Expression of morphogenic genes in mature ovarian and testicular tissues: potential stem-cell niche markers and patterning factors.

Morphogens are developmental regulators that modulate different tissue patterning, proliferation, differentiation, or remodeling processes in embryonic and adult tissues. Morphogens may also evoke specific regulatory programs in stem cells. Some of the morphogens involved in these processes have been characterized, while others remain unidentified. A microarray containing 3,557 salmonid cDNAs was used to compare the transcriptomes of rainbow trout precocious ovary at three different stages during second year (June, August, and October) with a reference (June normal ovary) transcriptome. During this study, we detected morphogen transcript hybridizations to salmonid elements and the study was enlarged to investigate these activities in various developmental stages of both ovary and testis. Genes from diverse development regulator families such as Anterior gradient-2, BMP, Epimorphin, Flightless, Frizzled, Notch, Tiarin, Twisted gastrulation, and Wnt were demonstrated to be expressed in the adult trout gonads. In mice or rats, expression of mammalian bmp-4, epimorphin, flightless, twisted gastrulation, and GW112 transcripts were localized to cell types isolated from the developed ovary and testis. Comparisons of salmonid and mammalian morphogens at the amino acid residue level show high similarities, suggesting functional conservation. This report provides evidence for local regulation by various morphogens and their potential to control distinct programs of gene expression in the gametes and their accessory cells during gametogenesis.