Deficiency for Lcn8 causes epididymal sperm maturation defects in mice

Single-cell RNA sequencing unveils dynamic transcriptional profiles during the process of donkey spermatogenesis and maturation

INTRODUCTION

With the increasing demand for donkey production, there has been a growing focus on the breeding of donkeys. However, our current understanding of the mechanisms underlying spermatogenesis and maturation in donkeys during reproduction remains limited.

OBJECTIVES

This study is to provide a comprehensive single-cell landscape analysis of spermatogenesis and maturation in donkeys.

METHODS

In this study, we employed single-cell RNA sequencing to investigate cell composition, gene expression patterns, and regulatory roles during spermatogenesis and maturation in donkeys.

RESULTS

The expression patterns of CDK1, CETN3, and UBE2J1 were found to be indicative of specific germ cells during donkey spermatogenesis. Additionally, the DEFB121, ELSPBP1, and NPC2 genes were specifically identified in the principal cells of the donkey epididymis.

CONCLUSIONS

We performed single-cell RNA sequencing to analyze the cellular composition and spatial distribution of donkey testis and epididymis, thereby generating comprehensive transcriptional atlases at the single-cell resolution.

Comprehensive time-course gene expression evaluation of high-risk beef cattle to establish immunological characteristics associated with undifferentiated bovine respiratory disease

Bovine respiratory disease (BRD) remains the leading infectious disease in beef cattle production systems. Host gene expression upon facility arrival may indicate risk of BRD development and severity. However, a time-course approach would better define how BRD development influences immunological and inflammatory responses after disease occurrences. Here, we evaluated whole blood transcriptomes of high-risk beef cattle at three time points to elucidate BRD-associated host response. Sequenced jugular whole blood mRNA from 36 cattle (2015: n = 9; 2017: n = 27) across three time points (n = 100 samples; days [D]0, D28, and D63) were processed through ARS-UCD1.2 reference-guided assembly (HISAT2/Stringtie2). Samples were categorized into BRD-severity cohorts (Healthy, n = 14; Treated 1, n = 11; Treated 2+, n = 11) via frequency of antimicrobial clinical treatment. Assessment of gene expression patterns over time within each BRD cohort was modeled through an autoregressive hidden Markov model (EBSeq-HMM; posterior probability ≥ 0.5, FDR < 0.01). Mixed-effects negative binomial models (glmmSeq; FDR < 0.05) and edgeR (FDR < 0.10) identified differentially expressed genes between and across cohorts overtime. A total of 2,580, 2,216, and 2,381 genes were dynamically expressed across time in Healthy, Treated 1, and Treated 2+ cattle, respectively. Genes involved in the production of specialized resolving mediators (SPMs) decreased at D28 and then increased by D63 across all three cohorts. Accordingly, SPM production and alternative complement were differentially expressed between Healthy and Treated 2+ at D0, but not statistically different between the three groups by D63. Magnitude, but not directionality, of gene expression related to SPM production, alternative complement, and innate immune response signified Healthy and Treated 2+ cattle. Differences in gene expression at D63 across the three groups were related to oxygen binding and carrier activity, natural killer cell-mediated cytotoxicity, cathelicidin production, and neutrophil degranulation, possibly indicating prolonged airway pathology and inflammation weeks after clinical treatment for BRD. These findings indicate genomic mechanisms indicative of BRD development and severity over time.

The Sperm-Associated Antigen 11A (Spag11a) Knockout Mice Display Sub-Fertility and Perturbations in the Sperm Proteome

Spermatogenesis and sperm maturation that occur in the testis and epididymis respectively are crucial for fertility. Factors secreted by the testicular and epididymal epithelial cells govern the processes of gametogenesis and maturation. Proteins encoded by the sperm-associated antigen 11a (Spag11a) gene are implicated as having a possible role in sperm maturation. However, studies that demonstrate their definite role in fertility and sperm function using knockout models have not yet reported. In this study, Spag11a knockout mice were generated, genotyped and the reproductive parameters (fecundity, sperm count, capacitation, and acrosome reaction) and sperm proteome were determined. Litter size and sperm count were decreased in the Spag11a knockout mice when compared to the wild-type controls. Spermatozoa from the knockout mice were able to undergo capacitation. However, acrosome reaction did not occur in sperm obtained from knockout mice. Structural abnormalities in the head and tail structures were evident in the spermatozoa of knockout mice. Perturbations in the expression of sperm proteins that are involved in gametogenesis were evident. The subfertility observed in Spag11a knockout mice could be a manifestation of lower sperm count, impaired acrosome reactions, and disturbances in the sperm proteome. The results of this study lend further support to the role of Spag11a gene in male gamete function.

