Flow cytometric method to isolate round spermatids from mouse testis

Use of assisted reproductive technologies (ARTs) to shorten the generational interval in ruminants: current status and perspectives

The challenges posed by climate change and increasing world population are stimulating renewed efforts for improving the sustainability of animal production. To meet such challenges, the contribution of genomic selection approaches, in combination with assisted reproductive technologies (ARTs), to spreading and preserving animal genetics is essential. The largest increase in genetic gain can be achieved by shortening the generation interval. This review provides an overview of the current status and progress of advanced ARTs that could be applied to reduce the generation time in both female and male of domestic ruminants. In females, the use of juvenile in vitro embryo transfer (JIVET) enables to generate offspring after the transfer of in vitro produced embryos derived from oocytes of prepubertal genetically superior donors reducing the generational interval and acceleration genetic gain. The current challenge is increasing in vitro embryo production (IVEP) from prepubertal derived oocytes which is still low and variable. The two main factors limiting IVEP success are the intrinsic quality of prepubertal oocytes and the culture systems for in vitro maturation (IVM). In males, advancements in ARTs are providing new strategies to in vitro propagate spermatogonia and differentiate them into mature sperm or even to recapitulate the whole process of spermatogenesis from embryonic stem cells. Moreover, the successful use of immature cells, such as round spermatids, for intracytoplasmic injection (ROSI) and IVEP could allow to complete the entire process in few months. However, these approaches have been successfully applied to human and mouse whereas only a few studies have been published in ruminants and results are still controversial. This is also dependent on the efficiency of ROSI that is limited by the current isolation and selection protocols of round spermatids. In conclusion, the current efforts for improving these reproductive methodologies could lead toward a significant reduction of the generational interval in livestock animals that could have a considerable impact on agriculture sustainability.

Exosome-derived Small RNAs in mouse Sertoli cells inhibit spermatogonial apoptosis

Spermatogenesis is a highly complicated biological process that occurs in the epithelium of the seminiferous tubules. It is regulated by a complex network of endocrine and paracrine factors. Sertoli cells (SCs) play a key role in spermatogenesis due to their production of trophic, differentiation, and immune-modulating factors. However, many of the molecular pathways of SC action remain controversial and unclear. Recently, many studies have focused on exosomes as an important mechanism of intercellular communication. We found that the exosomes derived from mouse SCs inhibited the apoptosis of primary spermatogonia. A total of 1016 miRNAs in SCs and 556 miRNAs in exosomes were detected using miRNA high-throughput sequencing. A total of 294 miRNAs were differentially expressed between SCs and exosomes. Furthermore, 19 tsRNA families appeared in SCs, while 6 tsRNA families appeared in exosomes. A total of 57 and 1 miRNAs (RPM >4) and 14 and 1 tsRNAs were exclusively expressed in SCs and exosomes, respectively. MiR-10b is one of the top ten exosomes with a relatively large enrichment of miRNA. Overexpression of miR-10b downregulates the expression of the target KLF4 to reduce spermatogonial apoptosis in primary spermatogonia or the C18-4 cell line.

Predicted gene 31453 (Gm31453) and the gene encoding carboxypeptidase A5 (Cpa5) are not essential for spermatogenesis and male fertility in the mouse

Numerous long non-coding (lnc) RNAs are highly enriched or exclusively expressed in the mammalian testis, even in spermatids. Spermatid perinuclear RNA-binding protein (STRBP) can bind many RNAs, and loss of STRBP impairs male fertility. However, the functions of lncRNAs interacting with STRBP are unknown. In this study, the roles of one STRBP-interacting lncRNA, namely predicted gene 31453 (Gm31453), and its potential target gene encoding carboxypeptidase A5 (Cpa5) in spermatogenesis were determined using gene-knockout (KO) mice. Gm31453 and Cpa5 are located adjacent to each other on the same chromosome and are highly expressed in the testis. Gm31453 and Cpa5 are primarily expressed from secondary spermatocytes to elongated spermatids, implying their involvement in spermiogenesis. Although deletion of Gm31453 disturbed the expression of both its target and interacting gene, as indicated by decreased Cpa5 and increased Strbp mRNA levels, both Gm31453- and Cpa5-KO mice showed normal spermatogenesis and fertility, and had no detectable abnormalities in terms of testicular and epididymal development, sperm production morphology or motility, pregnancy rate or litter size. Thus, Gm31453 and Cpa5 are dispensable for spermatogenesis and male fertility in mice. Their involvement in spermatogenesis may be a fine-tuning role, regulating gene expression at the molecular level.

