ clock is su icien and pa ially necessa y o d i e neu onal ci cadian hy hms
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in he SCN, e y likely con ibu ing o he highly obus oscilla ions o he ci cui [24–28]. In
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ligh o his e idence, he cu en iew on he adul SCN assumes a igh neu on-as ocy e
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in e ac ion, modula ing pa ac ine and synap ic communica ion o main ain he ci cui -le el
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p ope ies o he oscilla o and long- ange o ganiza ion o he ou pu wi hin and ou side he
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SCN ( e iewed in [29]). As in he SCN, mos o he issues/ci cui s show coupled oscilla ions
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be ween neighbo ing cells, al hough hey end o lose synch ony in absence o iming cues.
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The weake coupling o ex a-SCN issues and he inpu -dependen synch ony seems o be
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essen ial o he op- o-bo om coo dina ion o issue-speci ic ci cadian unc ions ( e iewed
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in [30]).
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The molecula clock, which is p esen in i ually all he cells, is he hi d le el o o ganiza ion
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o he ci cadian sys em. A se o co e clock p o eins (e.g., BMAL1, CLOCK, PER1-3, CRY1-2,
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RORα, REV-ERBα/β) gene a e sel -sus ained oscilla ions ha can be en ained by inpu signals.
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As a esul , in e locked au o- egula o y ansc ip ion- ansla ion eedback loops (TTFLs)
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p oduce molecula hy hms o abou 24 h ( e iewed in [31]). The TTFL egula es he hy hmic
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exp ession o he so called “clock-con olled genes” (CCG) which ep esen , depending on he
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cell ype, be ween 10-40% o he ansc ip ome ( e iewed in [32]). In addi ion, pos -
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ansc ip ional, ansla ional and pos - ansla ional p ocesses (including splicing,
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polyadenyla ion, RNA binding p o eins, mic oRNAs and o he epigene ic and
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epi ansc ip omic mechanisms) we e ound o play a ole in shaping he hy hmici y o
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mRNAs, and in he accumula ion o clock p o eins [33–35]. The cu en knowledge on hese
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mechanisms is mo e limi ed.
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Wha de ines a unc ional ci cadian clock?
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The ma u e ci cadian sys em depends on i s mul ile el na u e (i.e.: molecula , cellula and
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sys emic) and on he in eg a ion o he h ee componen s: inpu , oscilla o and ou pu (Figu e
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1). Du ing de elopmen , he mammalian clock s a s gaining unc ion in u e o and i ma u es
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comple ely a e bi h ( e iewed in [36–40]). Unde s anding his p ocess in i s complexi y is
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impe a i e, especially because du ing he las decade, s udies ha e e ealed an associa ion
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be ween ci cadian dis up ion du ing p egnancy/ea ly pos na al li e and poo
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neu ode elopmen al ou comes in animal models and humans ([41-46], e iewed in [47]). To
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unde s and he on ogeny o he ci cadian sys em, wo c i ical no ions o conside a e: ha he
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unc ional clock is de ined as “en ainable” and as able o main ain sel -sus ained hy hms.
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This implies ha he empo al inpu pa hways ha e o espond o ime cues and synch onize
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o “en ain” he oscilla o wi h a 24 h pe iod (T). Fu he mo e, in he absence o
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en i onmen al cues, he oscilla o mus ha e he abili y o gene a e sel -sus ained hy hms
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ha app oxima e a 24 h pe iod (τ). Las ly, he mul iple ou pu pa hways mus p oduce signals
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wi h a s able phase ela ionship, o phase angle, be ween he inpu and he oscilla o o
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ensu e p ope sys emic synch oniza ion.
