Molecular Markers of Spermatogonial Stem Cells in the Domestic Cat

UCHL1 maintains microenvironmental homeostasis in goat germline stem cells

Spermatogonial stem cells (SSCs) play a crucial role in mammalian spermatogenesis and maintain the stable inheritance of the germline in livestock. However, stress and bacterial or viral infections can disrupt immune homeostasis of the testes, thereby leading to spermatogenesis destruction and infertility, which severely affects the health and productivity of mammals. This study aimed to explore the effect of ubiquitin C-terminal hydrolase L1 (UCHL1) knockdown (KD) in goat SSCs and mouse testes and investigate the potential anti-inflammatory function of UCHL1 in a poly(I:C)-induced inflammation model to maintain microenvironmental homeostasis. In vitro, the downregulation of UCHL1 (UCHL1 KD) in goat SSCs increased the expression levels of apoptosis and inflammatory factors and inhibited the self-renewal and proliferation of SSCs. In vivo, the structure of seminiferous tubules and spermatogenic cells was disrupted after UCHL1 KD, and the expression levels of apoptosis- and inflammation-related proteins were significantly upregulated. Furthermore, UCHL1 inhibited the TLR3/TBK1/IRF3 pathway to resist poly(I:C)-induced inflammation in SSCs by antagonizing HSPA8 and thus maintaining SSC autoimmune homeostasis. Most importantly, the results of this study showed that UCHL1 maintained immune homeostasis of SSCs and spermatogenesis. UCHL1 KD not only inhibited the self-renewal and proliferation of goat SSCs and spermatogenesis but was also involved in the inflammatory response of goat SSCs. Additionally, UCHL1 has an antiviral function in SSCs by antagonizing HSPA8, which provides an important basis for exploring the specific mechanisms of UCHL1 in goat spermatogenesis.

Molecular phenotyping of domestic cat (Felis catus) testicular cells across postnatal development - A model for wild felids

Molecular characterisation of testicular cells is a pivotal step towards a profound understanding of spermatogenesis and developing assisted reproductive techniques (ARTs) based on germline preservation. To enable the identification of testicular somatic and spermatogenic cell types in felids, we investigated the expression of five molecular markers at the protein level in testes from domestic cats (Felis catus) at different developmental phases (prepubertal, pubertal I and II, postpubertal I and II) classified by single-cell ploidy analysis. Our findings indicate a prominent co-labelling for two spermatogonial markers, UCHL1 and FOXO1, throughout postnatal testis development. Smaller subsets of UCHL1 or FOXO1 single-positive spermatogonia were also evident, with the FOXO1 single-positive spermatogonia predominantly observed in prepubertal testes. As expected, DDX4+ germ cells increased in numbers beginning in puberty, reaching a maximum at adulthood (post-pubertal phase), corresponding to the sequential appearance of labelled spermatogonia, spermatocytes and spermatids. Furthermore, we identified SOX9+ Sertoli cells and CYP17A1+ Leydig cells in all of the developmental groups. Importantly, testes of African lion (Panthera leo), Sumatran tiger (Panthera tigris sumatrae), Chinese leopard (Panthera pardus japonesis) and Sudan cheetah (Acinonyx jubatus soemmeringii) exhibited conserved labelling for UCHL1, FOXO1, DDX4, SOX9 and CYP17A1. The present study provides fundamental information about the identity of spermatogenic and somatic testicular cell types across felid development that will be useful for developing ART approaches to support endangered felid conservation.