Infertility Caused by Inefficient Apoptotic Germ Cell Clearance in Xkr8-Deficient Male Mice

During spermatogenesis, up to 75% of germ cells in the testes undergo apoptosis and are cleared by Sertoli cells. X-linked XK blood group-related 8 (Xkr8) is a plasma membrane protein that scrambles phospholipids in response to apoptotic signals, exposing phosphatidylserine (PtdSer). Here, we found that Xkr8 ^-/- male mice were infertile due to reduced sperm counts in their epididymides. Apoptotic stimuli could not induce PtdSer exposure in Xkr8 ^-/- germ cells. Consistent with the hypothesis that PtdSer functions as an "eat-me" signal to phagocytes, cells expressing phosphatidylserine receptor TIM4 and MER tyrosine kinase receptor efficiently engulfed apoptotic wild-type male germ cells but not Xkr8 ^-/- germ cells. Fluorescence and electron microscopy revealed Sertoli cells carrying engulfed and degenerated dead cells. However, many unengulfed apoptotic cells and residual bodies and much cell debris were present in Xkr8 ^-/- testes and epididymides. These results indicate that Xkr8-mediated PtdSer exposure is essential for the clearance of apoptotic germ cells by Sertoli cells. There was no apparent inflammation in Xkr8 ^-/- testes, suggesting that the unengulfed apoptotic cells may have undergone secondary necrosis, releasing noxious materials that affected the germ cells. Alternatively, failure to engulf the apoptotic germ cells may have caused the Sertoli cells to starve and lose their ability to support spermatogenesis.

Single-cell RNA sequencing of adult mouse testes

Spermatogenesis is an efficient and complex system of continuous cell differentiation. Previous studies investigating the transcriptomes of different cell populations in the testis relied either on sorting cells, cell depletion, or juvenile animals where not all stages of spermatogenesis have been completed. We present single-cell RNA sequencing (scRNA-Seq) data of 2,500 cells from the testes of two 8-week-old C57Bl/6J mice. Our dataset includes all spermatogenic stages from preleptotene to condensing spermatids as well as individual spermatogonia, Sertoli and Leydig cells. The data capture the full continuity of the meiotic and postmeiotic stages of spermatogenesis, and is thus ideally suited for marker discovery, network inference and similar analyses for which temporal ordering of differentiation processes can be exploited. Furthermore, it can serve as a reference for future studies involving single-cell RNA-Seq in mice where spermatogenesis is perturbed.

RChIP-Seq: Chromatin-Associated RNA Sequencing in Developmentally Staged Mouse Testes

Chromatin is a dynamic macromolecular structure comprised of histones and a wealth of non-histone proteins. Recently, it has become clear that RNA is also an integral component of chromatin playing an important role in regulating its structure and function. Central to the understanding of RNA function is the ability to identify and genomically map interactions between chromatin components and RNA.Here, we describe a new method, RChIP-seq (RNA-associated-Chromatin-Immuno Precipitation followed by next-generation sequencing) that allows the identification of RNA species that are directly bound to specific components of chromatin in the mouse testis.