The single-cell atlas of the epididymis in mice reveals the changes in epididymis function before and after sexual maturity

Introduction: The epididymis is important for sperm transport, maturation, and storage. Methods: The head and tail of the epididymis of 5-week-old and 10-week-old C57 BL/6J male mice were used for single-cell sequencing. Results: 10 cell types including main, basal, and narrow/clear cells are identified. Next, we performed cell subgroup analysis, functional enrichment analysis, and differentiation potential prediction on principal cells, clear cells, and basal cells. Our study indicates that the principal cells are significantly involved in sperm maturation, as well as in antiviral and anti-tumor immune responses. Clear cells are likely to play a crucial role in safeguarding sperm and maintaining epididymal pH levels. Basal cells are implicated in the regulation of inflammatory and stress responses. The composition and functions of the various cell types within the epididymis undergo significant changes before and after sexual maturity. Furthermore, pseudo-temporal analysis elucidates the protective and supportive roles of epididymal cells in sperm maturation during sexual maturation. Discussion: This study offers a theoretical framework and forecasts for the investigation of epididymal sperm maturation and epididymal immunity.

Region-specific gene expression profile in the epididymis of high- and low-fertile dromedary camels

The scenario of the fertile spermatozoa with high fertilizing capability is basically dependent on gene expression-based epididymal function. The current investigation aimed to declare the varied expression of different candidate genes (PLA2G4D, LCN15, CLUAP1, SPP1, AQP12B, DEFB110 and ESR1) relevant to spermatozoa features between the different epididymal segments in the mature dromedary camels (n = 30). Scrotal contents were collected post-slaughtering, during the breeding season and the epididymis was separated from the testicles and divided into three segments (caput, corpus and cauda) based on its morphology and anatomical characteristics. Epididymal spermatozoa were harvested from each epididymal portion and evaluated for motility, count, viability and morphology. Samples were grouped depending on their epididymal sperm cells features into high-fertile (n = 15) and low-fertile (n = 15) groups. The gene expression of the candidate genes was defined in the isolated RNA from each epididymal portion tissue. The segmental sperm motion and count were significantly (p < .05 and p < .01) higher in the three epididymal parts of high-fertile camels than the lower ones. There were some candidate genes markedly up-regulated in its expression in epididymal head of high-fertile camels (PLA2G4D and LCN15) and low fertile (CLUAP1), while others in the body region of the high-fertile group (SPP1, AQP12B and DEFB110). Nevertheless, ER1 did not differ in the expression among the epididymal segments. In conclusion, the variant expression patterns of these epididymal genes in relation to the regional spermatozoa features might suggest important roles of these genes in sperm maturation process in the epididymis and focusing more interest on their potential utility as markers for male camel fertility prediction.

CRISPR/Cas9-mediated disruption of lipocalins, Ly6g5b, and Ly6g5c causes male subfertility in mice

BACKGROUND

Spermatozoa become mature and competent for fertilization during transit from the caput epididymis to the cauda epididymis. However, detailed molecular mechanisms of epididymal sperm maturation are still unclear. Here, we focused on multiple epididymis-enriched genes: lipocalin family genes (Lcn5, Lcn6, Lcn8, Lcn9, and Lcn10) and Ly6 family genes (Ly6g5b and Ly6g5c). These genes are evolutionarily conserved in mammals and form clusters on chromosomes 2 and 17 in the mouse, respectively.

OBJECTIVE

To clarify whether these genes are required for epididymal sperm maturation and acquisition of fertilizing ability, we generated knockout (KO) mice using the CRISPR/Cas9 system and analyzed their phenotype.

MATERIALS AND METHODS

We generated four lines of KO mice: Lcn9 single KO, the lipocalin family quadruple KO (Lcn5, Lcn6, Lcn8, and Lcn10), quintuple KO (Lcn5, Lcn6, Lcn8, Lcn10, and Lcn9), and double KO of Ly6 family genes (Ly6g5b and Ly6g5c).

RESULTS

Although the Lcn9 single KO did not affect male fertility, the quadruple KO and quintuple KO male mice were subfertile and mostly infertile, respectively, with a reduced amount of ADAM3, an essential protein for sperm binding to the zona pellucida. Further analysis revealed that the quintuple KO spermatozoa lack the CMTM2A/B that are required for ADAM3 maturation. Intriguingly, Ly6g5b and Ly6g5c double KO male mice also showed subfertility with reduced sperm ADAM3.