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Ci cadian hy hms a e he e o e inna e. Wha emains unclea is when, du ing he p ocess o
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on ogeny, he ci cadian sys em s a s o ick in an in eg a ed and mul iscale manne and wha
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is he in luence o he ea ly en i onmen shaping he gain o unc ion. The main expe imen al
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di icul y has been o dissec whe he an oscilla ion is d i en by an en ainmen synch onizing
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signal (e.g. ma e nal hy hmic ho mones eaching e al/newbo n issues) o whe he i is sel -
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sus ained and au onomously gene a ed (e.g. by he e al/newbo n clock). Mo eo e , li le is
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known abou how he ma u a ion p ocess is coo dina ed du ing he pe ina al pe iod and how
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miles one/sequen ial e en s lead o he g adual gain o unc ionali y. Cu en e idence in
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oden s and humans shows ha he en i onmen o which he sys em is exposed o du ing
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de elopmen is c i ical o de ining i s unc ionali y la e on. The eby, he unc ional
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ma u a ion o he ci cadian sys em esul s om a complex and likely dynamic in e ac ion
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be ween exogenous (i.e.: ma e nal/ea ly en i onmen signals) and endogenous ac o s (i.e.:
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in insic molecula p og ams) ( e iewed in [38], [47]). In he ollowing sec ions we explo e he
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cu en knowledge on he ma u a ion o he ci cadian sys em a all h ee le els, and discuss
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cu en knowledge gaps.
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The ma u a ion o he molecula clock
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Du ing mammalian emb yonic de elopmen p ogeni o cells unde go p ecise a e decisions
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o become unc ionally ma u e. Ci cadian oscilla ions in he exp ession o he clockwo k genes
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appea o be absen in plu ipo en s em cells (ei he emb yonic o induced) [48]. Rhy hmic
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clock gene exp ession a ises p og essi ely and gains ampli ude as he cell a e becomes mo e
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de ined, sugges ing a igh coupling be ween he de elopmen o a unc ional molecula clock
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and he cellula di e en ia ion s a es ([49], e iewed in [50]). Pos - ansc ip ional supp ession
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o CLOCK p o ein has been iden i ied as one o he mechanisms se ing he ime o he
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molecula clock o s a icking [51]. Howe e , cell di e en ia ion depends on gene ic and
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epigene ic de e minan s modula ing whole egula o y ne wo ks ha speci ically de ine he
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a e o each cell. The e o e, i seems plausible ha mul iple gene-modula o y mechanisms
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(pos ansc ip ional [52,53], ansla ional [54] and pos ansla ional [34,35,55] ha a e jus
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s a ing o be explo ed, play a ole in his complex de elopmen al p ocess ( e iewed in [56]).
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As an example o he in icacy o hese mechanisms, we highligh a link be ween genomic
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imp in ing, mic oRNAs, and ligh -expe ience du ing he c i ical pe iod o he isual sys em
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de elopmen in mice [57]. In e es ingly, he majo i y o he imp in ed miRNAs ound, se e al
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o which a e known o con ol neu al s em cell a e [58,59], we e p edominan ly clus e ed in o
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he Dlk1-Dio3 locus, a genomic egion ha is associa ed wi h neu onal plas ici y and se e al
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neu ode elopmen al diso de s ( e iewed in [60]). Hence, pos - ansc ip ional/ ansla ional
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mechanisms in he con ex o ci cadian on ogeny a e o in e es o u u e in es iga ions. In
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mammals, howe e , hese mechanisms we e mos ly s udied in pe iphe al o gans, such as li e
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and in es ine [61], and he con ibu ion o hese mechanisms in di e en egions o he b ain,
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o in neu al cell subpopula ions, emains la gely unknown.
