Distribution of radial glia in the developing telencephalon of chicks

Abstract

Radial glia are known to have a sparse and uneven distribution in the telencephalon of adult birds. The present study utilizes antibodies against vimentin to reveal a more extensive, and more clearly radial, set of radial glia in the chicken telencephalon during the first half of embryogenesis. This initially extensive radial glial fiber system becomes distorted and reduced between 10 and 14 days of incubation. This reduction coincides with the cytoarchitectural differentiation of the telencephalon into its major adult subdivisions. Because developing neurons tend to migrate along radial glial fibers in both birds and mammals, a topological projection of these major subdivisions onto the embryonic ventricular zone along the radial glial fibers suggests hypotheses about lineage relationships that can be tested by subsequent experimental methods. This analysis suggests that the major components of the avian dorsal ventricular ridge, i.e., the ventral hyperstriatum, the neostriatum with its various subdivisions, part of the archistriatum, and probably also the piriform cortex, all derive from overlapping portions of the lateral pallial ventricular zone. Staining with antibodies against neurofilament suggests that this developmental parcellation of the lateral pallial complex is associated with the development of neuronal fiber systems.

Cell Migration and Aggregation in the Developing Telencephalon: Pulse-Labeling Chick Embryos with Bromodeoxyuridine

“…The finding that day 6 cells are distributed homogeneously throughout the Wulst, but clustered in HV, supports the hypothesis that these two structures form separate developmental compartments with distinct modes of cell migration and aggregation. The data do not provide strong support for the hypothesis that HV and Neo are separate developmental compartments because very similar isochronic cell clusters are found in HV and the dorsal neostriatum (Striedter and Beydler, 1997). However, this conclusion can be reconciled with the comparative gene expression data, which suggest that HV and Neo are separate compartments (Puelles et al, 1999(Puelles et al, , 2000, if HV and Neo become partially interdigitated during development (e.g., by the migration of some HV cells into the dorsal Neo; L. Puelles, personal communication).…”

“…It is important, therefore, to note that we use Kuhlenbeck's terminology only to the extent that it is supported by our BrdU data. A full discussion of how the BrdU data relate to the early embryonic compartmentalization of the avian telencephalon is, however, beyond the scope of the present paper (Striedter and Beydler, 1997;Puelles et al, 1999Puelles et al, , 2000. In describing the results of our long-survival experiments, we use the nomenclature most commonly used to describe newly hatched and adult chicken brains (van Tienhoven and Juhász, 1962;Youngren and Phillips, 1978;Kuenzel and Masson, 1988).…”

“…The band of labeled cells in the basal telencephalon is now more dispersed mediolaterally but remains fundamentally similar to what it looked like on day 8. The dorsal telencephalon can be tentatively divided into Neo and HV, but a definite boundary between these two regions has yet to form (Striedter and Beydler, 1997). Interestingly, labeled cells in the dorsal portion of the HV-Neo complex form clusters of 30 -100 cells (as seen in 20-m-thick sections) (Fig.…”

“…7) (our unpublished observations). Most of the migration in the Wulst probably occurs along radial glial fibers (Striedter and Beydler, 1997;Medina and Reiner, 2000), but it is possible that some older cells migrate into the Wulst along nonradial trajectories (Anderson et al, 1997).…”

“…Considerable progress has been made recently, however, by comparing embryonic rather than adult telencephalons and using immunohistochemical and gene expression data (Striedter and Beydler, 1997;Smith Fernandez et al, 1998;Puelles et al, 1999Puelles et al, , 2000Medina and Reiner, 2000). Funda- mental to these efforts has been the notion that the embryonic brain is divisible into a hierarchically organized set of developmental "compartments" (Bergquist and Källén, 1953;Garcia-Bellido et al, 1979), which can be homologized even if some of the adult structures derived from them are difficult or impossible to homologize in a simple one-for-one manner (Striedter, 1999).…”