Embryonic and early fetal development of the human neocortex.
Early corticogenesis was studied in human embryos and early fetuses from Carnegie stages 16 to 22 (5-8 gestational weeks) by using immunohistochemistry for Reelin (Reln), calretinin (CR), and glutamic acid decarboxylase (GAD). A first population of Reln-positive cells appears in the neocortical anlage at stage 16 and increases in number at stages 17-18. At stages 19-20, a monolayer of horizontal CR- and GAD-positive, Reln-negative neurons forms in the preplate, whereas Reln-positive cells shift into a subpial position. Another cell class, the pioneer projection neuron, is CR-positive but GAD- and Reln-negative; pioneer cells contribute early corticofugal axons. Pioneer cells first appear below the monolayer at stage 20 and form a pioneer plate at stage 21. The cortical plate (CP) proper emerges at stage 21 and inserts itself within the pioneer plate, which is thus split into a minor superficial component and a larger deep component that presumably corresponds to the subplate. Initial CP neurons are radially organized and mostly CR-negative. Reln-positive cells remain consistently segregated from the pioneer cells and are thus not directly involved in preplate partition. Our data indicate that the neuronal composition of the human neocortical preplate is more complex than generally described and that various neurons participate in a sequence of events that precede the emergence of the CP.
Meyer
G
G
Department of Anatomy, Faculty of Medicine, University La Laguna, 38071 La Laguna/Tenerife, Spain. gmeyer@ull.es
Schaaps
J P
JP
Moreau
L
L
Goffinet
A M
AM
D064032:Calbindin 2; D015816:Cell Adhesion Molecules, Neuronal / Q000032:analysis; D002465:Cell Movement; D016326:Extracellular Matrix Proteins / Q000032:analysis; D005333:Fetus / Q000737:chemistry / Q000166:cytology / Q000201:enzymology; D005865:Gestational Age; D005968:Glutamate Decarboxylase / Q000032:analysis; D006801:Humans; D019579:Neocortex / Q000166:cytology / Q000196:embryology*; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000737:chemistry / Q000166:cytology* / Q000201:enzymology; D000091042:Reelin Protein; D064030:S100 Calcium Binding Protein G / Q000032:analysis; D012697:Serine Endopeptidases
C576764:CALB2 protein, human; D064032:Calbindin 2; D015816:Cell Adhesion Molecules, Neuronal; D016326:Extracellular Matrix Proteins; D009419:Nerve Tissue Proteins; D000091042:Reelin Protein; D064030:S100 Calcium Binding Protein G; C000717127:RELN protein, human; D012697:Serine Endopeptidases; D005968:Glutamate Decarboxylase