We report a cross-species expression profiling analysis of the human, mouse, and rat male meiotic transcriptional program, using enriched germ cell populations, whole gonads, and high-density oligonucleotide microarrays (GeneChips). Among 35% of the protein-coding genes present in rodent and human genomes that were found to be differentially expressed between germ cells and somatic controls, a key group of 357 conserved core loci was identified that displays highly similar meiotic and postmeiotic patterns of transcriptional induction across all three species. Genes known to be important for sexual reproduction are significantly enriched among differentially expressed core loci and a smaller group of conserved genes not detected in 17 nontesticular somatic tissues, correlating transcriptional activation and essential function in the male germ line. Some genes implicated in the etiology of cancer are found to be strongly transcribed in testis, suggesting that these genes may play unexpected roles in sexual reproduction. Expression profiling data further identified numerous conserved genes of biological and clinical interest previously unassociated with the mammalian male germ line.bioinformatics ͉ spermatogenesis ͉ transcriptome

SUMMARYGerm cells, the embryonic precursors of sperm or oocytes, respond to molecular cues that regulate their sex-specific development in the fetal gonads. In males in particular, the balance between continued proliferation and cell fate commitment is crucial: defects in proliferation result in insufficient spermatogonial stem cells for fertility, but escape from commitment and prolonged pluripotency can cause testicular germ cell tumors. However, the factors that regulate this balance remain unidentified. Here, we show that signaling by the TGF morphogen Nodal and its co-receptor Cripto is active during a crucial window of male germ cell development. The Nodal pathway is triggered when somatic signals, including FGF9, induce testicular germ cells to upregulate Cripto. Germ cells of mutant mice with compromised Nodal signaling showed premature differentiation, reduced pluripotency marker expression and a reduced ability to form embryonic germ (EG) cell colonies in vitro. Conversely, human testicular tumors showed upregulation of NODAL and CRIPTO that was proportional to invasiveness and to the number of malignant cells. Thus, Nodal signaling provides a molecular control mechanism that regulates male germ cell potency in normal development and testicular cancer.

This work was supported by the Proteomics Core Facility at Biogenouest and was funded by Conseil Régional de Bretagne, IBiSA and Agence de la Biomédecine grants. The authors declare that there exists a competing financial interest in this work that is related to a patent application on the use of identified germ cell-specific proteins in an antibody-based assay (Fertichip™) to predict the successful testicular biopsy outcomes in human non-obstructive azoospermia.