Primate spermatogenesis: new insights into comparative testicular organisation, spermatogenic efficiency and endocrine control

Melatonin Administration Enhances Testicular Volume, Testicular Blood Flow, Semen Parameters and Antioxidant Status during the Non-Breeding Season in Bafra Rams

Our objectives were to investigate the effects of exogenous melatonin on testicular volume (TV), testicular blood flow (TBF), and semen quality in Bafra rams during the non-breeding season. One group of rams (MEL, n = 5) received a 36 mg melatonin implant twice, with 30 days in between, while the other group (CON, n = 5) served as the control. TBF, TV, and semen quality parameters were determined at three-week intervals starting three weeks before until twelve weeks after the first melatonin implant. Testicular blood flow was determined in the supratesticular (STA) and marginal testicular artery (MA) using color Doppler ultrasound. Semen was collected and evaluated, and the total oxidative status (TOS) and total antioxidative status (TAS) was determined using an ELISA. The MEL group had increased (p < 0.05) TV between the sixth and twelfth week after the start of treatment. Overall, the MEL group had lower resistance and pulsatility indexes (p < 0.05) between the third and ninth week, although there was no difference (p > 0.05) between the two groups in most semen quality parameters. However, TAS concentrations increased (p < 0.05) in the MEL group compared with the CON. The results of this study show that exogenous melatonin in the non-breeding season significantly increased both TBF and TV in Bafra rams. Therefore, giving rams implants with 36 mg melatonin twice at least one month prior to the non-breeding season is expected to improve testicular size and function and reproductive capacity.

Deep Learning-Based Spermatogenic Staging in Tissue Sections of Cynomolgus Macaque Testes

The indirect assessment of adverse effects on fertility in cynomolgus monkeys requires that tissue sections of the testis be microscopically evaluated with awareness of the stage of spermatogenesis that a particular cross-section of a seminiferous tubule is in. This difficult and subjective task could very much benefit from automation. Using digital whole slide images (WSIs) from tissue sections of testis, we have developed a deep learning model that can annotate the stage of each tubule with high sensitivity, precision, and accuracy. The model was validated on six WSI using a six-stage spermatogenic classification system. Whole slide images contained an average number of 4938 seminiferous tubule cross-sections. On average, 78% of these tubules were staged with 29% in stage I-IV, 12% in stage V-VI, 4% in stage VII, 19% in stage VIII-IX, 18% in stage X-XI, and 17% in stage XII. The deep learning model supports pathologists in conducting a stage-aware evaluation of the testis. It also allows derivation of a stage-frequency map. The diagnostic value of this stage-frequency map is still unclear, as further data on its variability and relevance need to be generated for testes with spermatogenic disturbances.

The 'faulty male' hypothesis for sex-biased mutation and disease

Biological differences between males and females lead to many differences in physiology, disease, and overall health. One of the most prominent disparities is in the number of germline mutations passed to offspring: human males transmit three times as many mutations as do females. While the classic explanation for this pattern invokes differences in post-puberty germline replication between the sexes, recent whole-genome evidence in humans and other mammals has cast doubt on this mechanism. Here, we review recent work that is inconsistent with a replication-driven model of male-biased mutation, and propose an alternative, 'faulty male' hypothesis. This model proposes that males are less able to repair and/or protect DNA from damage compared to females. Importantly, we suggest that this new model for male-biased mutation may also help to explain several pronounced differences between the sexes in cancer, aging, and DNA repair. Although the detailed contributions of genetic, epigenetic, and hormonal influences of biological sex on mutation remain to be fully understood, a reconsideration of the mechanisms underlying these differences will lead to a deeper understanding of evolution and disease.

Decoding the Spermatogenesis Program: New Insights from Transcriptomic Analyses

Spermatogenesis is a complex differentiation process coordinated spatiotemporally across and along seminiferous tubules. Cellular heterogeneity has made it challenging to obtain stage-specific molecular profiles of germ and somatic cells using bulk transcriptomic analyses. This has limited our ability to understand regulation of spermatogenesis and to integrate knowledge from model organisms to humans. The recent advancement of single-cell RNA-sequencing (scRNA-seq) technologies provides insights into the cell type diversity and molecular signatures in the testis. Fine-grained cell atlases of the testis contain both known and novel cell types and define the functional states along the germ cell developmental trajectory in many species. These atlases provide a reference system for integrated interspecies comparisons to discover mechanistic parallels and to enable future studies. Despite recent advances, we currently lack high-resolution data to probe germ cell-somatic cell interactions in the tissue environment, but the use of highly multiplexed spatial analysis technologies has begun to resolve this problem. Taken together, recent single-cell studies provide an improvedunderstanding of gametogenesis to examine underlying causes of infertility and enable the development of new therapeutic interventions.