Characterization of germ cell differentiation in the male mouse through single-cell RNA sequencing

Spermatogenesis in the mouse has been extensively studied for decades. Previous methods, such as histological staining or bulk transcriptome analysis, either lacked resolution at the single-cell level or were focused on a very narrowly defined set of factors. Here, we present the first comprehensive, unbiased single-cell transcriptomic view of mouse spermatogenesis. Our single-cell RNA-seq (scRNA-seq) data on over 2,500 cells from the mouse testis improves upon stage marker detection and validation, capturing the continuity of differentiation rather than artificially chosen stages. scRNA-seq also enables the analysis of rare cell populations masked in bulk sequencing data and reveals new insights into the regulation of sex chromosomes during spermatogenesis. Our data provide the basis for further studies in the field, for the first time providing a high-resolution reference of transcriptional processes during mouse spermatogenesis.

Transcriptomic Variation during Spermiogenesis in Mouse Germ Cells

To explore variations in the transcription activity during spermiogenesis, round and elongated spermatids were collected from ICR/CD1 model mice using laser capture microdissection (LCM) and cauda epididymal sperm samples. The transcripts were sequenced using RNA-seq, and the reads were mapped to mm9. The majority of the reads (70%) in the round and elongated spermatids were mappable to known and predicted exons, but that in sperm was only 9%. The results of the distribution of reads suggested that alternative splicing was more complicated in sperm than in round and elongated spermatids. In the 19,127 genes, we detected the expression of 5,104 de novo genes and 91,112 alternative splicing events, and 12,105 were differentially expressed. Gene ontology (GO), InterPro domains, and KEGG revealed changes in gene transcription, mitochondrial protein translation, cellular components, and energy metabolism during spermiogenesis. The results provided considerable information about alternative splicing events, differentiallly expressed genes (DEGs), and novel transcriptions during spermiogenesis in mice.

Step-specific Sorting of Mouse Spermatids by Flow Cytometry

The differentiation of mouse spermatids is one critical process for the production of a functional male gamete with an intact genome to be transmitted to the next generation. So far, molecular studies of this morphological transition have been hampered by the lack of a method allowing adequate separation of these important steps of spermatid differentiation for subsequent analyses. Earlier attempts at proper gating of these cells using flow cytometry may have been difficult because of a peculiar increase in DNA fluorescence in spermatids undergoing chromatin remodeling. Based on this observation, we provide details of a simple flow cytometry scheme, allowing reproducible purification of four populations of mouse spermatids fixed with ethanol, each representing a different state in the nuclear remodeling process. Population enrichment is confirmed using step-specific markers and morphological criterions. The purified spermatids can be used for genomic and proteomic analyses.

RNA Binding Protein Ptbp2 Is Essential for Male Germ Cell Development

RNA binding proteins (RBPs) are increasingly recognized as essential factors in tissue development and homeostasis. The polypyrimidine tract binding (PTB) protein family of RBPs are important posttranscriptional regulators of gene expression. In the nervous system, the function and importance of PTB protein 2 (Ptbp2) as a key alternative splicing regulator is well established. Ptbp2 is also abundantly expressed during spermatogenesis, but its role in this developmental program has not been explored. Additionally, the importance of alternative splicing regulation in spermatogenesis is unclear. Here, we demonstrate that Ptbp2 is essential for spermatogenesis. We also describe an improved dual fluorescence flow cytometry strategy to discriminate, quantify, and collect germ cells in different stages of development. Using this approach, in combination with traditional histological methods, we show that Ptbp2 ablation results in germ cell loss due to increased apoptosis of meiotic spermatocytes and postmeiotic arrest of spermatid differentiation. Furthermore, we show that Ptbp2 is required for alternative splicing regulation in the testis, as in brain. Strikingly, not all of the alternatively spliced RNAs examined were sensitive to Ptbp2 loss in both tissues. Collectively, the data provide evidence for an important role for alternative splicing regulation in germ cell development and a central role for Ptbp2 in this process.