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In he mouse emb yo, he hy hmic exp ession o clock genes has been de ec ed qui e ea ly,
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a abou wo- hi ds o he in-u e o de elopmen (13 days o ges a ion) [62–65]. In he
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hypo halamus, his de elopmen al s age is compa able o he end o he hi d imes e in
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humans [4]. Howe e , i is possible ha hese hy hms a e no sel -sus ained and only induced
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by ma e nal en ainmen signals in i o o by he cul u e condi ions in i o. Se e al ma e nal
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signals such as mela onin [66], dopamine [67,68] and glucoco icoids [41,69] a e essen ial o
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p omo ing e al g ow h and issue ma u a ion as well as o communica ing ime. All h ee a e
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p oduced in a ci cadian manne and a e able o c oss he placen a and each e al issues ([70],
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e iewed in [38,71]). In e es ingly, ma e nal SCN lesions in a s o expe imen s in mice done
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wi h clock de icien dams (Pe 1/Pe 2 double knockou s) ha e shown ha du ing p egnancy,
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he absence o ma e nal clock educes he synch ony o e al hy hms likely due o low
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en ainmen by ma e nal hy hmic signals [72,73]. Howe e , he de elopmen o ci cadian
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hy hms in pups is no impai ed, sugges ing a ce ain deg ee o e al/newbo n clock au onomy
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du ing de elopmen [74]. Indeed, i has been demons a ed in mice ha he molecula clock
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in he e us, al eady a 15 days o ges a ion, is able o ga e he sensi i i y o he e al
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hypo halamus o ma e nal glucoco icoids (GCs) a di e en imes o day [41]. The modula ion
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obse ed in he ac i i y o he GCs ecep o in a ci cadian manne could be also ele an o
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o he ma e nal signals such as dopamine o mela onin [67,68,75]. These da a sugges ha
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au onomic molecula clock mechanisms ha e an ea ly ole du ing e al de elopmen , shaping
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he in luence o exogenous hy hmic signals. Simila mechanisms, ha s ill need o be
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explo ed, could be esponsible o d i ing sel -sus ained molecula oscilla ions (i.e.:
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unc ionali y) o he de eloping clock.
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The in e cellula /ci cui le el ma u a ion o he clock
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Due o i s complex s uc u e, highly di e se cell composi ion and ana omical loca ion, he
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s udy o hypo halamic de elopmen has been slowe han o o he b ain egions ( e iewed
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in [76]). The ma u a ion o he SCN as a ci cui esul om a dynamic in e play be ween ime
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cues p oduced by he mo he and in insic molecula p og ams, wi h a iable in luence along
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he pe ina al de elopmen al window. Du ing his pe iod, he SCN ci cui p og esses om a
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collec ion o undi e en ia ed indi idual cells o a highly di e en ia ed, in e connec ed and
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synch onised mul icellula ne wo k. In mice, a ound he ime o neu ogenesis (be ween
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ges a ional day (GD) 10-15), SCN cells exp ess low ampli ude clock genes oscilla ions wi h low
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in e cellula synch ony [77]. By he ime when he a e en e inal p ojec ions each he SCN
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and he eyes open (a ound pos na al day (PND) 12) [78,79], he ci cui shows high ampli ude
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clock gene oscilla ions and high in e cellula synch ony (Figu e 2). In mice and o he oden s,
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neu ons o he co e and he shell o he SCN seem o ha e di e en on ogeny iming [80].
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Cells bo n a ound GD12 a e mainly con ined o he co e, whe eas cells p oduced la e , a ound
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GD 13-14, o m he shell and dis ibu e o he pos e io and an e io a eas o he SCN [80]. To
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he bes o ou knowledge, no unc ional link o his di e en ial on ogenic iming has been
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desc ibed so a . The impo ance o pa ac ine signaling p omo ing he ne wo k le el
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p ope ies o he SCN ci cui was demons a ed in ounda ional s udies showing ha in SCN-
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lesioned oden s he sys emic hy hmici y can be es o ed by ansplan ing a g a con aining
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SCN [16], e en i he g a is w apped in a mesh blocking e e en ou g ow h [15]. In e es ingly,
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he capaci y o he g a o escue he hy hmici y s ongly depends on he age o he dono
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(g a s o hams e pups olde han PND7 lose he abili y o escue ci cadian hy hmici y) [81].