Morphologic Features and Deep Learning-Based Analysis of Canine Spermatogenic Stages

In nonclinical toxicity studies, stage-aware evaluation is often expected to assess drug-induced testicular toxicity. Although stage-aware evaluation does not require identification of specific stages, it is important to understand microscopic features of spermatogenic staging. Staging of the spermatogenic cycle in dogs is a challenging and time-consuming process. In this study, we first defined morphologic features for the eight spermatogenic stages in standard histology sections (H&E slides) of dog testes. For image analysis, we defined the key morphologic features of five stages/pooled stage groups (I-II, III-IV, V, VI-VII, and VIII). These criteria were used to develop a deep learning (DL) algorithm for staging of the spermatogenic cycle of control dog testes using whole slide images. In addition, a DL-based nucleus segmentation model was trained to detect and quantify the number of different germ cells, including spermatogonia, spermatocytes, and spermatids. Identification of spermatogenic stages and quantification of germ cell populations were successfully automated by the DL models. Combining these two algorithms provided color-coding visual spermatogenic staging and quantitative information on germ cell populations at specific stages that would facilitate the stage-aware evaluation and detection of changes in germ cell populations in nonclinical toxicity studies.

NANOS3 suppresses premature spermatogonial differentiation to expand progenitors and fine-tunes spermatogenesis in mice

In the mouse testis, sperm originate from spermatogonial stem cells (SSCs). SSCs give rise to spermatogonial progenitors, which expand their population until entering the differentiation process that is precisely regulated by a fixed time-scaled program called the seminiferous cycle. Although this expansion process of progenitors is highly important, its regulatory mechanisms remain unclear. NANOS3 is an RNA-binding protein expressed in the progenitor population. We demonstrated that the conditional deletion of Nanos3 at a later embryonic stage results in the reduction of spermatogonial progenitors in the postnatal testis. This reduction was associated with the premature differentiation of progenitors. Furthermore, this premature differentiation caused seminiferous stage disagreement between adjacent spermatogenic cells, which influenced spermatogenic epithelial cycles, leading to disruption of the later differentiation pathway. Our study suggests that NANOS3 plays an important role in timing progenitor expansion to adjust to the proper differentiation timing by blocking the retinoic acid (RA) signaling pathway.

Limited spermatogenic differentiation of testicular tissue from prepubertal marmosets (Callithrix jacchus) in an in vitro organ culture system

PURPOSE

of the research: To achieve male fertility preservation and restoration, experimental strategies for in vitro germ cell differentiation are required. The effects of two different culture conditions on in vitro maintenance and differentiation of non-human primate germ cells was studied. Three testes from three 6-month-old marmosets were cultured using a gas-liquid interphase system for 12 days. Testicular maturation in pre-culture control and samples cultured in gonadotropin and serum supplemented and non-supplemented culture samples was evaluated using Periodic Acid-Schiff (PAS) and immunohistochemical stainings.

PRINCIPLE RESULTS

Gonadotropins and serum-supplemented tissues demonstrate up to meiotic differentiation (BOULE + Pachytene spermatocyte) and advanced localization of germ cells (MAGEA4+). Moreover, complex (with gonadotropin and marmoset monkey serum) conditions induced progression in somatic cell maturation with advanced seminiferous epithelial organization, maintenance of encapsulation of cultured fragments with peritubular-myoid cells, preservation of tubular structural integrity and architecture.

MAJOR CONCLUSIONS

We report stimulation-dependent in vitro meiotic transition in non-human primate testes. This model represents a novel ex vivo approach to obtain crucial developmental progression.

