Transcriptome analysis reveals an unexpected role of a collagen tyrosine kinase receptor gene, Ddr2, as a regulator of ovarian function.

Mice homozygous for the smallie (slie) mutation lack a collagen receptor, discoidin domain receptor 2 (DDR2), and are dwarfed and infertile due to peripheral dysregulation of the endocrine system of unknown etiology. We used a systems biology approach to identify biological networks affected by Ddr2(slie/slie) mutation in ovaries using microarray analysis and validate findings using molecular, cellular, and functional biological assays. Transcriptome analysis indicated several altered gene categories in Ddr2(slie/slie) mutants, including gonadal development, ovulation, antiapoptosis, and steroid hormones. Subsequent biological experiments confirmed the transcriptome analysis predictions. For instance, a significant increase of TUNEL-positive follicles was found in Ddr2(slie/slie) mutants vs. wild type, which confirm the transcriptome prediction for decreased chromatin maintenance and antiapoptosis. Decreases in gene expression were confirmed by RT-PCR and/or qPCR; luteinizing hormone receptor and prostaglandin type E and F receptors in Ddr2(slie/slie) mutants, compared with wild type, confirm hormonal signaling pathways involved in ovulation. Furthermore, deficiencies in immunohistochemistry for DDR2 and luteinizing hormone receptor in the somatic cells, but not the oocytes, of Ddr2(slie/slie) mutant ovaries suggest against an intrinsic defect in germ cells. Indeed, Ddr2(slie/slie) mutants ovulated significantly fewer oocytes; their oocytes were competent to complete meiosis and fertilization in vitro. Taken together, our convergent data signify DDR2 as a novel critical player in ovarian function, which acts upon classical endocrine pathways in somatic, rather than germline, cells.