title: Cyclin D2 is critical for intermediate progenitor cell proliferation in the embryonic cortex.
abstract: Expression of cyclins D1 (cD1) and D2 (cD2) in ventricular zone and subventricular zone (SVZ), respectively, suggests that a switch to cD2 could be a requisite step in the generation of cortical intermediate progenitor cells (IPCs). However, direct evidence is lacking. Here, cD1 or cD2 was seen to colabel subsets of Pax6-expressing radial glial cells (RGCs), whereas only cD2 colabeled with Tbr2. Loss of IPCs in cD2(-/-) embryonic cortex and analysis of expression patterns in mutant embryos lacking cD2 or Tbr2 indicate that cD2 is used as progenitors transition from RGCs to IPCs and is important for the expansion of the IPC pool. This was further supported by the laminar thinning, microcephaly, and selective reduction in the cortical SVZ population in the cD2(-/-)cortex. Cell cycle dynamics between embryonic day 14-16 in knock-out lines showed preserved parameters in cD1 mutants that induced cD2 expression, but absence of cD2 was not compensated by cD1. Loss of cD2 was associated with reduced proliferation and enhanced cell cycle exit in embryonic cortical progenitors, indicating a crucial role of cD2 for the support of cortical IPC divisions. In addition, knock-out of cD2, but not cD1, affected both G(1)-phase and also S-phase duration, implicating the importance of these phases for division cycles that expand the progenitor pool. That cD2 was the predominant D-cyclin expressed in the human SVZ at 19-20 weeks gestation indicated the evolutionary importance of cD2 in larger mammals for whom expansive intermediate progenitor divisions are thought to enable generation of larger, convoluted, cerebral cortices.
authors.affiliation: Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA.
authors.forename: Sara B
authors.initials: SB
authors.lastname: Glickstein
authors.forename: Julie A
authors.initials: JA
authors.lastname: Monaghan
authors.forename: Hajira B
authors.initials: HB
authors.lastname: Koeller
authors.forename: Tiffanie K
authors.initials: TK
authors.lastname: Jones
authors.forename: M Elizabeth
authors.initials: ME
authors.lastname: Ross
mesh_terms: D000818:Animals; D001921:Brain / Q000196:embryology / Q000502:physiology; D002453:Cell Cycle / Q000502:physiology; D049109:Cell Proliferation; D002540:Cerebral Cortex / Q000196:embryology* / Q000502:physiology*; D019938:Cyclin D1 / Q000378:metabolism; D056742:Cyclin D2; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009457:Neuroglia / Q000502:physiology; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D013234:Stem Cells / Q000502:physiology*; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
chemical_list: C530104:CCND1 protein, human; C080336:CCND2 protein, human; C530105:Ccnd1 protein, mouse; C486196:Ccnd2 protein, mouse; D056742:Cyclin D2; D016213:Cyclins; C491198:Eomes protein, mouse; D005136:Eye Proteins; D018398:Homeodomain Proteins; D000071841:PAX6 Transcription Factor; C000605730:PAX6 protein, human; D051761:Paired Box Transcription Factors; C000605732:Pax6 protein, mouse; D012097:Repressor Proteins; D020825:T-Box Domain Proteins; D019938:Cyclin D1