Evidence for specific RNA/protein interactions in the differential segment of the W sex chromosome in the amphibian Pleurodeles waltl.

Pleurodeles exhibits a ZZ/ZW system of GSD (genotype sex determination). However, the Z and W sex chromosomes appear to be morphologically identical. A short RNA sequence is described that was specifically bound to lampbrush loops in the differential segment of the sexual bivalent IV. The distribution of these labeled loops in experimentally produced ZZ and WW females enabled us to demonstrate that such labeled loops were perfectly correlated with the W chromosome. Therefore, this RNA sequence constitutes an excellent marker for the W differential segment. Furthermore, analysis of the labeled loops under various experimental conditions suggested that their labeling is caused by specific interactions between this RNA sequence and lampbrush loop-associated proteins (RNA/protein interactions). North-western assays revealed that nuclear polypeptide(s) of 65 kDa could be responsible for such binding.