In germ cells, some reports noted that Notch signaling is Methyclothiazide dispensable for normal spermatogenesis. Histology of seminiferous tubules in mice with deletion of Notch1 and Pofut1, afucosyl transferase that activates all Notch receptors by transferring fucose to the Notch extracellular domain, showed normal spermatogenesis. Meanwhile, mice with Notch1 gain of function showed significantly decreased spermatogenesis and increased apoptosis of germ cells as they aged. These findings suggested that only abnormal activation of the Notch pathway could lead to the impairment of spermatogenesis. Our data are compatible with this hypothesis. In fact, NKAPL was expressed continuously in MRS 2578 postnatal testis, but its transcription was elevated by 50-fold after 3 weeks of age. Furthermore, Notch1-3 transcriptional levels in postnatal testis showed interesting changes along with age. Notch1 transcription reached a peak at 2 weeks of age and then was reduced significantly as them ice aged. Notch 2 and 3 gradually decreased with age. These results were consistent with the timing of NKAPL elevation in postnatal testis and support the hypothesis in regard to Notch signaling for spermatogenesis. Nkapl-deficient mice demonstrated elevation of differentiation factors and some characteristic changes of SSC maintenance markers. Our data on over expression of NKAPL in GS cells inversely supported this result, showing compatible changes of several factors. These findings imply that proper regulation of Notch signaling is important in sustaining the balance of spermatogonial self-renewal and differentiation. However, with which factors or signaling pathways are Notch signaling and NKAPL relevantly associated? SSC maintenance and differentiation are very complex regulated system, and each factor can activate or repress several other factors and signaling pathways. Our results revealed that overexpression of Nkapl suppressed some of the transcriptional factors associated with germ cell differentiation such as Sohlh1, Dmrt1, Lin28, Sox3, and Ngn3.Of these factors, Lin28, Sox3, and Ngn3 are expressed predominantly in undifferentiated spermatogonia, whereas Sohlh1 and Dmrt1 are expressed in differentiating spermatogonia. Some previous reports noted that Sox3, Sohlh1, and Sohlh2 stimulated Ngn3, which could be a good candidate as a central hub of SSC differentiation by being regulated by various other known differentiation factors.