Characterisation of the deleted in azoospermia like (Dazl)-green fluorescent protein mouse model generated by a two-step embryonic stem cell-based strategy to identify pluripotent and germ cells

The deleted in azoospermia like (Dazl) gene is preferentially expressed in germ cells; however, recent studies indicate that it may have pluripotency-related functions. We generated Dazl-green fluorescent protein (GFP) transgenic mice and assayed the ability of Dazl-driven GFP to mark preimplantation embryo development, fetal, neonatal and adult tissues, and in vitro differentiation from embryonic stem cells (ESCs) to embryoid bodies (EBs) and to primordial germ cell (PGC)-like cells. The Dazl-GFP mice were generated by a two-step ESC-based strategy, which enabled primary and secondary screening of stably transfected clones before embryo injection. During preimplantation embryo stages, GFP was detected from the zygote to blastocyst stage. At Embryonic Day (E) 12.5, GFP was expressed in gonadal ridges and in neonatal gonads of both sexes. In adult mice, GFP expression was found during spermatogenesis from spermatogonia to elongating spermatids and in the cytoplasm of oocytes. However, GFP mRNA was also detected in other tissues harbouring multipotent cells, such as the intestine and bone marrow. Fluorescence was maintained along in vitro Dazl-GFP ESC differentiation to EBs, and in PGC-like cells. In addition to its largely known function in germ cell development, Dazl could have an additional role in pluripotency, supporting these transgenic mice as a valuable tool for the prospective identification of stem cells from several tissues.

FACS selection of valuable mutant mouse round spermatids and strain rescue via round spermatid injection

Round spermatid injection (ROSI) into mammalian oocytes can result in the development of viable embryos and offspring. One current limitation to this technique is the identification of suitable round spermatids. In the current paper, round spermatids were selected from testicular cells with phase contrast microscopy (PCM) and fluorescence-activated cell sorting (FACS), and ROSI was performed in two strains of mice. The rates of fertilization, embryonic development and offspring achieved were the same in all strains. Significantly, round spermatids selected by PCM and FACS were effectively used to rescue the infertile Pten-null mouse. The current results indicate that FACS selection of round spermatids can not only provide high-purity and viable round spermatids for use in ROSI, but also has no harmful effects on the developmental capacity of subsequently fertilized embryos. It was concluded that round spermatids selected by FACS are useful for mouse strain rederivation and rescue of infertile males; ROSI should be considered as a powerful addition to the armamentarium of assisted reproduction techniques applicable in the mouse.

Isolation of Sertoli, Leydig, and spermatogenic cells from the mouse testis

A thorough understanding of the events during mammalian spermatogenesis requires studying specific molecular signatures of individual testicular cell populations as well as their interaction in co-cultures. However, most purification techniques to isolate specific testicular cell populations are time-consuming, require large numbers of animals, and/or are only able to isolate a few cell types. Here we describe a cost-effective and timesaving approach that uses a single protocol to enrich multiple testicular cell populations (Sertoli, Leydig, and several spermatogenic cell populations) from as few as one mouse. Our protocol combines rigorous enzymatic digestion of seminiferous tubules with counter-current centrifugal elutriation, yielding specific testicular cell populations with >80%-95% purity.

High-purity flow sorting of early meiocytes based on DNA analysis of guinea pig spermatogenic cells

Mammalian spermatogenesis is still nowadays poorly understood at the molecular level. Testis cellular heterogeneity is a major drawback for spermatogenic gene expression studies, especially when research is focused on stages that are usually very short and poorly represented at the cellular level such as initial meiotic prophase I (i.e., leptotene [L] and zygotene [Z]). Presumably, genes whose products are involved in critical meiotic events such as alignment, pairing and recombination of homologous chromosomes are expressed during the short stages of early meiotic prophase. Aiming to characterize mammalian early meiotic gene expression, we have found the guinea pig (Cavia porcellus) as an especially attractive model. A detailed analysis of its first spermatogenic wave by flow cytometry (FCM) and optical microscopy showed that guinea pig testes exhibit a higher representation of early meiotic stages compared to other studied rodents, partly because of their longer span, and also as a result of the increased number of cells entering meiosis. Moreover, we have found that adult guinea pig testes exhibit a peculiar 4C DNA content profile, with a bimodal peak for L/Z and P spermatocytes that is absent in other rodents. Besides, we show that this unusual 4C peak allows the separation by FCM of highly pure L/Z spermatocyte populations aside from pachytene ones, even from adult individuals. To our knowledge, this is the first report on an accurate and suitable method for highly pure early meiotic prophase cell isolation from adult mammals, and thus sets an interesting approach for gene expression studies aiming at a deeper understanding of the molecular groundwork underlying male gamete production.

