Relationship between the monosomy X phenotype and Y-linked ribosomal protein S4 (Rps4) in several species of mammals: a molecular evolutionary analysis of Rps4 homologs.

Two isoforms of the human ribosomal protein S4 gene, RPS4X and RPS4Y, are located on the X and Y chromosomes. It has been postulated that haploinsufficiency of these genes may contribute to Turner syndrome. We show here that several animal species that show the Turner-like phenotype on monosomy X have no Y-linked Rps4 homolog. There may be another gene(s) that contributes to abnormal phenotypes of monosomy X. Molecular evolutionary analysis shows that the Y-linked and RPS4X-related homologs diverged prior to the radiation of placental mammals and evolved independently. Furthermore, the functional constraints against the RPS4X-related homologs are much stronger than those against the Y-linked homologs.