|Budget Amount *help
¥25,350,000 (Direct Cost: ¥19,500,000、Indirect Cost: ¥5,850,000)
Fiscal Year 2010: ¥5,590,000 (Direct Cost: ¥4,300,000、Indirect Cost: ¥1,290,000)
Fiscal Year 2009: ¥5,460,000 (Direct Cost: ¥4,200,000、Indirect Cost: ¥1,260,000)
Fiscal Year 2008: ¥5,980,000 (Direct Cost: ¥4,600,000、Indirect Cost: ¥1,380,000)
Fiscal Year 2007: ¥8,320,000 (Direct Cost: ¥6,400,000、Indirect Cost: ¥1,920,000)
Spermatogonial stem cells (SSCs) in testes are the foundation of spermatogenesis throughout adult life. In 2003, we established a long-term in vitro culture system of mouse SSCs, and designated the cultured cells as Germline stem (GS) cells. GS cells constantly proliferate for a long-term period and expand for 10^<85>-fold (139 passages)during 2 years culture, without losing stem cell activity, normal imprinting patterns, and normal karyotype. Current research was oriented to elucidate the limitation of SSC stability, and the mechanism underlying a stability self-renewal system of SSCs, and how the breakdown of safety mechanism occurs.
First, we continued to culture GS cells beyond 2 years, and examined their life-span, and observed the effects of a long-term culture. We found that GS cells continue to proliferate for >5 years, without losing normal karyotype, but their stem cell activity and differentiation potential became gradually limited by a long-term culture.
Second, we investigated the signaling pathways regulating SSC self-renewal, and found that the signal from Glial cell line derived neurotrophic factor (GDNF), the self-renewal factor of SSCs, is transduced through Akt/PI3K pathway, and that Ras/Cyclin D2 pathway is also involved in self-renewal of SSCs. In addition, we found that p21 and p27,Cyclin-dependent kinase inhibitor (CDKI)are involved in self-renewal and differentiation of SSCs.