ETV5 regulates sertoli cell chemokines involved in mouse stem/progenitor spermatogonia maintenance

Spermatogonial stem cells are the only stem cells in the body that transmit genetic information to offspring. Although growth factors responsible for self-renewal of these cells are known, the factors and mechanisms that attract and physically maintain these cells within their microenvironment are poorly understood. Mice with targeted disruption of Ets variant gene 5 (Etv5) show total loss of stem/progenitor spermatogonia following the first wave of spermatogenesis, resulting in a Sertoli cell-only phenotype and aspermia. Microarray analysis of primary Sertoli cells from Etv5 knockout (Etv5(-/-)) versus wild-type (WT) mice revealed significant decreases in expression of several chemokines. Chemotaxis assays demonstrated that migration of stem/progenitor spermatogonia toward Etv5(-/-) Sertoli cells was significantly decreased compared to migration toward WT Sertoli cells. Interestingly, differentiating spermatogonia, spermatocytes, and round spermatids were not chemoattracted by WT Sertoli cells, whereas stem/progenitor spermatogonia showed a high and significant chemotactic index. Rescue assays using recombinant chemokines indicated that C-C-motif ligand 9 (CCL9) facilitates Sertoli cell chemoattraction of stem/progenitor spermatogonia, which express C-C-receptor type 1 (CCR1). In addition, there is protein-DNA interaction between ETV5 and Ccl9, suggesting that ETV5 might be a direct regulator of Ccl9 expression. Taken together, our data show for the first time that Sertoli cells are chemoattractive for stem/progenitor spermatogonia, and that production of specific chemokines is regulated by ETV5. Therefore, changes in chemokine production and consequent decreases in chemoattraction by Etv5(-/-) Sertoli cells helps to explain stem/progenitor spermatogonia loss in Etv5(-/-) mice.

Fluorescence activated cell sorting of live female germ cells and somatic cells of the mouse fetal gonad based on forward and side scattering

Analysis of female mammalian germ cells has been hindered by difficulties in isolating high purity germ cell populations from embryonic and fetal gonads. Meiotic prophase stage oocytes are particularly difficult to isolate due to the lack of suitable surface markers. Oct4 promoter driven GFP expression has been used to distinguish germ cells/oocytes (GFP positive) from somatic cells (GFP negative), however, the requirement for transgenic animals has limited the use of this technique. We analyzed the side- and forward scattering properties of living cell populations obtained from fetal ovaries of Oct4-GFP transgenic and wild-type mice. On the basis of these measurements, we defined criteria that allow the discrimination and identification of germ cells and somatic cells within cell suspensions of nontransgenic female fetal gonads. The described method is suitable for the isolation of populations of germ cells and somatic cells of higher than 90% purity. We also demonstrated that the sorted cells can be used in downstream immunofluorescence and RT-PCR applications. Hence, we conclude that side and forward scattering based sorting of female germ cells is a valuable tool that will benefit the understanding of female gametogenesis.

