Spermatogenesis is characterized by sequential transitions of multiple processes: self-renewal of spermatogonial stem cells, mitotic growth of differentiating spermatogonia, and meiosis leading to the production of sperm. Molecular dissection of these complex processes and transitions could be facilitated by cell culture approaches. We have developed techniques to recapitulate the entire spermatogenesis process, from stem cell propagation to differentiation of functional sperm, solely in culture. In addition, we have already isolated several ENU-induced zebrafish mutants that have a defect in spermatogenesis. We are working on the molecular mechanisms to regulate spermatogenesis of vertebrates both in vivo and in vitro.
Propagation and differentiation of spermatogonial stem cells (SSCs) in culture. SSCs that express green fluorescent protein grow in propagation culture (left and middle panels), while they differentiate into sperm in differentiation culture (the right panel).
Takemoto K, Imai Y, Saito K, Kawasaki T, Carlton PM, Ishiguro K, Sakai N. Sycp2 is essential for synaptonemal complex assembly, early meiotic recombination and homologous pairing in zebrafish spermatocytes. PLOS Genetics (in press)
Kawasaki T, Maeno A, Shiroishi T, Sakai N. Development and growth of organs in living whole embryo and larval grafts in zebrafish. Sci Rep. 2017 Nov 28;7(1):16508.
Higaki S, Shimada M, Kawamoto K, Todo T, Kawasaki T, Tooyama I, Fujioka Y, Sakai N, Takada T. In vitro differentiation of fertile sperm from cryopreserved spermatogonia of the endangered endemic cyprinid honmoroko (Gnathopogon caerulescens). Sci Rep. 2017 Feb 17;7:42852.
Kawasaki T, Siegfried KR, Sakai N. Differentiation of zebrafish spermatogonial stem cells to functional sperm in culture. Development. 2016 Feb 15;143(4):566-74.