Glial‐defined rhombomere boundaries in developing Xenopus hindbrain

Abstract

The vertebrate central nervous system is characterized by regional specialization, which arises during early development and contributes to patterning the emerging central nervous system (CNS). In the hindbrain, rhombomeres demarcate nonoverlapping regions of the CNS that give rise to distinct neural structures. The cellular structures that define boundaries between adjacent rhombomeres are as yet unclear. However, in certain species the boundary regions between discrete CNS regions appear to be defined by specialized glial cells. Here, we show that in developing Xenopus, DM gamma, a membrane protein of the proteolipid protein family, is expressed in a subset of radial glia. During development, DM gamma transcripts are first expressed in presumptive glial cells throughout the hindbrain, but later become confined to the ventricular zone at rhombomere centers, whereas the protein is exclusively expressed in radial glial cell processes that occupy the rhombomere boundary regions. Likewise, early in development vimentin and glial fibrillary acidic protein are extensively coexpressed in hindbrain radial glia but subsequently define distinct rhombomere domains: vimentin remains localized in radial glia at the rhombomere boundary regions, whereas expression of glial fibrillary acidic protein becomes restricted to the centers. Moreover, radial glial processes at the boundary region are distinguishable from those at the center region; the processes of the boundary region radial glia extend upward in a fan-shaped arrangement and are encircled by the processes from the center glia. These data suggest that an early event in determining rhombomere topology is the specification of both morphologically and biochemically distinct subsets of radial glia.

Glial fibrillary acidic protein and vimentin expression in the frog olfactory system during metamorphosis

“…To test the second artifactual possibility, we tested our protocol on young embryos. Our GFAP shows that, as demonstrated by Yoshida and Colman [14], GFAP decorates glia that delineate rhombomere boundaries in the developing hindbrain, attesting that our antibody is specific for Xenopus GFAP.…”

“…The first explanation for the atypical expression of GFAP would be that our antibody is not specific for GFAP in Xenopus, and/or that our immunostaining protocol is not correct. These two possibilities can be ruled out because (1) in the mouse olfactory bulb, we have reproduced the typical astrocyte staining and (2) in the spinal cord of tadpole Xenopus, our staining pattern also corresponds to the pattern described by Yoshida and Colman [14] in which GFAP decorates glia that delimit rhombomere boundaries in the developing Xenopus hindbrain. Therefore, we are confident that our GFAP staining actually reflects the expression of GFAP.…”

Rhombomere boundaries are Wnt signaling centers that regulate metameric patterning in the zebrafish hindbrain

“…This signaling system establishes zones of mutual exclusion and, thereby, prevents intermixing of cells between even and odd numbered rhombomeres. Successive rhombomeres are also separated by boundary regions showing distinctive cellular morphology and localized expression of boundaryspecific genes (Trevarrow et al, 1990;Guthrie et al, 1991;Heyman et al, 1993Heyman et al, , 1995Mahmood et al, 1995Mahmood et al, , 1996Moens et al, 1996;Yoshida and Colman, 2000). Although it has been argued that rhombomere boundaries serve as physical barriers to interrhombomeric cell migration, environmental factors and mutations that specifically ablate rhombomere boundaries do not lead to increased segmental intermixing (Nittenberg et al, 1997;White et al, 2000).…”

Ets-1 Regulates Radial Glia Formation During Vertebrate Embryogenesis

“…We focused on radial glia in the hindbrain at stage 42 ( Fig. 2B), as they were well-characterized in a previous study 51 and the expression of Ets-1 and Ets-2 overlapped with vimentin expression in the prospective hindbrain at stage 17 and 25 ( Fig. 1).…”