A novel mouse line with epididymal initial segment-specific expression of Cre recombinase driven by the endogenous Lcn9 promoter

Exosc10 deficiency in the initial segment is dispensable for sperm maturation and male fertility in mice

EXOSC10 is an exosome-associated ribonuclease that degrades and processes a wide range of transcripts in the nucleus. The initial segment (IS) of the epididymis is crucial for sperm transport and maturation in mice by affecting the absorption and secretion that is required for male fertility. However, the role of EXOSC10 ribonuclease-mediated RNA metabolism within the IS in the regulation of gene expression and sperm maturation remains unknown. Herein, we established an Exosc10 conditional knockout (Exosc10 cKO) mouse model by crossing Exosc10 F/F mice with Lcn9-Cre mice which expressed recombinase in the principal cells of IS as early as post-natal day 17. Morphological and histological analyses revealed that Exosc10 cKO males had normal spermatogenesis and development of IS. Moreover, the sperm concentration, morphology, motility, and frequency of acrosome reactions in the cauda epididymides of Exosc10 cKO mice were comparable with those of control mice. Thus, Exosc10 cKO males had normal fertility. Collectively, our genetic mouse model and findings demonstrate that loss of EXOSC10 in the IS of epididymis is dispensable for sperm maturation and male fertility.

Loss of DIS3L in the initial segment is dispensable for sperm maturation in the epididymis and male fertility

DIS3L, a catalytic exoribonuclease associated with the cytoplasmic exosome complex, degrades cytoplasmic RNAs and is implicated in cancers and certain other diseases in humans. Epididymis plays a pivotal role in the transport, maturation, and storage of sperm required for male fertility. However, it remains unclear whether DIS3L-mediated cytoplasmic RNA degradation plays a role in epididymis biology and functioning. Herein, we fabricated a Dis3l conditional knockout (Dis3l cKO) mouse line in which DIS3L was ablated from the principal cells of the initial segment (IS). Morphological analyses showed that spermatogenesis and IS differentiation occurred normally in Dis3l cKO mice. Additionally, the absence of DIS3L had no dramatic influence on the transcriptome of IS. Moreover, the sperm count, morphology, motility, and acrosome reaction frequency in Dis3l cKO mice were comparable to that of the control, indicating that the Dis3l cKO males had normal fertility. Collectively, our genetic model demonstrates that DIS3L inactivation in the IS is nonessential for sperm maturation and male fertility.

Unlocking Genetic Mysteries during the Epic Sperm Journey toward Fertilization: Further Expanding Cre Mouse Lines

The spatiotemporal expression patterns of genes are crucial for maintaining normal physiological functions in animals. Conditional gene knockout using the cyclization recombination enzyme (Cre)/locus of crossover of P1 (Cre/LoxP) strategy has been extensively employed for functional assays at specific tissue or developmental stages. This approach aids in uncovering the associations between phenotypes and gene regulation while minimizing interference among distinct tissues. Various Cre-engineered mouse models have been utilized in the male reproductive system, including Dppa3-MERCre for primordial germ cells, Ddx4-Cre and Stra8-Cre for spermatogonia, Prm1-Cre and Acrv1-iCre for haploid spermatids, Cyp17a1-iCre for the Leydig cell, Sox9-Cre for the Sertoli cell, and Lcn5/8/9-Cre for differentiated segments of the epididymis. Notably, the specificity and functioning stage of Cre recombinases vary, and the efficiency of recombination driven by Cre depends on endogenous promoters with different sequences as well as the constructed Cre vectors, even when controlled by an identical promoter. Cre mouse models generated via traditional recombination or CRISPR/Cas9 also exhibit distinct knockout properties. This review focuses on Cre-engineered mouse models applied to the male reproductive system, including Cre-targeting strategies, mouse model screening, and practical challenges encountered, particularly with novel mouse strains over the past decade. It aims to provide valuable references for studies conducted on the male reproductive system.

