Seminiferous epithelium shows simple and uniform tubular structure. Preceding studies showed that spermatogenic stem cells are localized in a biased manner to the area associated with the vasculature and interstitium that surround the tubules. However, nature of their biased manner has not been mostly unknown at a cellular and molecular level. We have been challenging these issues by searching for genes expressed in somatic cells in proximity to blood vessels taking advantage of microdisection-microarray analyses combined with in situ hybridization screening. Our analysis has revealed that a particular somatic cell type, which is distributed in a vasculature-related pattern, express a set of genes that potentially regulate the stem cell functions such as secreted factors. In the mutant males, the number of stem cells was significantly reduced. In vitro, these cells support the cultured stem cells. Together, these cells play critical role for the stem cell niche and the biased manner of the seminiferous epithelium.