Molecular and cytogenetic characterization of an Xp-chromosome deletion in cattle

In mammals male subjects have only one X with its linked genes, while female subjects have two X and two copies of linked genes. In cattle X chromosome sequence is about 148.8 Mb long with 521 RefSeq annotated genes (BosTau6 genome ssembly). In female bovine X monosomy condition seems to be unusual as till now only one case has been described (Prakash et al., 1995). In this work we report the molecular and cytogenetic characterization of a large deletion into Xp arm in a young cow that involves around 38.4 Mb of X chromosome sequence but, even though a great deal of genes is lost, all of them are involved on inactivation process. We revealed the presence of both only one normal X chromosome and a large sub-telocentric chromosome without chimeric constitution. FISH analyses, performed using specific cattle BACs mapping on both Xq and Xp arms, pointed out that the large sub-telocentric chromosome was an abnormal X chromosome with a genomic not interstitial deletion. Telomeric probes coupled with a Xq specific BAC emphasized the presence of telomeres on Xp-del with FITC-signals stronger than those produced on the normal X. Moreover, we noticed that the deleted X chromosome was always the inactivated one by analysis of X inactivation by using RBA-banding. CGH array analyses pointed out that the deletion involves the Xp arm from telomere to bp 39.449.125- 39.467.501, referred to BosTau6 cattle genome assembly while SNP analyses (SNP rs29024121) allowed us to define the maternal origin of the deletion since the wild type X derives from the father.