Clustered organization and conservation of theXiphophorus maculatus D locus,which includes two distinct gene sequences

Genomic organization and chromosomal localization of a previously uncharacterizedD (Donor) locus inXiphophorus andPoecilia species was investigated using fluorescence in situ hybridization (FISH) and Southern blot analysis. Part of this region is thought to be involved in the recombination event leading to formation of theXmrk oncogene and it has recently been shown that this locus included two different genes, one with high homology to a zinc finger protein of the Krüppel type, and the other an unknown gene with high similarity to aCaenorhabditis elegans gene. FISH toXiphophorus chromosomes revealed that these two unrelated genes are closely linked and clustered at a unique chromosomal site. Southern blot hybridization patterns suggest that these genes exist in the genome as multiple copies. Furthermore, similar genomic organization profiles seem to prevail among other related fish. In particular, our FISH experiments reveal the existence of a conserved homologous chromosomal segment harboring the zinc finger protein sequence in several poeciliid fish.