Expression of neuronal and glial polypeptides during histogenesis of the human cerebellar cortex including observations on the dentate nucleus

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Abstract
In order to gain a more complete understanding of the sequential pattern of gene expression during neurogenesis and gliogenesis in humans, we followed the expression of well‐characterized, developmentally regulated polypeptides in the cerebellar cortex and dentate nucleus by immunohistochemistry using monoclonal antibodies of highly defined specificity. At 8–10 weeks gestational age (GA), progenitor cells and their immediate progeny in the rhombencephalic ventricular zone expressed vimentin and nestin and, to a lesser extent, microtubule‐associated protein 5 (MAP5) and glial fibrillary acidic protein (GFAP), but not the low affinity nerve growth factor receptor (NGFR). In contrast, postmitotic, migrating immature neurons in the intermediate zone gave strong reactions for MAP2, tau, and a nonphosphorylated form of middle molecular weight neurofilament (NF) protein (NF‐M) and weak reactivity for NGFR. At 15 weeks GA, proliferating cells of the superficial part of the cerebellar external granular layer stained only for NGFR, while more deeply situated cells of the external granular layer stained positively for NGFR, MAP2, MAP5, tau, and chromogranin A, which correlates with the early outgrowth of parallel fibers. All phosphoisoforms of NF‐M as well as the low (NF‐L) and high (NF‐H) molecular weight NF proteins and alpha‐internexin were expressed in the somatodendritic domain of Purkinje cells and dentate nucleus neurons from about 20 weeks GA with a gradual compartmentalization of highly phosphorylated forms of NF‐M and NF‐H into axons by the end of gestation. Alpha‐internexin was also expressed strongly in axons of the deep white matter from 20 weeks GA to adulthood. MAP2, synaptophysin, and NGFR showed early, transient expression in the somatodendritic domain of Purkinje cells followed by the appearance of a 220 kDa nestin‐like peptide that continued to be expressed in adult Purkinje cells. Notably, developing dentate nucleus neurons expressed many of these proteins in a similar temporal sequence. Early in the developing cerebellar cortex, the expression of NF protein and synaptophysin occurred in discrete patches or columns similar to those described for other antigens (i.e., zebrins). Finally, radial glia were positive for vimentin, GFAP, and nestin from 8 weeks GA to 8 months postnatal. This study describes the distinct molecular programs of lineage commitment in cerebellar progenitor cells and in differentiating neurons and astrocytes of the human cerebellum. The acquisition of a mature molecular neuronal phenotype correlates with the establishment of structural polarity in cerebellar neurons.