AbstractDuring our search for genes required for gonadal development and function in the mouse, we identified D6Mm5e (DNA segment, Chr 6. Miriam Meisler 5, expressed), a gene with an expression pattern highly restricted to the embryonic ovary and the postnatal testis. Based on RT‐PCR, Northern blot, and in situ hybridization analyses, we show that D6Mm5e is expressed in the germ cells of the female embryo upon their initial entry into meiosis, and in male germ cells during the last stages of spermatogenesis. Two transcripts are detected in the gonads resulting from the alternative splicing of exon 8. This splicing event does not introduce a frame shift, and creates an mRNA product that uses the same stop codon as the longer transcript. Although D6Mm5e does not belong to any known protein family and does not contain any known protein signature motifs, the high level of evolutionary conservation and the cellular and temporal expression suggest that D6Mm5e may have a role in male and female gametogenesis. Here we report the gonad‐restricted mRNA expression profile of D6Mm5e in the mouse, and the evolutionary conservation of its amino acid sequence. Developmental Dynamics 235:2613–2619, 2006. © 2006 Wiley‐Liss, Inc.