Working map of the lampbrush chromosomes of Xenopus tropicalis: A new tool for cytogenetic analyses

Abstract

The amphibian Xenopus tropicalis, whose genome has been recently sequenced, has become an important model organism for vertebrate developmental genetics. The development of cytogenetic tools in this new model organism should contribute to an understanding of the organization of the amphibian genome and the mapping of a variety of loci of interest. In this respect, oocyte lampbrush chromosomes are particularly useful for the localization of genomic sequences expressed during oogenesis. We have constructed a working map of X. tropicalis lampbrush chromosomes, which allows the 10 bivalents of the oocyte karyotype to be readily identified by distinctive combinations of specific landmark structures composed of lateral loops, spheres, and granules. We have also established the patterns of RNA Pol III sites over the chromosomes by immunofluorescence using antibodies directed against two Pol III subunits. Specific staining patterns were found for each chromosome, which constitute a supplementary tool for their identification.

A genetic map of Xenopus tropicalis

“…Although this omission could occur for a number of reasons, our results suggest that the level of polymorphism is lower in this region than in the regions of the genome that are represented on the genetic map. Cytogenetic analyses of X. tropicalis lampbrush chromosomes (Penrad-Mobayed et al, 2009) should reveal any large-scale differences in crossover frequency for the p arm of Chr. 2.…”

Precocious detection on amphibian oocyte lampbrush chromosomes of subtle changes in the cellular localisation of the Ro52 protein induced by in vitro culture

“…a, a′, b, b′ SLLs and SLRs of bivalent XII shown in Fig. 2c, X. laevis (Murphy et al 2002) and X. tropicalis (Penrad-Mobayed et al 2009). Chromosomespecific patterns were also detected on P. waltl LBC axes with this antibody (data not shown).…”

“…Whilst the majority of the loops conform to a standard type in which the RNP matrix exhibits a fine fibrous texture, others such as the granular, globular and giant fusing loops display distinct morphologies. They are always observed at the same chromosomal loci and constitute obvious landmarks, which enabled LBC maps to be drawn up in many newt species (for a review, see Callan 1986) and in the anurans Xenopus laevis (Callan et al 1987) and Xenopus tropicalis (Penrad-Mobayed et al 2009). LBCs have also been used as a powerful system for a direct visualisation of changes in gene expression in the oocyte.…”

Examining the contents of isolated Xenopus germinal vesicles

“…An advantage of X. tropicalis over X. laevis for the study of LBCs is the smaller chromosome number (n = 10 vs n = 18) and the fact that the genome has been sequenced (http://www.xenbase.org). Working maps of the LBCs have also been published recently [35]. A.…”