Cell-intrinsic reprogramming capability: gain or loss of pluripotency in germ cells

Sphere-formation culture of testicular germ cells in the common marmoset, a small New World monkey

Spermatogonia are specialized cells responsible for continuous spermatogenesis and the production of offspring. Because of this biological property, in vitro culture of spermatogonia provides a powerful methodology to advance reproductive biology and engineering. However, methods for culturing primate spermatogonia are poorly established. We have designed a novel method for culturing spermatogonia in the common marmoset (Callithrix jacchus), a small primate. By using our method with a suite of growth factors, adult marmoset testis-derived germ cells could be cultured in the form of a floating sphere for several weeks. Notably, this method could be applied not only to freshly isolated cells but also to cryopreserved cell stocks. The spheres enriched spermatogonia and early spermatocytes, and could be assembled from a C-KIT(+) spermatogonial population. Techniques for culturing spermatogonia could facilitate increased understanding of primate reproduction as well as the preservation of valuable biomaterials from nonhuman primates.

The role of signaling pathways on proliferation and self-renewal of cultured bovine primitive germ cells

Purpose

Gonocytes are primitive male germ cells residing in the neonatal testes and are unipotent in nature, but also have pluripotent stem cell ability in mice under appropriate culture conditions. This study was performed to elucidate the molecular mechanisms of self-renewal and survival of cultured bovine gonocytes.

Methods

Gonocytes were isolated from neonatal bull calves and were cultured in DMEM/F12 supplemented with 15 % knock-out serum replacement (KSR) and glial cell-derived neurotrophic factor (GDNF). Cells were analyzed six days after culturing for cell-signaling molecular markers.

Results

Colony formation was observed 3-4 days after being cultured. Addition of GDNF enhanced mitogen-activated protein kinase 1/2 (MAPK1/2) phosphorylation and activated the MAPK signaling pathway. Inhibition of MAPK signaling reduced cell proliferation and abolished colony formation. However, inhibition of phosphoinositide 3-kinase-AKT (PI3K-AKT) signaling, a dominant pathway for self-renewal of mouse germ cells, did not show any effects on cultured bovine gonocytes. Expression of cell cycle-related regulators cyclin D2 and cyclin-dependent kinase 2 (CDK2) was downregulated with inhibition of MAPK signaling.

Conclusions

These results indicate activation of MAPK plays a critical role in self-renewal and survival of bovine gonocytes via cyclin D1 and CDK2.