Nobox is a homeobox-encoding gene preferentially expressed in primordial and growing oocytes

To identify novel genes involved in early mammalian folliculogenesis, we used the Unigene collection of mouse cDNA libraries to identify unique expressed sequence tags in a newborn mouse ovary cDNA library. Nobox (newborn ovary homeobox-encoding gene) was one of several genes identified by in silico (electronic database) subtraction. We cloned the mouse Nobox cDNA and characterized its genomic organization. The gene spans 14kb and is encoded by eight exons. The Nobox gene maps to proximal chromosome 6 in the mouse, and we identified a portion of the human gene encoding a NOBOX homolog which resides at a syntenic position on chromosome 7q35. Reverse transcriptase polymerase chain reaction and Northern blot analyses show that Nobox is preferentially expressed in the ovary at high levels. In situ hybridization analysis demonstrates that Nobox mRNA is present in primordial and growing oocytes. Nobox is one of the first homeobox-encoding genes preferentially expressed during mammalian folliculogenesis.