PubMed · 15239185
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Elliot N Dorff. 2003. Stem cell research.. https://pubmed.ncbi.nlm.nih.gov/15239185/
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Radial glial (RG) cells have been demonstrated to be a major neural progenitor cell type, but in the human fetal brain, neither their molecular nor their spatiotemporal characteristics are well known. We used glial and neuronal-specific antibodies to determine the antigen characteristics and distribution of RG cells and other neuronal progenitors in the human brain during the first half of intrauterine development. Proliferating RG (4A4+) cells in the ventricular zone (VZ) showed clear caudorostral and ventrodorsal gradients, spreading from the spinal cord to the ventral rhombencephalon, at embryonic stages (4.5-5.5 gestational weeks [gw]). However, in the same embryo, other dividing cells expressed the neuronal marker SMI-31 and were present throughout the entire CNS, including the rostral prosencephalon. At the beginning of cortical neurogenesis (6 gw), proliferating VZ cells labeled either with neuronal markers (SMI-31, MAP2, beta-III-tubulin), double-labeled 4A4(+)/SMI-31+ cells, or cells not labeled with these antibodies, were in close proximity to each other. At midgestation (17-24 gw), RG divisions were less frequent, but were spread throughout the entire cerebral cortex, including the subventricular and intermediate zones and the subpial granular layer. Several subtypes of RG were co-labeled with vimentin and other glial markers (BLBP, GFAP, or GLAST) and quantified in vitro. In conclusion, the diversity of cortical progenitors in the human brain may, in part, explain the unique complexity of the human cerebral cortex.
The ventriculus terminalis (VT) is a dilated cavity within the conus medullaris of the spinal cord. Although the VT was discovered in the mid-nineteenth century, little is known about its characteristics during development in human fetuses. Ependymal cells lining the cavities within the CNS retain high differentiation potential, and are believed to be responsible for the postnatal neurogenesis. To evaluate the differentiation capacity of the ependymal cells lining the VT during development, we examined glial fibrillary acidic protein (GFAP) and proliferating cell nuclear antigen (PCNA) expression in the spinal cord of 18-24-week-old human fetuses. GFAP is a marker for the degree of ependymal cell differentiation in the human fetus, and PCNA is a well-known marker for cell division. Morphological characteristics of the VT were also examined. At the lower portion of the conus medullaris, the central canal abruptly expands dorsally to become the VT. Then the VT widens bilaterally while its anteroposterior diameter reduces gradually in a caudal direction. Finally, the VT becomes a narrow, transverse slit at the level of the lowermost conus medullaris. Compared with those lining the central canal, more numerous ependymal cells lining the VT showed more intensive GFAP and PCNA expression throughout all gestational ages examined. This suggests that, in the developing human spinal cord, ependymal cells lining the VT retain their differentiation potential, including a higher proliferative capacity, until a later stage of development than those lining the central canal.
Cloned bovines have a much higher abortion rate than those derived in vivo. Available evidence indicates that inappropriate epigenetic reprogramming of donor nuclei is the primary cause of cloning failure. To gain a better understanding of the DNA methylation changes associated with the high abortion rate of cloned bovines, we examined the DNA methylation status of a repeated sequence (satellite I) and the promoter regions of two single-copy genes (interleukin 3/cytokeratin) in aborted cloned fetuses, aborted fetuses derived from artificial insemination (AI), cloned adults and AI adults by bisulfite sequencing and restriction enzyme analysis. Two of four aborted cloned fetuses show very low methylation levels in the two single-copy gene promoter regions. One of the two fetuses also showed undermethylated status in the satellite I sequence. The other two aborted cloned fetuses have similar methylation levels to those of aborted AI fetuses. However, no difference in methylation was observed between cloned adults and AI adults. Our results demonstrate for the first time the undermethylated status of individual sequences in aborted cloned fetuses. These findings suggest that aberrant DNA methylation may contribute to the developmental failure of cloned bovine fetuses.