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Fu he mo e, expe imen s done wi h o gano ypic cul u es ha e shown ha he way in which
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hy hms a e coo dina ed changes along de elopmen depending on Vip and A p signaling, bu
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independen ly o he p esence o key membe s o he molecula clock machine y [82,83]. This
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was demons a ed by cul u ing neona al SCN issue slices ob ained om bo h wild- ype and
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C y1/2 double knockou mice, showing he abili y o bo h o en ain hy hmici y in an
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a hy hmic adul SCN om C y1/2 double knockou [82]. O e all, hese da a sugges ha he
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con ibu ion o pa ac ine and synap ic signaling migh change along SCN de elopmen .
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Mo eo e , GABA-e gic ci cui s, such as he SCN, migh be impac ed by he GABA exci a o y-
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inhibi o y swi ch, as he ci cui ma u es. In oden s, he swi ch elies on changes in he
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chlo ide (Cl-) low dependen on he ac i a ion o Cl--pe meable GABAa ecep o s [84]. Du ing
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de elopmen , he Na-K-2Cl co anspo e iso o m 1 (NKCC1, p omo ing Cl- accumula ion)
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down egula es, while he K-Cl co anspo e iso o m 2 (KCC2, p omo ing Cl- ex usion)
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up egula es, hus, swi ching om an exci a o y o an inhibi o y ci cui [84]. Pe u ba ions in
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he iming when his swi ch akes place ha e been p oposed as a po en ial cause o ci cui
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mis unc ion in he con ex o condi ions such as Down synd ome [85,86], epilepsy [87], au ism
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[88], Re synd ome [89–91], agile X synd ome [92,93], 22q11.2 mic odele ion synd ome
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[94], schizoph enia [95], Hun ing on’s disease [96,97] and beha io al diso de s associa ed
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wi h an ea ly ad e se en i onmen [98,99]. Howe e , o ou knowledge, his possibili y has
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no been explo ed in he con ex o SCN de elopmen . In he adul mouse SCN, he GABAe gic
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exci a ion/inhibi ion a io (E/I a io) inc eases in SCN neu ons exposed o long day
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pho ope iod compa ed o sho day pho ope iod, indica ing ha a ce ain deg ee o plas ici y
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emains e en when he ci cui is ully ma u e [100,101].
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Fu he mo e, he ac ha he unc ion o he adul ci cadian ci cui in he mouse depends on
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neu on-as ocy e in e ac ion sugges s ha he on ology migh be in luenced by (o in ol e)
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p oli e a ion and unc ional ma u a ion o as ocy es. As ocy es a e o ganized in s uc u ally
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non-o e lapping domains [102], being able o in eg a e in o ma ion a mul iple scales wi hin
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a neu onal ci cui [103] and e en o espond o signals de i ed om he en i onmen
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( e iewed in [104]). Gap junc ions-media ed communica ion ([24,105,106], e iewed in
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[107]), glu ama e elease [25] and GABA up ake [28,108] ha e been ound o be essen ial o
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he ime-keeping ole o as ocy es in he adul SCN. As ocy es can ac i ely suppo long-
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ange molecula clock synch oniza ion o seg ega ed neu onal popula ions, o which gap
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junc ions-media ed communica ion is equi ed [103]. Mo eo e , he local p oli e a ion and
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expansion o as ocy es occu ing du ing pe ina al de elopmen is ega ded as he majo
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de elopmen al o igin o as ocy es in he mammalian ce eb al co ex and migh happen also
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in he hypo halamus [109,110]. The cu en iew is ha as ocy es a e modula o s o neu onal
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communica ion and close pa ne s o neu ons o egula ing complex ci cui le el unc ions
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and beha io such as sleep ([111,112], e iewed by [113]). The e o e, i is likely ha as ocy es
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a e as he e ogeneous as neu ons in pheno ype and unc ion ([114], e iewed in [115]). Since
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as ocy es and he ci cadian sys em de elop simul aneously du ing he pe ina al pe iod in
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mice, i is possible ha as ocy es con ibu e a a ious le els o he gain o obus ness o he
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252
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254
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255
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258
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259
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260
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261
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262
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263
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264
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265
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266
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267
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268
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269
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96
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Figu e Legends
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Figu e 1: Mul iscale o ganiza ion o he ci cadian sys em. The igu e ep esen s he h ee
679
le els o o ganiza ion o he ci cadian sys em (molecula , issue/ci cui and sys emic), and
680
examples o he h ee componen s: inpu , oscilla o and ou pu ha a e essen ial o ecei ing
681
empo al cues, in eg a ing hem and synch onizing downs eam physiological p ocesses.
