Spermatogonial stem cell (SSCs) are the sources of sperm throughout adult life. Though the number of SSCs in testes is limited, they are maintained by self-renewal division. To investigate the life span of SSCs in vivo, we specifically marked SSCs of mouse testes by virus infection, and found that offspring were born from identical SSCs after >482 days. The result suggests that single SSCs can contribute to sperm production with a remarkably long life-span. We established a culture system to expand SSCs in vitro, and showed that SSCs maintain genetic and epigenetic properties after 2 year’s culture, and produced normal offspring after transplantation into testes. Using this culture system, we identified several signaling molecules involved in SSC self-renewal division. Those include GDNF and FGF2, the cytokines, both of which play important roles in SSC culture, and their downstream signaling molecules, cell cycle regulators, and glycolytic pathway. Technique to manipulate SSCs will be useful for male infertility treatment and animal transgenesis, and the knowledge of SSC self-renewal mechanism will help establishing a method to expand SSCs of a wide range of animals in vitro.

Calcium phosphates have long been used as biocompatible and osteoconductive biomaterials. Calcium phosphate-based nanocomposites with additional biofunctionality can be synthesized via coprecipitation in supersaturated calcium phosphate solutions supplemented with bioactive substances (e.g., proteins, DNA, trace elements, etc.). In this review paper, we will describe our supersaturated solution processes with and without the aid of pulsed laser irradiation for the synthesis of calcium phosphate-based thin layers and nanoparticles immobilizing selected bioactive substances. Depending on the type of bioactive substances and synthetic conditions, the resulting thin layers and nanoparticles exhibit a variety of physicochemical properties and biological functions (e.g., antibacterial activity, gene delivery capability, cell adhesion property, etc.). The calcium phosphate-based thin layers have the potential as biofunctional coating agents for biomaterials, whereas calcium phosphate-based nanoparticles have the potential as delivery carriers of therapeutic and diagnostic agents. Our synthetic processes are simple, performed under normal pressure and temperature, and require no toxic reagents, and thus, would be useful as production tools of such biofunctional calcium phosphate-based materials for diverse biomedical applications.