動物機能学講座（発生生物学講座) 

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Gametes play critical roles in inheriting genetic information from generation to generation. Above all, sperms are specially organized vehicles to convey and pass the information to eggs. Studies focused on the mode of this succession of the genome have been a major field of developmental biology and medicine (O'Donnell, 2014).

  Spermatogenesis occurs in seminiferous tubules of adult testes, in which spermatogonia, the male germline stem cells, give rise to spermatocytes, spermatids, and finally to immature spermatozoa. After moving into epididymis, the spermatozoa undergo functional maturation via exposure to an acidic microenvironment and a variety of secretory proteins in the organ (Dacheux et al., 2005).

During spermiogenesis, the final stage of the spermatogenesis, spermatids that have completed meiosis differentiate into spermatozoa with several well-defined reactions. Firstly, condensation of chromatin is caused by changing chromatin binding proteins from histones to transition proteins and finally to protamine (Bao and Bedford, 2016). Secondly, drastic morphological changes occur by developing cytoskeleton systems to create novel structures (Wu et al., 2007). Thirdly, in order to acquire the ability of movement, energy-producing mitochondria are densely packed to the midpiece (Haseeb et al., 2018), and a flagellum is constructed to the tail. Fourthly, the functions required for fertilization are equipped; acrosome for passing the zona pellucida (Hinsch and Hinsch, 1999), proteins for cell membrane fusion (Bianchi et al., 2014; Inoue et al., 2005), and protein kinases for activating eggs (Nomikos et al., 2015; Swann et al., 2004). Increasing the information about the function of the genes required for each step is essential for understanding the molecular mechanism of spermiogenesis along with finding fertility treatment.