Reproductive stage- and season-dependent culture characteristics of enriched caprine male germline stem cells

The present study aims to evaluate season- and reproductive-stage dependent variation in culture characteristics and expression of pluripotency and adhesion markers in caprine-male germline stem cells (cmGSCs). For this, testes from pre-pubertal (4-6 months) and adult (~ 2 years) bucks during non-breeding (July-August; n = 4 each) and breeding (October-November; n = 4 each) seasons were used to isolated testicular cells by two-step enzymatic digestion. After cmGSCs enrichment by multiple methods (differential platting, Percoll density gradient centrifugation, and MACS), cell viability of CD90⁺ cells was assessed before co-cultured onto the Sertoli cell feeder layer up to 3^rd-passage (P-3). The culture characteristics of cmGSCs were compared during primary culture (P-0) and P-3 with different assays [BrdU-assay (proliferation), MTT-assay (senescence), and Cluster-forming activity-assay] and transcript expression analyses by qRT-PCR. Moreover, the co-localization of UCHL-1, CD90, and DBA was examined by a double-immunofluorescence method. In adult bucks, significantly (p < 0.05) higher cell numbers with the ability to proliferate faster and form a greater number of cell clusters, besides up-regulation of pluripotency and adhesion markers expression were observed during the breeding season than the non-breeding season. In contrast, such season-dependent variation was lacking in pre-pubertal bucks. The expression of transcripts during non-breeding seasons was significantly (p < 0.05) higher in pre-pubertal cmGSCs than in adult cells (UCHL-1 = 2.38-folds; CD-90 = 6.66-folds; PLZF = 20.87-folds; ID-4 = 4.75-folds; E-cadherin = 3.89-folds and β1-integrin = 5.70-folds). Overall, the reproductive stage and season affect the population, culture characteristics, and expression of pluripotency and adhesion specific markers in buck testis. These results provide an insight to develop an efficient system for successful cell culture processes targeting cmGSCs.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10616-021-00515-x.

Endogenous pluripotent factor expression after reprogramming cat fetal fibroblasts using inducible transcription factors

Incomplete transgene-silencing remains a challenge in the generation of induced pluripotent stem cells (iPSC) in felids-a critical family in biomedical and biodiversity conservation science. In this study doxycycline-inducible transgenes (NANOG, POU5F1, SOX2, KLF4, and cMYC) were used to reprogram cat fetal fibroblasts with the objective of obtaining iPSC with fully silenced transgenes. Colony formation was slower (14 vs. 8 days) and at lower efficiency than mouse embryonic fibroblasts (0.002% vs. 0.02% of seeded cells). Alkaline-phosphatase positive colonies were grown on feeder cells plus LIF and GSK3, MEK, and ROCK inhibitors. Cells could be passaged singly and transgene expression was silenced at passage 3 (P3) after doxycycline removal at P2. NANOG, POU5F1, and SOX2 were expressed at P3, P6, and P10, although at lower immunostaining intensities than in cat inner cell masses (ICM). Transcripts related to pluripotency (NANOG, POU5F1, SOX2, KLF4, cMYC, and REX1) and differentiation (FGF5, TBXT, GATA6, SOX17, FOXF1, PAX6, and SOX1) were assessed by a reverse transcription-quantitative polymerase chain reaction in iPSC and embryoid bodies. The immunostaining patterns, relatively low levels of NANOG and REX1 in comparison to ICM along with the expression of TBXT (mesoderm) suggested that cells were a mix of reprogrammed pluripotent and differentiating cells.

Influence of warming and reanimation conditions on seminiferous tubule morphology, mitochondrial activity, and cell composition of vitrified testicular tissues in the domestic cat model

Understanding critical roles of warming and reanimation is critical to improve the survival of vitrified testicular tissue in domestic cats. The objective was to study structural and functional properties of testicular tissues from prepubertal domestic cats after standard vitrification followed by two warming protocols (directly at 37°C or with a 5-second pre-exposure to 50°C) and three reanimation time points (immediately, 24 h and 5 days post-warming). In Experiment 1, tissues were evaluated for histo-morphology and mitochondrial activity immediately or 24 h after warming protocols. In Experiment 2, cell viability, DNA fragmentation, and germ cell composition were assessed immediately, 24 h, or 5 days after optimal warming. Preservation of seminiferous tubule structure was better using warming at 50°C for five seconds, and survival of somatic as well as germinal cells was higher compared to direct warming at 37°C for one minute. Short term in vitro culture (for reanimation) also proved that cellular composition and functionality were better preserved when warmed for a short time at 50°C. Collective data showed that short warming at 50°C led to better quality of seminiferous tubule structure and cell composition after vitrification and short-term culture. In addition, data suggest clear directions to further understand and optimize testicular tissue survival after fertility preservation procedures.