The initial maturation status of marmoset testicular tissues has an impact on germ cell maintenance and somatic cell response in tissue fragment culture

Successful in vitro spermatogenesis was reported using immature mouse testicular tissues in a fragment culture approach, raising hopes that this method could also be applied for fertility preservation in humans. Although maintaining immature human testicular tissue fragments in culture is feasible for an extended period, it remains unknown whether germ cell survival and the somatic cell response depend on the differentiation status of tissue. Employing the marmoset monkey (Callithrix jacchus), we aimed to assess whether the maturation status of prepubertal and peri-/pubertal testicular tissues influence the outcome of testis fragment culture. Testicular tissue fragments from 4- and 8-month-old (n = 3, each) marmosets were cultured and evaluated after 0, 7, 14, 28 and 42 days. Immunohistochemistry was performed for identification and quantification of germ cells (melanoma-associated antigen 4) and Sertoli cell maturation status (anti-Müllerian hormone: AMH). During testis fragment culture, spermatogonial numbers were significantly reduced (P < 0.05) in the 4- but not 8-month-old monkeys, at Day 0 versus Day 42 of culture. Moreover, while Sertoli cells from 4-month-old monkeys maintained an immature phenotype (i.e. AMH expression) during culture, AMH expression was regained in two of the 8-month-old monkeys. Interestingly, progression of differentiation to later meiotic stage was solely observed in one 8-month-old marmoset, which was at an intermediate state regarding germ cell content, with gonocytes as well as spermatocytes present, as well as Sertoli cell maturation status. Although species-specific differences might influence the outcome of testis fragment experiments in vitro, our study demonstrated that the developmental status of the testicular tissues needs to be considered as it seems to be decisive for germ cell maintenance, somatic cell response and possibly the differentiation potential.

CAG repeat instability in embryonic stem cells and derivative spermatogenic cells of transgenic Huntington's disease monkey

PURPOSE

The expansion of CAG (glutamine; Q) trinucleotide repeats (TNRs) predominantly occurs through male lineage in Huntington's disease (HD). As a result, offspring will have larger CAG repeats compared to their fathers, which causes an earlier onset of the disease called genetic anticipation. This study aims to develop a novel in vitro model to replicate CAG repeat instability in early spermatogenesis and demonstrate the biological process of genetic anticipation by using the HD stem cell model for the first time.

METHODS

HD rhesus monkey embryonic stem cells (rESCs) were cultured in vitro for an extended period. Male rESCs were used to derive spermatogenic cells in vitro with a 10-day differentiation. The assessment of CAG repeat instability was performed by GeneScan and curve fit analysis.

RESULTS

Spermatogenic cells derived from rESCs exhibit progressive expansion of CAG repeats with high daily expansion rates compared to the extended culture of rESCs. The expansion of CAG repeats is cell type-specific and size-dependent.

CONCLUSIONS

Here, we report a novel stem cell model that replicates genome instability and CAG repeat expansion in in vitro derived HD monkey spermatogenic cells. The in vitro spermatogenic cell model opens a new opportunity for studying TNR instability and the underlying mechanism of genetic anticipation, not only in HD but also in other TNR diseases.

Complete spermatogenesis in intratesticular testis tissue xenotransplants from immature non-human primate

STUDY QUESTION

Can full spermatogenesis be achieved after xenotransplantation of prepubertal primate testis tissue to the mouse, in testis or subcutaneously?

SUMMARY ANSWER

Intratesticular xenotransplantation supported the differentiation of immature germ cells from marmoset (Callithrix jacchus) into spermatids and spermatozoa at 4 and 9 months post-transplantation, while in subcutaneous transplants, spermatogenic arrest was observed at 4 months and none of the transplants survived at 9 months.

WHAT IS KNOWN ALREADY

Auto-transplantation of cryopreserved immature testis tissue (ITT) could be a potential fertility restoration strategy for patients with complete loss of germ cells due to chemo- and/or radiotherapy at a young age. Before ITT transplantation can be used for clinical application, it is a prerequisite to demonstrate the feasibility of the technique and identify the conditions required for establishing spermatogenesis in primate ITT transplants. Although xenotransplantation of ITT from several species has resulted in complete spermatogenesis, in human and marmoset, ITT has not been successful.

