title: Neurogenin3 delineates the earliest stages of spermatogenesis in the mouse testis.
abstract: In mammalian testis, a typical stem cell system ensures continuous spermatozoa production. Lines of experiments have demonstrated that stem cell activity resides in the most primitive small subset of germ cells, that is, A(s) (A(single)), A(pr) (A(paired)), and A(al) (A(aligned)) spermatogonia, also collectively called undifferentiated spermatogonia. However, their cellular or molecular nature is largely to be elucidated because a gene that is specifically expressed in these cells has not yet been identified, which makes it difficult to study them. In this study, we demonstrate that a class B basic helix-loop-helix (bHLH) transcription factor neurogenin3 (ngn3) is expressed specifically in A(s), A(pr), and A(al) spermatogonia because ngn3 is expressed in c-Kit negative spermatogonia throughout the seminiferous cycle, and transgenic labeling with GFP revealed connection of 1, 2, 4, 8, 16, or 32 ngn3-positive cells via intercellular bridges. ngn3 is first expressed at the prepubertal stage in c-Kit negative prespermatogonia. Lineage tracing, using the Cre-loxP system, demonstrates that ngn3-positive germ cells give rise to eventually all the spermatogenesis in mature testis. To our knowledge, ngn3 is the first reported gene that delineates these earliest stages of spermatogenesis. Considering its molecular nature, ngn3 could be involved in their differentiation control. Moreover, visualization with GFP and targeting expression of exogenous genes are valuable tools to investigate the mammalian spermatogenic stem cell system.
authors.affiliation: Department of Pathology and Tumor Biology, Graduate School of Medicine, Kyoto University, Kyoto, Japan. shosei@lmls.med.kyoto-u.ac.jp
authors.forename: Shosei
authors.initials: S
authors.lastname: Yoshida
authors.forename: Ayumi
authors.initials: A
authors.lastname: Takakura
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Ohbo
authors.forename: Kuniya
authors.initials: K
authors.lastname: Abe
authors.forename: Junko
authors.initials: J
authors.lastname: Wakabayashi
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Toshio
authors.initials: T
authors.lastname: Suda
authors.forename: Yo-Ichi
authors.initials: Y
authors.lastname: Nabeshima
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000502:physiology*; D013091:Spermatogenesis; D013737:Testis / Q000502:physiology*; D020798:Two-Hybrid System Techniques
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D009419:Nerve Tissue Proteins; C407737:Neurog3 protein, mouse