Can we induce spermatogenesis in the domestic cat using an in vitro tissue culture approach?

The reduced number of animals in most wild felid populations implies a loss of genetic diversity. The death of juveniles, prior to the production of mature sperm, represents a loss of potential genetic contribution to future populations. Since 2011 mouse testicular organ culture has introduced an alternative mechanism to produce sperm in vitro from immature tissue. However, extension of this technology to other species has remained limited. We have used the domestic cat (Felis catus) as a model for wild felids to investigate spermatogenesis initiation and regulation, with the mouse serving as a control species. Testicular tissue fragments were cultured in control medium or medium supplemented with knockout serum replacement (KSR), AlbuMax, beta-estradiol or AlbuMax plus beta-estradiol. Contrary to expectations, and unlike results obtained in mouse controls, no germ cell differentiation could be detected. The only germ cells observed after six weeks of culture were spermatogonia regardless of the initial stage of tubule development in the donor tissue. Moreover, the number of spermatogonia decreased with time in culture in all media tested, especially in the medium supplemented with KSR, while AlbuMax had a slight protective effect. The combination of AlbuMax and beta-estradiol led to an increase in the area occupied by seminiferous tubules, and thus to an increase in total number of spermatogonial cells. Considering all the media combinations tested the stimulus for felid germ cell differentiation in this type of system seems to be different from the mouse. Studies using other triggers of differentiation and tissue survival factors should be performed to pursue this technology for the genetic diversity preservation in wild felids.

Molecular markers of putative spermatogonial stem cells in the domestic cat

Spermatogonial stem cells (SSCs) are an important tool for fertility preservation and species conservation. The ability to expand SSCs by in vitro culture is a crucial premise for their use in assisted reproduction. Because SSCs represent a small proportion of the germ cells in the adult testis, culture success is aided by pre-enrichment through sorting techniques based on cell surface-specific markers. Given the importance of the domestic cat as a model for conservation of endangered wild felids, herein we sought to examine culture conditions as well as molecular markers for cat SSCs. Using a cell culture medium for mouse SSCs supplemented with glial cell-derived neurotrophic factor (GDNF), germ cells from prepuberal cat testes remained viable in culture for up to 43 days. Immunohistochemistry for promyelocytic leukaemia zinc finger (PLZF) protein on foetal, prepuberal and adult testis sections revealed a pattern of expression consistent with the labelling of undifferentiated spermatogonia. Fluorescence-activated cell sorting (FACS) with an antibody against epithelial cell adhesion molecule (EPCAM) was used to sort live cells. Then, the gene expression profile of EPCAM-sorted cells was investigated through RT-qPCR. Notably, EPCAM (+) cells expressed relatively high levels of CKIT (CD117), a surface protein typically expressed in differentiating germ cells but not SSCs. Conversely, EPCAM (-) cells expressed relatively high levels of POU domain class 5 transcription factor 1 (POU1F5 or OCT4), clearly a germ line stem cell marker. These results suggest that cat SSCs would probably be found within the population of EPCAM (-) cells. Future studies should identify additional surface markers that alone or in combination can be used to further enrich SSCs from cat germ cells.

