Chick/quail chimeras with partial cerebellar grafts: An analysis of the origin and migration of cerebellar cells

Abstract

Chick/quail chimeras with partial cerebellar grafts have been performed to obtain further information about the origin and migratory movements of cerebellar cortical neurons. The grafts were performed by exchanging between these two species a precise, small portion of the E2 cerebellar primordium, as defined in Martinez and Alvarado-Mallart (Eur. J. Neurosci. 1:549-560, 1989). All grafts were done unilaterally. The chimeric cerebella, fixed at various developmental stages, were analyzed in serial Feulgen-stained preparations to map the distribution of donor and host cells in the ependymal layer (considered to be reminiscent of the primary germinative neuroepithelium) and in the various cortical layers. In some of the oldest cases, we also used antiquail immunostaining to recognize quail cells. In the ependymal layer, it has been possible to conclude that each hemicerebellar primordium undergoes a morphogenetic rotation that changes its rostrocaudal axis to a rostromedio-caudolateral direction. However, important individual variations were observed among the chimeric embryos with respect to the ependymal area expected to be formed by donor cells. These variations cannot be explained solely on the basis of microsurgical procedure; however, they suggest the existence of important reciprocal interaction between host and grafted neuroepithelia. Therefore, it was not possible to draw a precise fate map of the E2 cerebellar primordium. Nevertheless, the dispersion of grafted cells in the cerebellar cortex, when compared to the real extent of the ependymal grafted area in each particular case, provided important data: (1) The external granular layer (EGL), the secondary germinative epithelium, seems not to originate exclusively from the "germinative trigone," as is usually considered the case. It emerges from a larger but restricted portion of the primary cerebellar matrix extending about the caudal fourth or third of the ventricular epithelium, as defined after its morphogenetic rotation. (2) The Purkinje cells (PCs) develop from all areas of the cerebellar epithelium. Although the distribution of donor PCs parallels the grafted ventricular layer mediolaterally, donor PCs extend more in the rostrocaudal dimension. The PC layer is formed mainly by donor cells in the lobules underlain by the grafted ependymal layer. However, donor PCs are also observed in cortical lobules surmounting the host ventricular layer. In these lobules, the donor PCs form clusters of various widths interrupting the host PCs. Reciprocally, clusters of host PCs are also found in the lobules formed mainly by donor PCs. The alternate small clusters of donor or host PCs are surrounded by Bergmann fibers of the other species' origin.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Cerebellar Development inmath1Null Embryos and Chimeras

“…What was surprising was our finding that some of these Math1-positive cells that originate from the ARL populate the cerebellum. The origins of all but the principal neurons of the cerebellum have been a subject of much debate (Hallonet et al, 1990;Alvarez Otero et al, 1993;Ryder and Cepko, 1994;Alder et al, 1996;Zhang and Goldman, 1996). The majority of studies addressing this issue finds that the EGL only gives rise to granule cells.…”

The isthmic organizer links anteroposterior and dorsoventral patterning in the mid/hindbrain by generating roof plate structures

“…The methods for performing small ablations, homotopic isochronic grafts (Alvarez Otero et al, 1993;Bally-Cuif and Wassef, 1994), bead implantation (Martinez et al, 1999) mesencephalic vesicle rotation including the notochord [type 1A in Marin and Puelles (Marin and Puelles, 1994)] in situ hybridization (Bally-Cuif and Wassef, 1994) and cell death assay using Nile Blue Sulfate (Louvi and Wassef, 2000) were as described with minor modifications. The DiI crystals were inserted into a small slit made in the neuroepithelium using tungsten needles.…”

“…When transplanted ectopically into competent territories, the IO induces the adjacent neuroepithelium to form supernumerary MHB structures (Martinez et al, 1991;Martinez et al, 1995), an activity mediated by FGF8 that is expressed at the MHB boundary (Crossley et al, 1996). The isthmic region is also the site of extensive cell rearrangements (Alvarez Otero et al, 1993;Louvi et al, 2003;Millet et al, 1996). Although much attention has been devoted to the understanding of the genetic interactions that position and maintain the IO (Joyner et al, 2000;Rhin and Brand, 2001;Simeone, 2000;Wurst and Bally-Cuif, 2001), less is known about the morphogenetic mechanisms that it induces.…”

The extracellular matrix provides directional cues for neuronal migration during cerebellar development

“…Cell-fate maps demonstrate that cells that will form the cerebellar anlage derive from both mesencephalic and metencephalic vesicles. On the other hand, cells that will give rise to Purkinje cells, interneurons of the molecular layer, and glial cells of the cerebellar cortex arise via radial migration from the neuroepithelium (3)(4)(5). Progenitors of the cerebellar granule cells migrate away from the roofplate via tangential movements to form the external germinal layer (5,6).…”