Expression of tamoxifen-inducible CRE recombinase in Lcn5-CreERT2 transgenic mouse caput epididymis

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.

Spectacular role of epididymis and bio-active cargo of nano-scale exosome in sperm maturation: A review

The epididymis is responsible for post-testicular sperm maturation as it provides a favorable environment for spermatozoa to gain the ability for movement and fertilization. The recent evidence has shown that, the spermatozoa are vulnerable to dynamic variations driven by various cellular exposure mechanisms mediated by epididymosomes. Exosomes provide new insight into a mechanism of intercellular communication because they provide direct evidence for the transfer of several important bio-active cargo elements (proteins, lipid, DNA, mRNA, microRNA, circular RNA, long noncoding RNA) between epididymis and spermatozoa. In broad sense, proteomic analysis of exosomes from epididymis indicates number of proteins that are involved in sperm motility, acrosomal reaction, prevent pre-mature sperm capacitation and male infertility. Pinpointing, how reproductive disorders are associated with bio-active cargo elements of nano-scale exosome in the male reproductive tract. Therefore, the current review presents evidence regarding the distinctive characteristics and functions of nano-scale exosome in the male reproductive tract in both pathological and physiological developments, and argue that these vesicles serve as an important regulator of male reproduction, fertility, and disease susceptibility.

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

Spermatozoa released from testes undergo a maturation process and acquire the capacity to fertilize ova through epididymal transit. The epididymis is divided into four regions, each with unique morphology, gene profile, luminal microenvironment and distinct function. To study the functions of relevant genes in the epididymal initial segment (IS), a novel IS-specific mouse model, Lcn9-Cre knock-in (KI) mouse line was generated via CRISPR/Cas9 technology. The TAG stop codon was replaced by a 2A-NLS-Cre cassette, resulting in the co-expression of Lcn9 and Cre recombinase. IS-specific Cre expression was first observed from postnatal day 17. Using the Rosa26^tdTomato reporter mice, the Cre-mediated DNA recombination was detected exclusively in principal cells. The epididymal IS-specific Cre activity in vivo was further confirmed using Lcn9-Cre mice crossed with a mouse strain carrying Tsc1 floxed alleles (Tsc1^flox/+). Cre expression did not affect either normal development or male fecundity. Different from any epididymis-specific Cre mice reported previously, the novel Lcn9-Cre mouse line can be used to introduce entire IS-specific conditional gene editing for gene functional study.

Preclinical models and technologies to advance nanovaccine development

The remarkable success of targeted immunotherapies is revolutionizing cancer treatment. However, tumor heterogeneity and low immunogenicity, in addition to several tumor-associated immunosuppression mechanisms are among the major factors that have precluded the success of cancer vaccines as targeted cancer immunotherapies. The exciting outcomes obtained in patients upon the injection of tumor-specific antigens and adjuvants intratumorally, reinvigorated interest in the use of nanotechnology to foster the delivery of vaccines to address cancer unmet needs. Thus, bridging nano-based vaccine platform development and predicted clinical outcomes the selection of the proper preclinical model will be fundamental. Preclinical models have revealed promising outcomes for cancer vaccines. However, only few cases were associated with clinical responses. This review addresses the major challenges related to the translation of cancer nano-based vaccines to the clinic, discussing the requirements for ex vivo and in vivo models of cancer to ensure the translation of preclinical success to patients.

The Role of the Epididymis and the Contribution of Epididymosomes to Mammalian Reproduction

It is well-established that testicular spermatozoa are immature and acquire motility and fertilization capabilities during transit throughout the epididymis. The epididymis is a duct-like organ that connects the testis to the vas deferens and is comprised of four anatomical regions: the initial segment, caput, corpus, and cauda. Sperm maturation occurs during epididymal transit by the interaction of sperm cells with the unique luminal environment of each epididymal region. In this review we discuss the epididymis as an essential reproductive organ responsible for sperm concentration, maturation (including sperm motility acquisition and fertilizing ability), protection and storage. Importantly, we also discuss specific characteristics and roles of epididymal-derived exosomes (epididymosomes) in establishing sperm competency within the intricate process of reproduction. This review suggests that an increasing body of evidence is working to develop a complete picture of the role of the epididymis in male reproduction, offspring health, and disease susceptibility.

A Simple Combined Use of CRISPR-Cas9 and Cre-LoxP Technologies for Generating Conditional Gene Knockouts in Mammalian Cells

Gene knockout technologies have contributed fundamentally to our understanding of the cellular functions of various genes. Two prevalent systems used for the efficient elimination of the expression of specific genes are the Cre-LoxP system and the CRISPR-Cas9 system. Here, we present a simple method that combines the use of CRISPR-Cas9 and Cre-LoxP for the conditional deletion of essential genes in mammalian cells. First, an inducible Cre recombinase is stably expressed in the cells. Next, CRISPR-Cas9 is used to knock out an essential gene, whose function is complemented by stable expression of a FLAG-tagged version of the same protein encoded from a floxed transcription unit containing silent mutations, making it refractory to the CRISPR-Cas9 guide. This FLAG-tagged protein can be deleted by activating the expressed Cre protein, enabling evaluation of the cellular consequences of its deletion. We have further used this system to evaluate the ability of phylogenic homologues and of potential mutants to cover functionally for the deleted gene.