Ohx is a homeobox-encoding gene preferentially expressed in mature oocytes

There is abundant evidence to indicate that the homeobox genes are developmentally important. We used the NCBI dbEST databases of early mouse embryos to identify novel homeobox-containing sequence tags. Ohx (oocyte-specific homeobox gene) was one of several genes identified by in silico cloning. The full-length Ohx cDNA was cloned and its genomic organization was characterized. The Ohx gene spans 1.6 kb, encodes three exons and maps to the proximal region of mouse chromosome 7. Reverse transcriptase polymerase chain reaction analyses show that Ohx is preferentially expressed in one- and two-cell embryonic stages, as well as in the ovary. Whole mount in situ hybridization analysis demonstrates that the Ohx mRNA was exclusively localized to the oocytes of the mature ovary. Ohx is one of the few homeobox-encoding genes preferentially expressed during mammalian oogenesis.