Rosa26 Locus Is Inactive in Spermatogenesis of C57BL/6 Mice

Abstract

ABSTRACT Background: The mouse Rosa26 locus demonstrates ubiquitous transcriptional activity, encoding long noncoding RNAs (LncRNAs) with no functional significance in various types of tissues and cells. It is widely employed in targeting transgene knock-in studies. However, the expression pattern of Rosa26 in the testes remains elusive. In this study, we conducted a detailed transcriptional analysis of the Rosa26 locus during mouse spermatogenesis. Methods: The transcriptional activity of the Rosa26 locus in the testes was assessed through immunohistochemistry or direct fluorescence observation in two Rosa26 locus-targeting knock-in mouse lines, Rosa26-Flag-Cas9 and Rosa26-mT/mG, both with a C57BL/6 background. The two mouse lines feature constitutively expressed Flag-tagged Cas9 and red fluorescent membrane-tethered tdTomato (mTomato) proteins. Results: In Rosa26-Flag-Cas9 mice, immunostaining of testis sections revealed robust expression of the Flag-Cas9 transgene in spermatogonia adjacent to the basement membrane of seminiferous tubules. However, its expression was absent in germ cells undergoing spermatogenesis in seminiferous tubules and in maturing spermatids in the epididymis. The transgene was also observed in intertubular Leydig cells and epididymal epithelia but was absent in Sertoli cells. Similarly, in Rosa26-mT/mG mice, fluorescence microscopy showed a complete absence of mTomato expression in the spermatogonial lineage and Sertoli cells. However, robust mTomato expression was observed in intertubular Leydig cells out of the seminiferous tubules and epididymal epithelia. Conclusion: Our findings suggest that the Rosa26 locus is inactive during spermatogenesis, indicating that functional gene studies by targeting knock-in transgenes at the Rosa26 locus in the spermatogonial lineage may not be applicable in C57BL/6 mice.