CONCLUSION

These results suggest epididymal secretory proteins are involved in ADAM3 maturation and acquisition of sperm fertilizing ability.

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.

Mechanisms That Protect Mammalian Sperm from the Spontaneous Acrosome Reaction

To acquire the capacity to fertilize the oocyte, mammalian spermatozoa must undergo a series of biochemical reactions in the female reproductive tract, which are collectively called capacitation. The capacitated spermatozoa subsequently interact with the oocyte zona-pellucida and undergo the acrosome reaction, which enables the penetration of the oocyte and subsequent fertilization. However, the spontaneous acrosome reaction (sAR) can occur prematurely in the sperm before reaching the oocyte cumulus oophorus, thereby jeopardizing fertilization. One of the main processes in capacitation involves actin polymerization, and the resulting F-actin is subsequently dispersed prior to the acrosome reaction. Several biochemical reactions that occur during sperm capacitation, including actin polymerization, protect sperm from sAR. In the present review, we describe the protective mechanisms that regulate sperm capacitation and prevent sAR.

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.

Single-cell RNA sequencing reveals the local cell landscape in mouse epididymal initial segment during aging

BACKGROUND

Morphological and functional alterations in aging reproductive organs result in decreased male fertility. The epididymis functions as the transition region for post-testicular sperm maturation. And we have previously demonstrated that the epididymal initial segment (IS), a region of the reproductive tract essential for sperm maturation and capacitation, undergoes considerable histological changes and chronic immune activation in mice during aging. However, the local aging-associated cellular and molecular changes in the aged epididymal IS are poorly understood.

RESULTS

We conducted single-cell RNA sequencing analysis on the epididymal IS of young (3-month-old) and old (21-month-old) mice. In total, 10,027 cells from the epididymal IS tissues of young and old mice were obtained and annotated. The cell composition, including the expansion of a principal cell subtype and Ms4a4b^HiMs4a6b^Hi T cells, changed with age. Aged principal cells displayed multiple functional gene expression changes associated with acrosome reaction and sperm maturation, suggesting an asynchronous process of sperm activation and maturation during epididymal transit. Meanwhile, aging-related altered pathways in immune cells, especially the "cell chemotaxis" in Cx3cr1^Hi epididymal dendritic cells (eDCs), were identified. The monocyte-specific expression of chemokine Ccl8 increased with age in eDCs. And the aged epididymal IS showed increased inflammatory cell infiltration and cytokine secretion. Furthermore, cell-cell communication analysis indicated that age increased inflammatory signaling in the epididymal IS.

CONCLUSION

Contrary to the general pattern of lower immune responses in the male proximal genital tract, we revealed an inflammaging status in mouse epididymal initial segment. These findings will allow future studies to enable the delay of male reproductive aging via immune regulation.

Identification, characterization and expression analysis of rLcn13, an epididymal lipocalin in rats

As the essential tissue for sperm maturation and storage, the epididymis secretes a number of tissue-specific proteins to exert its functions. Among these proteins, epididymal lipocalins have been intensively studied because of their epididymis-specific expression pattern and clustered genomic organization. In this study, rLcn13, a member of the rat epididymal lipocalin family, is identified and elaborately characterized. The cDNA sequence of rLcn13 consists of 719 nucleotides and encodes a 176 amino-acid protein with a predicted N-terminal signal peptide of 19 amino acids. rLcn13 shares a similar genomic structure and predicted 3D protein structure with other lipocalin family members. A recombinant rLCN13 mature peptide of 157 amino acids is expressed and purified, which is used to raise a polyclonal antibody against rLCN13 with high specificity and sensitivity. Northern blot, western blot, and immunohistochemistry assays reveal that rLcn13 is an epididymis-specific gene which is expressed predominantly in the initial segment and proximal caput epididymis and influenced by androgen. The rLCN13 protein is modified by N-glycosylation and secreted into the epididymal lumen, and then binds to the acrosome region of the sperm. Our data demonstrate that rLcn13 exhibits a specific temporospatial expression pattern and androgen dependence, indicating its potential roles in sperm maturation.

