The Z-chromosome is involved in the regulation of H-W (H-Y) antigen gene expression in Xenopus.

H-W (H-Y) antigen was investigated in diploid, triploid, and tetraploid Xenopus hybrids. These hybrids differ from each other with respect to their sex chromosome constitution-they all have a single W chromosome but one to three Z chromosomes. The H-W antigen concentration is reduced with increasing numbers of Z chromosomes. In the diploid and triploid hybrids the single W chromosome is able to guarantee ovary development, but among the tetraploids both male and female animals occur. However, both sexes have identical H-W antigen titers in the somatic tissues. It can be concluded that in these tetraploid hybrids with a ZZZW sex chromosome complement, the amount of H-W antigen is too low to sustain ovary development in all cases. Our results clearly indicate that in Xenopus a Z-coded gene is involved in the regulation of H-W antigen gene expression. In man and mouse there is evidence that such a regulatory gene is located on the X chromosome. Because of the concordance of man, mouse, and Xenopus we hypothesize that not only was the H-Y (H-W) antigen gene conserved during evolution but also the genes engaged in its regulation.