The generation of a Nutm1 knock-in reporter mouse line for imaging post-meiotic spermatogenesis

Spermiogenesis, the post-meiotic stage of sperm development, is critical for normal male fertility. Many genetic defects and environmental assaults that affect spermiogenesis have been shown to be associated with male infertility. In addition, this later stage of spermatogenesis has been proposed to be an ideal target for male contraceptive development. The mouse is a widely used model for studying the mechanisms of spermatogenesis and spermiogenesis. However, due to the complexity and the asynchronous nature of spermatogenesis in adult testis, it is challenging to study molecular processes restricted to this specific developmental stage. It is also challenging to monitor the spermiogenesic activity in live mice, which is critical for screening for fertility-modulating interventions such as contraceptives. Here we reported the development of a Nutm1-T2A- luciferase 2(Luc2)-tandem Tomato(TdTomato) knock-in reporter mouse model that specifically labels post-meiotic spermatids. Homozygous reporter mice are healthy and fully fertile, demonstrating no interference with the normal functions of the Nutm1 gene by the reporter. We demonstrated the visualization of post-meiotic spermatids by fluorescent imaging of the TdTomato reporter in both live and fixed testis tissues. We also demonstrated bioluminescence imaging of Nutm1 expressing cells in live mice. The Nutm1-T2A-Luc2TdTomato reporter mouse can serve as a valuable tool for studying spermiogenesis.