Immunolocalization of proteins in the spermatogenesis process of canine

Spermatogenesis is a process in which differentiated cells are produced and the adult stem cell population-known as spermatogonial stem cells (SSCs)-is continuously replenished. However, the molecular mechanisms underlying these processes are not fully understood in the canine species. We addressed this in this study by analysing the expression of specific markers in spermatogonia of seminiferous tubules of canine testes. SSCs at different stages of reproductive development (prepubertal and adult) were examined by immunohistochemistry and flow cytometry. Glial cell-derived neurotrophic factor family receptor alpha-1 (GFRA1), deleted in azoospermia-like (DAZL) and promyelocytic leukaemia zinc finger (PLZF) were expressed in SSCs, while stimulated by retinoic acid gene 8 (STRA8) was detected only in undifferentiated spermatogonia in prepubertal testis and differentiated spermatogonia and spermatocytes in adult canine. Octamer-binding transcription factor 4 (OCT4) showed an expression pattern, and the levels did not differ between the groups examined. However, C-kit expression varied as a function of reproductive developmental stage. Our results demonstrate that these proteins play critical roles in the self-renewal and differentiation of SSCs and can serve as markers to identify canine spermatogonia at specific stages of development.

Conservation of spermatogonial stem cell marker expression in undifferentiated felid spermatogonia

Spermatogonial stem cells (SSCs) are distinct in their ability to self-renew, transmit genetic information, and persist throughout the life of an individual. These characteristics make SSCs a useful tool for addressing diverse challenges such as efficient transgenic production in nonrodent, biomedical animal models, or preservation of the male genome for species in which survival of frozen-thawed sperm is low. A requisite first step to access this technology in felids is the establishment of molecular markers. This study was designed to evaluate, in the domestic cat (Felis catus), the expression both in situ and following enrichment in vitro of six genes (GFRA1, GPR125, ZBTB16, POU5F1, THY1, and UCHL1) that had been previously identified as SSC markers in other species. Antibodies for surface markers glial cell line-derived neurotrophic factor family receptor alpha 1, G protein-coupled receptor 125, and thymus cell antigen 1 could not be validated, whereas Western blot analysis of prepubertal, peripubertal, and adult cat testis confirmed protein expression for the intracellular markers ubiquitin carboxy-terminal hydrolase 1, zinc finger and BTB domain-containing protein 16, and POU domain, class 5, transcription factor 1. Colocalization of the markers by immunohistochemistry revealed that several cells within the subpopulation adjacent to the basement membrane of the seminiferous tubules and identified morphologically as spermatogonia, expressed all three intracellular markers. Studies performed on cheetah (Acinonyx jubatus) and Amur leopard (Panthera pardus orientalis) testis exhibited a conserved expression pattern in protein molecular weights, relative abundance, and localization of positive cells within the testis. The expression of the three intracellular SSC marker proteins in domestic and wild cat testes confirms conservation of these markers in felids. Enrichment of marker transcripts after differential plating was also observed. These markers will facilitate further studies in cell enrichment and IVC of felid SSCs enabling both production of transgenic domestic cats and preservation of the male genome from rare and endangered felids.

Beyond the mouse monopoly: studying the male germ line in domestic animal models

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis and essential to maintain the continuous production of spermatozoa after the onset of puberty in the male. The study of the male germ line is important for understanding the process of spermatogenesis, unravelling mechanisms of stemness maintenance, cell differentiation, and cell-to-cell interactions. The transplantation of SSCs can contribute to the preservation of the genome of valuable individuals in assisted reproduction programs. In addition to the importance of SSCs for male fertility, their study has recently stimulated interest in the generation of genetically modified animals because manipulations of the male germ line at the SSC stage will be maintained in the long term and transmitted to the offspring. Studies performed mainly in the mouse model have laid the groundwork for facilitating advancements in the field of male germ line biology, but more progress is needed in nonrodent species in order to translate the technology to the agricultural and biomedical fields. The lack of reliable markers for isolating germ cells from testicular somatic cells and the lack of knowledge of the requirements for germ cell maintenance have precluded their long-term maintenance in domestic animals. Nevertheless, some progress has been made. In this review, we will focus on the state of the art in the isolation, characterization, culture, and manipulation of SSCs and the use of germ cell transplantation in domestic animals.