Mili interacts with tudor domain-containing protein 1 in regulating spermatogenesis

Piwi proteins are essential for germline development, stem cell self-renewal, epigenetic regulation, and transposon silencing [1-7]. They bind to a complex class of small noncoding RNAs called Piwi-interacting RNAs (piRNAs) [8]. Mammalian Piwi proteins such as Mili are localized in the cytoplasm of spermatogenic cells, where they are associated with a germline-specific organelle called the nuage or its derivative, the chromatoid body, as well as with polysomes [9]. To investigate the molecular mechanisms mediated by Mili, we searched for Mili-interacting proteins. Here, we report that Mili specifically interacts with Tudor domain-containing protein 1 (Tdrd1), a germline protein that contains multiple Tudor domains [10, 11]. This RNA-independent interaction is mediated through the N-terminal domain of Mili and the N-terminal region of Tdrd1 containing the myeloid Nervy DEAF-1 (MYND) domain and the first two Tudor domains. In addition, Mili positively regulates the expression of the Tdrd1 mRNA. Furthermore, Mili and Tdrd1 mutants share similar spermatogenic defects. However, Tdrd1, unlike Mili, is not required for piRNA biogenesis. Our results suggest that Mili interacts with Tdrd1 in the nuage and chromatoid body. This interaction does not contribute to piRNA biogenesis but represents a regulatory mechanism that is critical for spermatogenesis.

Identification, characterization and co-localization of label-retaining cell population in mouse endometrium with typical undifferentiated markers

BACKGROUND

The endometrium, lining of the uterus, is a highly active organ that is remodelled periodically during the lifespan. Different studies suggest the presence of an adult or progenitor stem cell (PSC) population in this tissue because of its cyclic regenerative capacity.

METHODS

In this study, we aim at identifying and localizing the putative PSC population in the murine uterus using the 5-bromo-2'-deoxyuridine (BrdU) labelling method to detect label-retaining cells (LRCs) that cycle slowly. Uteri from BrdU-treated mice were analysed via single and double immunohistochemistry to co-localize them with the markers of undifferentiation already described such as c-KIT and POU5F1 (also known as OCT-4). Finally, we confirmed the presence of the indicated markers at mRNA level.

RESULTS

We observed the presence and gradual decrease of LRCs in the endometrium during the lifespan of the mice. In adulthood, the LRC population decreased notably and remained in the lower region of the stroma in the murine endometrium. Some of the endometrial LRCs co-localized with c-KIT and POU5F1. PCR and nested-PCR confirmed the presence of these undifferentiated markers.

CONCLUSIONS

We demonstrated that the murine endometrium possesses LRCs with the features of a putative PSC population localized at the lower region of the stroma.

Flow cytometric characterization of viable meiotic and postmeiotic cells by Hoechst 33342 in mouse spermatogenesis

BACKGROUND

Spermatogenesis in adult is a complex stepwise process leading to terminally differentiated spermatozoa. The cellular heterogeneity of testis renders complex the studies on molecular aspects of this differentiation process. Analysis of the regulation of adult spermatogenesis would undoubtedly benefit from the development of techniques to characterize each germinal differentiation step.

METHODS

Hoechst 33342 staining of mouse testicular cells allows characterization of an enriched population in germinal stem cell and spermatogonia, called side population. In this study, we examined the definition of the various germinal populations stained by Hoechst 33342, notably meiotic and postmeiotic cells.

RESULTS

Preleptotene spermatocytes, spermatocyte I, spermatocyte II, and round and elongated spermatids were discriminated by Hoechst 33342 staining. In addition, we associated differentiation of spermatocyte I through leptotene to diplotene with changes in Hoechst 33342 red fluorescence pattern.

CONCLUSIONS

Hoechst 33342 staining of viable germinal cells constitutes a valuable tool to study normal and impaired mouse adult spermatogenesis or to isolate viable cells from various differentiation stages for studies of molecular mechanisms regulating spermatogenesis.

