Normal gonadal development in mice lacking GPBOX, a homeobox protein expressed in germ cells at the onset of sexual dimorphism

Gpbox is a paired-like homeobox gene that colocalizes with two other member s of the family, PsxI and Pern, on the proximal portion of the mouse X chro mosome. Gpbox is expressed in the extraembryonic placenta and within the ge rm cells of the embryonic gonad. Beginning with the onset of sexual dimorph ism (embryonic day [E] 11.5 to 12.5), GPBOX transcripts accumulate faster i n female than in male germ cells but disappear later in embryogenesis (E16) and have not been reported in adult tissues. To investigate the function o f Gpbox, mouse cell lines lacking GPBOX were established using targeted mut agenesis in embryonic stem cells. Both homozygous Gpbox null female and hem izygous Gpbox null male mice were fertile and reproduced normally. Addition ally, the development of male and female gonads in the null background was indistinguishable from that observed in normal littermates. The lack of an obvious phenotype raises the possibility that another member of this homeob ox gene family provides the absent Gpbox function.