STUDY DESIGN, SIZE, DURATION

In this study, we used marmoset as a pre-clinical animal model. ITT was obtained from two 6-month-old co-twin marmosets. A total of 147 testis tissue pieces (~0.8-1.0 mm3 each) were transplanted into the testicular parenchyma (intratesticular; n = 40) or under the dorsal skin (ectopic; n = 107) of 4-week-old immunodeficient Swiss Nu/Nu mice (n = 20). Each mouse received one single marmoset testis tissue piece in each testis and 4-6 pieces subcutaneously. Xenotransplants were retrieved at 4 and 9 months post-transplantation and evaluations were performed with regards to transplant survival, spermatogonial quantity and germ cell differentiation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Transplant survival was histologically evaluated by haematoxylin-periodic acid Schiff (H/PAS) staining. Spermatogonia were identified by MAGE-A4 via immunohistochemistry. Germ cell differentiation was assessed by morphological identification of different germ cell types on H/PAS stained sections. Meiotically active germ cells were identified by BOLL expression. CREM immunohistochemistry was performed to confirm the presence of post-meiotic germ cells and ACROSIN was used to determine the presence of round, elongating and elongated spermatids.

MAIN RESULTS AND THE ROLE OF CHANCE

Four months post-transplantation, 50% of the intratesticular transplants and 21% of the ectopic transplants were recovered (P = 0.019). The number of spermatogonia per tubule did not show any variation. In 33% of the recovered intratesticular transplants, complete spermatogenesis was established. Overall, 78% of the intratesticular transplants showed post-meiotic differentiation (round spermatids, elongating/elongated spermatids and spermatozoa). However, during the same period, spermatocytes (early meiotic germ cells) were the most advanced germ cell type present in the ectopic transplants. Nine months post-transplantation, 50% of the intratesticular transplants survived, whilst none of the ectopic transplants was recovered (P < 0.0001). Transplants contained more spermatogonia per tubule (P = 0.018) than at 4 months. Complete spermatogenesis was observed in all recovered transplants (100%), indicating a progressive spermatogenic development in intratesticular transplants between the two time-points. Nine months post-transplantation, transplants contained more seminiferous tubules with post-meiotic germ cells (37 vs. 5%; P < 0.001) and fewer tubules without germ cells (2 vs. 8%; P = 0.014) compared to 4 months post-transplantation.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although xenotransplantation of marmoset ITT was successful, it does not fully reflect all aspects of a future clinical setting. Furthermore, due to ethical restrictions, we were not able to prove the functionality of the spermatozoa produced in the marmoset transplants.

WIDER IMPLICATIONS OF THE FINDINGS

In this pre-clinical study, we demonstrated that testicular parenchyma provides the required microenvironment for germ cell differentiation and long-term survival of immature marmoset testis tissue, likely due to the favourable temperature regulation, growth factors and hormonal support. These results encourage the design of new experiments on human ITT xenotransplantation and show that intratesticular transplantation is likely to be superior to ectopic transplantation for fertility restoration following gonadotoxic treatment in childhood.

STUDY FUNDING/COMPETING INTEREST(S)

This project was funded by the ITN Marie Curie Programme 'Growsperm' (EU-FP7-PEOPLE-2013-ITN 603568) and the scientific Fund Willy Gepts from the UZ Brussel (ADSI677). D.V.S. is a post-doctoral fellow of the Fonds Wetenschappelijk Onderzoek (FWO; 12M2815N). No conflict of interest is declared.

Does the FSHB c.-211G>T polymorphism impact Sertoli cell number and the spermatogenic potential in infertile patients?

BACKGROUND

A genetic variant within the FSHB gene can deviate FSH action on spermatogenesis. The c.-211G>T FSHB single nucleotide polymorphism impacts FSHB transcription and biosynthesis due to interference with the LHX3 transcription factor binding. This SNP was previously shown to be strongly associated with lowered testicular volume, reduced sperm counts, and decreased FSH levels in patients carrying one or two T-alleles.

OBJECTIVE

To determine the impact of the SNP FSHB c.-211G>T on Sertoli cell (SC) number, Sertoli cell workload (SCWL) and thereby spermatogenic potential.

MATERIAL AND METHODS

Testicular biopsies of 31 azoospermic, homozygous T patients (26 non-obstructive azoospermia (NOA), and five obstructive azoospermia (OA)) were matched to patients with GG genotype. Marker proteins for SC (SOX9), spermatogonia (MAGE A4), and round spermatids (CREM) were used for semi-automatical quantification by immunofluorescence. SCWL (number of germ cells served by one SC) was determined and an unbiased clustering on the patient groups performed.