Isolation and viability of presumptive spermatids collected from bull testes by Percoll density gradient

The objective of the present study was to develop a procedure for isolating pure populations of round spermatid(s) (RS) by Percoll density gradient from bull testes. Bull testes were de-capsulated and testicular tissues were dissociated enzymatically to recover RS. After being filtered through a 20 microm nylon mesh, the cells were centrifuged at 650 x g for 25 min through the discontinuous Percoll density gradients (20, 35, 40, 45 and 90% Percoll solution). Isolated cells were analyzed by microscopic observation for survivability and apoptosis. In Experiment 1, both microscopic observation and DNA analysis by flow cytometry showed that approximately 40% of cells collected from 35% Percoll gradient were presumptive RS, whereas in 40% Percoll gradient, mostly primary spermatocytes were observed. Experiment 2 compared the effect of 35% Percoll density isolation on the incidence of apoptosis and necrosis in fresh and frozen-thawed cells to those of untreated cells. The percentage (mean+/-S.E.M.) of necrosis in cells collected from 35% Percoll gradient was less (P<0.05) than in untreated and frozen-thawed cells from 35% Percoll gradient (11.7+/-3.1% compared with 26.3+/-2.0% and 53.5+/-1.3%, respectively), but the rate of apoptosis did not differ (1.2+/-0.49% compared with 2.5+/-0.8% and 0.9+/-0.04%, respectively). The proportional data (mean+/-S.E.M.) of live cells in Percoll treated group were greater (P<0.05) than in untreated and frozen-thawed cells from the 35% Percoll gradient (86.7+/-3.26% compared with 70.8+/-2.73% and 41.9+/-1.69%, respectively). Experiment 3 compared the development rates of embryos injected with RS isolated from fresh and frozen-thawed cells collected with the 35% Percoll gradient to those of untreated cells, and parthenotes as control. There were no significant (P>0.05) differences in the rates of cleavage and blastocyst development between untreated fresh cells and fresh cells collected from the 35% Percoll gradient (75.4 and 10.5% compared with 82.4 and 12.8%). However, there were lesser (P<0.05) cleavage and blastocyst rates in frozen-thawed cells from the 35% Percoll gradient (51.6 and 6.3%) and parthenotes (60.7 and 4.1%) were observed. These results suggest that isolation of presumptive RS by 35% Percoll density gradient is effective in eliminating apoptotic and early necrotic cells. However, the use of RS in improving the developmental potential of embryos merits further studies.

Seminal haploid cell detection by flow cytometry in non-obstructive azoospermia: a good predictive parameter for testicular sperm extraction

BACKGROUND

Testicular sperm extraction (TESE) associated with ICSI gives patients suffering from non-obstructive azoospermia (NOA) the possibility of becoming a father. The success rate of TESE based on sperm recovery is approximately 50%, and the commonly used non-invasive parameters are not predictive enough. Only the invasive testis biopsy has a good prognostic value. The aim of this study was to evaluate the prognostic value of the detection of seminal haploid cells by flow cytometry (FCM) in order to avoid unnecessary testicular biopsy.

METHODS

For 37 NOA patients undergoing testicular biopsy, we measured testis size, serum FSH and inhibin B levels and carried out seminal cytology, seminal FCM analysis and histological examination.

RESULTS

Sperm were found in 18 biopsies. These results were correlated with cytology, FCM analysis and the histological examination. FCM was more sensitive than cytology (100 versus 59%) but less specific (67 versus 83.5%) whereas the histological observation of complete spermatogenesis appeared to be less sensitive (50%) but more specific (100%).

CONCLUSION

Detection of seminal haploid cells by FCM appears to be an interesting non-invasive technique which can predict TESE results and improve the management of NOA patients.

Developmental Regulation of Ubiquitin C-Terminal Hydrolase Isozyme Expression During Spermatogenesis in Mice

