Cell-cycle kinetics of neocortical precursors are influenced by embryonic thalamic axons.
Thalamic afferents are known to exert a control over the differentiation of cortical areas at late stages of development. Here, we show that thalamic afferents also influence early stages of corticogenesis at the level of the ventricular zone. Using an in vitro approach, we show that embryonic day 14 mouse thalamic axons release a diffusable factor that promotes the proliferation of cortical precursors over a restricted developmental window. The thalamic mitogenic effect on cortical precursors (1) shortens the total cell-cycle duration via a reduction of the G(1) phase; (2) facilitates the G(1)/S transition leading to an increase in proliferative divisions; (3) is significantly reduced by antibodies directed against bFGF; and (4) influences the proliferation of both glial and neuronal precursors and does not preclude the action of signals that induce differentiation in these two lineages. We have related these in vitro findings to the in vivo condition: the organotypic culture of cortical explants in which anatomical thalamocortical innervation is preserved shows significantly increased proliferation rates compared with cortical explants devoid of subcortical afferents. These results are in line with a number of studies at subcortical levels showing the control of neurogenesis via afferent fibers in both vertebrates and invertebrates. Specifically, they indicate the mechanisms whereby embryonic thalamic afferents contribute to the known early regionalization of the ventricular zone, which plays a major role in the specification of neocortical areas.
Dehay
C
C
Institut National de la Santé et de la Recherche Médicale U371, Cerveau et Vision, 69500 Bron, France. dehay@lyon151.inserm.fr National de la Recherche Scientifique Unité M.
Savatier
P
P
Cortay
V
V
Kennedy
H
H
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001369:Axons / Q000378:metabolism*; D001973:Bromodeoxyuridine; D002452:Cell Count; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002552:Cerebral Ventricles / Q000166:cytology / Q000196:embryology; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D016222:Fibroblast Growth Factor 2 / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006133:Growth Substances / Q000494:pharmacology; D066298:In Vitro Techniques; D051379:Mice; D019579:Neocortex / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D009475:Neurons, Afferent / Q000166:cytology / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000096:biosynthesis; D013234:Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D013788:Thalamus / Q000166:cytology / Q000196:embryology* / Q000378:metabolism
D000911:Antibodies, Monoclonal; D017077:Culture Media, Conditioned; D006133:Growth Substances; D018809:Proliferating Cell Nuclear Antigen; D016222:Fibroblast Growth Factor 2; D001973:Bromodeoxyuridine