682
Neu ons a e ep esen ed as yellow, g een and blue ci cles and as ocy es as o ange s a s.
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Abb e ia ions: A p: asop essin, BMAL1: b ain and muscle a yl hyd oca bon ecep o nuclea
684
ansloca o -like 1, CLOCK: ci cadian locomo o ou pu cycles kapu , CRY1/2: C yp och ome
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1/2, GABA: gamma-aminobu y ic acid, GCs: glucoco icoids, Glu: glu ama e, MEL: mela onin,
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Nms: Neu omedin S, OC: op ic chiasm, Pacap: pi ui a y adenyla e-cyclase-ac i a ing
687
polypep ide, PER1/2: Pe iod 1/2, RHT: e inohypo halamic ac , SCN: sup achiasma ic nuclei,
688
T (°C): Tempe a u e, Vip: Vasoac i e in es inal pep ide, 3V: hi d en icle.
689
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Figu e 2: Timeline o he mas e clock on ogeny in mice. The igu e ep esen s he imeline
691
o he on ogeny o he hypo halamic SCN in mice du ing he pe ina al pe iod. The ci cui
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p og esses om a collec ion o undi e en ia ed indi idual cells (g ey ci cles), o a highly
693
di e en ia ed, in e connec ed and synch onised mul icellula ne wo k (neu ons as g een
694
ci cles and as ocy es as o ange s a s). In mice, a ound he ime o neu ogenesis (be ween
695
ges a ional day (GD) 10-15), SCN cells exp ess clock genes wi h low ampli ude oscilla ions and
696
low in e cellula synch ony. By he ime when he a e en e inal p ojec ions each he SCN
697
and he eyes open (a ound pos na al day (PND) 12), he ci cui exp ess clock genes wi h high
698
ampli ude oscilla ions and high in e cellula synch ony. The ma u a ion o he SCN as a ci cui
699
occu s unde he in luence o ma e nal hy hmic ho monal signals du ing bo h he p e- and
700
pos -na al pe iods (i.e.: signals ha each e al/newbo n issues h ough placen a/b eas
701
milk). Abb e ia ions: GD: Ges a ional day, Opn4: Melanopsin, PND: Pos na al day, RHT: e ino
702
hypo halamic ac .
703
704
3V
Vip
Gaba
Pho ic Glu
Pacap
RHT
Co e
Shell
A p
Nms
Gaba
Inpu Oscilla o Ou pu
OC
Ci cui Sys emic
Glu
Pacap
RHT
Pho ic
Food
T (°C)
Non-
pho ic
SCN
Ex a-SCN
Pe iphe al clocks
A p
Gaba
MEL
GCs
Molecula
Ho mones
MEL
GCs
Ho mones
24 h
BMAL1
CLOCK
PER1/2
CRY1/2
Au onomic
ne ous sys em
Clock-
con olled
genes
(CCG)
GD10-15
Neu ogenesis
GD13
Clock gene
exp ession
PND12
RHT
ma u a ion
GD15
Opn4
exp ession
GD0 GD10 GD16
BIRTH
PND10 PND30
Neu ogenesis Gliogenesis RHT
Ma e nal signals
LIGHT
GD17-PND0
Neu o-gliogenic
swi ch
GD16
Rhy hmic gene
exp ession