The ubiquitin pathway functions in the process of protein turnover in eukaryotic cells. This pathway comprises the enzymes that ubiquitinate/deubiquitinate target proteins and the proteasome that degrades ubiquitin-conjugated proteins. Ubiquitin C-terminal hydrolases (UCHs) are thought to be essential for maintaining ubiquitination activity by releasing ubiquitin (Ub) from its substrates. Mammalian UCH-L1 and UCH-L3 are small proteins that share considerable homology at the amino acid level. Both of these UCHs are highly expressed in the testis/ ovary and neuronal cells. Our previous work demonstrated that UCH-L1-deficient gracile axonal dystrophy (gad) mice exhibit progressively decreasing spermatogonial stem cell proliferation, suggesting that UCH isozymes in the testis function during spermatogenesis. To analyze the expression patterns of UCH isozymes during spermatogenesis, we isolated nearly homogeneous populations of spermatogonia, spermatocytes, spermatids, and Sertoli cells from mouse testes. Western blot analysis detected UCH-L1 in spermatogonia and Sertoli cells, whereas UCH-L3 was detected in spermatocytes and spermatids. Moreover, reverse transcription-polymerase chain reaction analysis of UCH isozymes showed that UCH-L1 and UCH-L4 mRNAs are expressed in spermatogonia, whereas UCH-L3 and UCH-L5 mRNAs are expressed mainly in spermatocytes and spermatids. These results suggest that UCH-L1 and UCH-L3 have distinct functions during spermatogenesis, namely, that UCH-L1 may act during mitotic proliferation of spermatogonial stem cells whereas UCH-L3 may function in the meiotic differentiation of spermatocytes into spermatids.

Cloning and sequencing of SOB3, a human gene coding for a sperm protein homologous to an antimicrobial protein and potentially involved in zona pellucida binding

We have previously characterized an 18-19 kDa cationic protein, SOB3, that was detected in the epididymis and localized within the acrosome and on the neck region of human spermatozoa. We suggested that it is involved in secondary sperm binding to the zona pellucida. The present study describes its purification to homogeneity by preparative electrophoresis and non-equilibrium pH gradient electrophoresis. Degenerate primers deduced from microsequencing were used to amplify a specific fragment from human epididymal RNA by reverse transcription-polymerase chain reaction (RT-PCR). This 164 bp fragment was extended by 5' and 3'-RACE to obtain the 548 bp full length cDNA. The open reading frame encodes a 170 amino acid protein. SOB3 is a single copy gene. It is 98% identical to prepro-FALL39 and 100% identical to CAP18, two human genes which were initially identified by screening a human bone marrow (lambda)gt11 library, and which encode an antimicrobial protein. Northern blots of human tissues revealed a 1 kb transcript in corpus and cauda epididymis only, while RT-PCR showed presence of the mRNA in the three epididymal regions and also in round spermatids. The above results suggest that SOB3 has two roles in sperm protection and fertilization, depending on its dual origin and final sperm localization.

Variation of docosahexaenoic acid content in subsets of human spermatozoa at different stages of maturation: implications for sperm lipoperoxidative damage

The oxidation of phospholipid-bound docosahexaenoic acid (DHA) has been shown to be one of the major factors that limit the motile life span of sperm in vitro. Sperm samples show high cell-to-cell variability in life span and, consequently, in susceptibility toward lipid peroxidation. Therefore, we postulated that there is also cell-to-cell variability in DHA concentration in human spermatozoa. In this study, the concentration of DHA in subsets of human spermatozoa isolated by a discontinuous Percoll density gradient was determined by gas chromatography. Four subsets of human spermatozoa were isolated using a discontinuous Percoll gradient: fraction 1 was enriched in immature germ cells and immature sperm, fractions 2 and 3 contained, mostly, immature sperm with cytoplasmic droplets, and fraction 4 contained, for the most part, morphologically normal sperm, as determined by histochemical analysis. The results indicated that there were significant differences in DHA content in sperm from all 4 fractions. DHA content in sperm from fraction 1 was 2.5-fold higher than that found in fraction 4. DHA content in mouse sperm obtained from the seminiferous tubules was 3-fold higher than that found in mouse sperm obtained from the epididymis, consistent with the findings observed in ejaculated human sperm. The results of this study indicate (i) there is cell-to-cell variability in the concentration of DHA in human sperm and (ii) that there is a net decrease in DHA content in sperm during the process of sperm maturation.