A ZINC-FINGER DOMAIN GENE IN THE LIZARD, CALOTES-VERSICOLOR, SHOWS EXTENSIVE HOMOLOGY WITH THE MAMMALIAN ZFX AND IS EXPRESSED EMBRYONICALLY

A 590-bp long zinc finger domain DNA fragment has been isolated by pol ymerase chain reaction from the lizard, Calotes versicolor, employing the primers used for amplifying the zinc finger domain of the human Y- chromosomal gene, ZFY. Cloned in pUC18, the fragment, called CvZfa, wa s sequenced and its expression during development was studied. At the nucleotide and amino acid level CvZfa shows respectively 83% and 90% i dentity with the human ZFY, but its extent of homology is greater with the ZFX of human (86% at nucleotide and 92% at amino acid level) and the ZFY-like genes of turtle and chick. Similarly its homology with th e mouse Zfx and Zfa is much greater than that with Zfy-1 and Zfy-2. It appears that the mammalian ZFX (Zfx) evolved from reptilian ancestors with a considerable degree of conservation, but the ZFX to ZFY diverg ence within the class mammalia was more rapid. The CvZfa transcripts w ere seen in all the embryonic stages from which RNA was analysed. The whole mount in situ hybridization with the posteriorly placed mesoneph ros and the gonadal primordia of 10 to 25 day old embryos showed signa l selectively in mesonephros of the 20 and 25 day embryos. There was n o signal in the genital ridge. Thus CvZfa may not have a direct role i n gonadogenesis of C. versicolor but the possibility of its inductive role in the formation of adreno-gonadal axis through mesonephros canno t be discounted.