Identification and characterization of lipocalin-type prostaglandin D2 synthase homologs in the urine of male rockfish

Black rockfish (Sebastes schlegelii) and its relatives are viviparous marine fish. Males produce urinary proteins during the copulation season; however, the identity of these proteins was unknown. In this study, we focused on high-molecular-weight urinary proteins (HMWups) in male black rockfish. The HMWups were identified by liquid chromatography and tandem mass spectrometry (LC-MS/MS) of urine. In silico analyses of RNA-seq data predicted the tissue distribution of candidate HMWup transcripts and their gene structures. Candidate cDNAs were cloned and a recombinant protein of a major candidate was prepared. Western blotting of urine using an antiserum against the recombinant protein was performed to reconfirm the LC-MS/MS results. Quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry were employed to validate the prediction by RNA-seq and identify the cells producing HMWups, respectively. LC-MS/MS, in conjunction with Western blotting and cDNA cloning, identified the HMWups as lipocalin-type prostaglandin D₂ synthase (l-PGDS) homologs. RNA-seq analyses and qRT-PCR revealed that the l-PGDS homolog transcripts were dominantly expressed in the testis and male kidney; Sertoli cells and epithelial cells in the renal tubules were immunoreactive. These results indicated that major protein components in the urine of male black rockfish are l-PGDS homologs, potentially produced by the renal tubules in the kidney. Male rockfish (genus Sebastes) are thought to release unknown pheromone substances during mating behavior. The knowledge and tools obtained in this study empower research into the role(s) of HMWups in pheromone systems underlying rockfish reproduction. No protein-type teleost pheromone has heretofore been discovered.

Proteomic analysis of the mouse sperm acrosome - towards an understanding of an organelle with diverse functionality

The acrosome located within the mammalian sperm head is essential for successful fertilization, as it enables the sperm to penetrate the extracellular layers of the oocyte and fuse with oolemma. However, the mammalian acrosomal vesicle is no longer considered to contain only hydrolytic enzymes. Using label-free nano-scale liquid chromatography tandem mass spectrometry (nLC-MS/MS) proteomics, we identified a total of 885 proteins in the acrosome isolated from spermatozoa obtained from cauda epididymis of free-living house mice Mus musculus musculus contains a total of 885 proteins. Among these, 334 proteins were significantly enriched in the acrosome thus representing 27.3% of the whole proteome of the intact sperm. Importantly, we have detected a total of nine calycins while eight of them belong to the lipocalin protein family. In mice, lipocalins are involved in multi-level chemical communication between individuals including pheromone transport and odor perception. Using an indirect immunofluorescence assay, we demonstrated that lipocalin 5 (LCN5) is expressed in the mouse germ cells, and after completing spermatogenesis, it remains localized in the sperm acrosome until the last step of the extratesticular maturation, the acrosome reaction. The presence of lipocalins in the acrosome and acrosome-reacted sperm suggests their original role as chelators of organic and potentially toxic compounds resulting from ongoing spermiogenesis. Along with this evidence, detected mitochondrial (e.g., a subunit of the cytochrome c oxidase MTCO1) and proteasomal proteins (subunits of both 20 S core proteasome [PSMA2, PSMBs] and 19 S regulatory particle [PSMDs]) in acrosomes provide further evidence that acrosomes could also function as `waste baskets` after testicular sperm maturation.

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.

Application of CRISPR/Cas Technology in Spermatogenesis Research and Male Infertility Treatment

As the basis of animal reproductive activity, normal spermatogenesis directly determines the efficiency of livestock production. An in-depth understanding of spermatogenesis will greatly facilitate animal breeding efforts and male infertility treatment. With the continuous development and application of gene editing technologies, they have become valuable tools to study the mechanism of spermatogenesis. Gene editing technologies have provided us with a better understanding of the functions and potential mechanisms of action of factors that regulate spermatogenesis. This review summarizes the applications of gene editing technologies, especially CRISPR/Cas9, in deepening our understanding of the function of spermatogenesis-related genes and disease treatment. The problems of gene editing technologies in the field of spermatogenesis research are also discussed.

Genome-Wide Association Studies, Runs of Homozygosity Analysis, and Copy Number Variation Detection to Identify Reproduction-Related Genes in Bama Xiang Pigs