Epithelial and mesenchymal fate decisions in Wolffian duct development

Wolffian ducts (WDs) are the paired embryonic structures that give rise to internal male reproductive tract organs. WDs are initially formed in both sexes but have sex-specific fates during sexual differentiation. Understanding WD differentiation requires insights into the process of fate decisions of epithelial and mesenchymal cells, which are tightly coordinated by endocrine, paracrine, and autocrine signals. In this review, we discuss current advances in understanding the fate-decision process of WD epithelial and mesenchymal lineages from their initial formation at the embryonic stage to postnatal differentiation. Finally, we discuss aberrant cell differentiation in WD abnormalities and pathologies and identify opportunities for future investigations.

Transcriptome profiling of the initial segment and proximal caput of mouse epididymis

Background

The proximal region of the mouse epididymis plays a pivotal role in sperm transport, sperm maturation, and male fertility. Several studies have focused on segment-dependent gene expression of the mouse epididymis through high-throughput sequencing without the precision of the microdissection.

Methods and results

Herein, we isolated the initial segment (IS) and proximal caput (P-caput) by physical microdissection using an Lcn9-cre; Rosa26tdTomato mouse model. We defined the transcriptome changes of caput epididymis by RNA sequencing (RNA-seq), which identified 1,961 genes that were abundantly expressed in the IS and 1,739 genes that were prominently expressed in the P-caput. In addition, we found that many differentially expressed genes (DEGs) were predominantly or uniquely expressed in the epididymis and region-specific genes were highly associated with transport, secretion, sperm motility, fertilization, and male fertility.

Conclusion

Thus, this study provides an RNA-seq resource to identify region-specific genes in the caput epididymis. The epididymal-selective/specific genes are potential targets for male contraception and may provide new insights into understanding segment-specific epididymal microenvironment-mediated sperm transport, maturation, and male fertility.

Epididymal DIS3 exosome ribonuclease is not necessary for mouse sperm maturation or fertility

DIS3 is an RNA exosome associated ribonuclease that degrades a wide range of transcripts that can be essential for cell survival and development. The proximal region of the mouse epididymis (initial segment and caput) plays a pivotal role in sperm transport and maturation required for male fertility. However, whether DIS3 ribonuclease mediates RNA decay in proximal epididymides remains unclear. Herein, we established a conditional knockout mouse line by crossing a floxed Dis3 allele with Lcn9-cre mice in which the recombinase is expressed in the principal cells of initial segment as early as post-natal day 17. Morphological and histological analyses, immunofluorescence, computer-aided sperm analysis and fertility were used for functional analyses. We document that DIS3 deficiency in the initial segment had no effect on male fertility. Dis3 cKO males had normal spermatogenesis and initial segment development. In cauda epididymides of Dis3 cKO mice, sperm abundance, morphology, motility, and the frequency of acrosome exocytosis were comparable to controls. Collectively, our genetic model demonstrates that loss of DIS3 in the initial segment of the epididymis is not essential for sperm maturation, motility, or male fertility.

Conditional deletion of Hspa5 leads to spermatogenesis failure and male infertility in mice

Heat shock proteins (HSPs) have important roles in different developmental stages of spermatogenesis. The heat shock 70 kDa protein 5 (HSPA5) is an important component of the unfolded protein response that promotes cell survival under endoplasmic reticulum (ER) stress conditions. In this study, we explored the function of HSPA5 in spermatogenesis, by generating a germ cell-specific deletion mutant of the Hspa5 gene (conditional knockout of the Hspa5 gene, Hspa5-cKO) using CRISPR/Cas9 technology and the Cre/Loxp system. Hspa5 knockout resulted in severe germ cell loss and vacuolar degeneration of seminiferous tubules, leading to complete arrest of spermatogenesis, testicular atrophy, and male infertility in adult mice. Furthermore, defects occurred in the spermatogenic epithelium of Hspa5-cKO mice as early as Cre recombinase expression. Germ cell ablation of Hspa5 impaired spermatogonia proliferation and differentiation from post-natal day 7 (P7) to P10, which led to a dramatic reduction of differentiated spermatogonia, compromised meiosis, and led to impairment of testis development and the disruption of the first wave of spermatogenesis. Consistent with these results, single-cell RNA sequencing (scRNA-seq) analysis showed that germ cells, especially differentiated spermatogonia, were dramatically reduced in Hspa5-cKO testes compared with controls at P10, further confirming that HSPA5 is crucial for germ cell development. These results suggest that HSPA5 is indispensable for normal spermatogenesis and male reproduction in mice.