Litter size and teat number are economically important traits in the porcine industry. However, the genetic mechanisms influencing these traits remain unknown. In this study, we analyzed the genetic basis of litter size and teat number in Bama Xiang pigs and evaluated the genomic inbreeding coefficients of this breed. We conducted a genome-wide association study to identify runs of homozygosity (ROH), and copy number variation (CNV) using the novel Illumina PorcineSNP50 BeadChip array in Bama Xiang pigs and annotated the related genes in significant single nucleotide polymorphisms and common copy number variation region (CCNVR). We calculated the ROH-based genomic inbreeding coefficients (FROH) and the Spearman coefficient between FROH and reproduction traits. We completed a mixed linear model association analysis to identify the effect of high-frequency copy number variation (HCNVR; over 5%) on Bama Xiang pig reproductive traits using TASSEL software. Across eight chromosomes, we identified 29 significant single nucleotide polymorphisms, and 12 genes were considered important candidates for litter-size traits based on their vital roles in sperm structure, spermatogenesis, sperm function, ovarian or follicular function, and male/female infertility. We identified 9,322 ROHs; the litter-size traits had a significant negative correlation to FROH. A total of 3,317 CNVs, 24 CCNVR, and 50 HCNVR were identified using cnvPartition and PennCNV. Eleven genes related to reproduction were identified in CCNVRs, including seven genes related to the testis and sperm function in CCNVR1 (chr1 from 311585283 to 315307620). Two candidate genes (NEURL1 and SH3PXD2A) related to reproduction traits were identified in HCNVR34. The result suggests that these genes may improve the litter size of Bama Xiang by marker-assisted selection. However, attention should be paid to deter inbreeding in Bama Xiang pigs to conserve their genetic diversity.

Evolution of a New Testis-Specific Functional Promoter Within the Highly Conserved Map2k7 Gene of the Mouse

Map2k7 (synonym Mkk7) is a conserved regulatory kinase gene and a central component of the JNK signaling cascade with key functions during cellular differentiation. It shows complex transcription patterns, and different transcript isoforms are known in the mouse (Mus musculus). We have previously identified a newly evolved testis-specific transcript for the Map2k7 gene in the subspecies M. m. domesticus. Here, we identify the new promoter that drives this transcript and find that it codes for an open reading frame (ORF) of 50 amino acids. The new promoter was gained in the stem lineage of closely related mouse species but was secondarily lost in the subspecies M. m. musculus and M. m. castaneus. A single mutation can be correlated with its transcriptional activity in M. m. domesticus, and cell culture assays demonstrate the capability of this mutation to drive expression. A mouse knockout line in which the promoter region of the new transcript is deleted reveals a functional contribution of the newly evolved promoter to sperm motility and the spermatid transcriptome. Our data show that a new functional transcript (and possibly protein) can evolve within an otherwise highly conserved gene, supporting the notion of regulatory changes contributing to the emergence of evolutionary novelties.

Biological Roles of Lipocalins in Chemical Communication, Reproduction, and Regulation of Microbiota

Major evolutionary transitions were always accompanied by genetic remodelling of phenotypic traits. For example, the vertebrate transition from water to land was accompanied by rapid evolution of olfactory receptors and by the expansion of genes encoding lipocalins, which - due to their transporting functions - represent an important interface between the external and internal organic world of an individual and also within an individual. Similarly, some lipocalin genes were lost along other genes when this transition went in the opposite direction leading, for example, to cetaceans. In terrestrial vertebrates, lipocalins are involved in the transport of lipophilic substances, chemical signalling, odour reception, antimicrobial defence and background odour clearance during ventilation. Many ancestral lipocalins have clear physiological functions across the vertebrate taxa while many other have - due to pleiotropic effects of their genes - multiple or complementary functions within the body homeostasis and development. The aim of this review is to deconstruct the physiological functions of lipocalins in light of current OMICs techniques. We concentrated on major findings in the house mouse in comparison to other model taxa (e.g., voles, humans, and birds) in which all or most coding genes within their genomes were repeatedly sequenced and their annotations are sufficiently informative.

Epididymal initial segment-specific Cre recombinase activity in Lcn8-Cre knock-in mice

BACKGROUND

Sperm acquire the ability to fertilize ova through a complex process of epididymal maturation. To identify the functions of genes expressed in the proximal epididymis, mouse models specific to this region are needed.

METHODS AND RESULTS

A Lcn8-Cre knock-in mouse line was generated using CRISPR/Cas9 technology. A 37 bp coding sequence of Lcn8 from the ATG start codon was replaced by an NLS-Cre-polyA cassette, resulting in Cre expression and the absence of Lcn8. Epididymal initial segment-specific Cre expression was identified using RT-PCR and western blotting, and the spatial-temporal Cre activity was further confirmed by using the Rosa26^tdTomato reporter mice. Immunofluorescence staining showed that active Cre recombinase was present in the principal cells. Histological analyses of sperm and epididymides, and the four-month mating tests, were used to confirm that Cre expression did not affect normal development and male fecundity.

CONCLUSIONS

The novel Lcn8-Cre mice can be used to establish epididymal initial segment-specific conditional knock-out mouse models.

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.