RESULTS

Quantification of SC number in NOA patients did not yield significant differences when stratified by FSHB genotype. SC numbers are also not significantly different between FSHB genotypes for the OA patient group and between NOA and OA groups. SCWL in the NOA patient cohort is significantly reduced when compared to the OA control patients; however, in neither group an effect of the genotype could be observed. The cluster analysis of the whole study cohort yielded two groups only, namely NOA and OA, and no clustering according to the FSHB genotype.

DISCUSSION AND CONCLUSION

The FSHB c.-211G>T polymorphism does not affect SC numbers or SCWL, thereby in principle maintaining the spermatogenic potential. The previously observed clinical phenotype for the FSHB genotype might therefore be caused by a hypo-stimulated spermatogenesis and not due to a decreased SC number.

Ageing in men with normal spermatogenesis alters spermatogonial dynamics and nuclear morphology in Sertoli cells

BACKGROUND

Ageing in men is believed to be associated with fertility decline and elevated risk of congenital disorders for the offspring. The previous studies also reported reduced germ and Sertoli cell numbers in older men. However, it is not clear whether ageing in men with normal spermatogenesis affects the testis and germ cell population dynamics in a way sufficient for transmitting adverse age effects to the offspring.

OBJECTIVES

We examined men with normal spermatogenesis at different ages concerning effects on persisting testicular cell types, that is the germ line and Sertoli cells, as these cell populations are prone to be exposed to age effects.

MATERIAL AND METHODS

Ageing was assessed in testicular biopsies of 32 patients assigned to three age groups: (i) 28.8 ± 2.7 years; (ii) 48.1 ± 1 years; and (iii) 70.9 ± 6.2 years, n = 8 each, with normal spermatogenesis according to the Bergmann-Kliesch score, and in a group of meiotic arrest patients (29.9 ± 3.8 years, n = 8) to decipher potential links between different germ cell types. Besides morphometry of seminiferous tubules and Sertoli cell nuclei, we investigated spermatogenic output/efficiency, and dynamics of spermatogonial populations via immunohistochemistry for MAGE A4, PCNA, CREM and quantified A-pale/A-dark spermatogonia.

RESULTS

We found a constant spermatogenic output (CREM-positive round spermatids) in all age groups studied. In men beyond their mid-40s (group 2), we detected increased nuclear and nucleolar size in Sertoli cells, indirectly indicating an elevated protein turnover. From the 7th decade (group 3) of life onwards, testes showed increased proliferation of undifferentiated spermatogonia, decreased spermatogenic efficiency and elevated numbers of proliferating A-dark spermatogonia.

DISCUSSION AND CONCLUSION

Maintaining normal sperm output seems to be an intrinsic determinant of spermatogenesis. Ageing appears to affect this output and might provoke compensatory proliferation increase in A spermatogonia which, in turn, might hamper germ cell integrity.

Microarray meta-analysis identifies candidate genes for human spermatogenic arrest

Male infertility affects approximately half of couples who have difficulty becoming pregnant, and its prevalence is continuously rising. Many studies have been performed using animal testes to reveal the mechanisms of male infertility, but few studies have investigated human testes due to various limitations. The aim of this study was to investigate the gene expression profile of impaired human testes through a meta-analysis of microarray data sets, which was accomplished by using 178 human testis samples and 7 microarray data sets. Impaired testes were categorised into four pathological phenotypes or the normal phenotype based on their Johnsen score. Then, a meta-analysis was performed to screen out the differentially expressed genes (DEGs) in each phenotype. The DEGs were used in a subsequent bioinformatics analysis. Our results identified several novel hub genes and pathways and suggested that G1 mitotic cell cycle arrest was a remarkable feature in pre-meiotic arrest. Furthermore, fifteen p53-interacting proteins, such as ABL1 and HDAC2, whose roles in spermatogenesis have not been well characterised, were selected from the DEGs through a strict screening procedure.

Spermatogonial behavior in marmoset: a new generation, their kinetics and niche

STUDY QUESTION

Could a more detailed evaluation of marmoset spermatogonial morphology, kinetics and niches using high-resolution light microscopy (HRLM) lead to new findings?

SUMMARY ANSWER

Three subtypes of marmoset undifferentiated spermatogonia, which were not evenly distributed in terms of number and position along the basal membrane, and an extra premeiotic cell division not present in humans were identified using HRLM.

WHAT IS KNOWN ALREADY

The seminiferous epithelium cycle (SEC) of marmosets is divided into nine stages when based on the acrosome system, and several spermatogenic stages can usually be recognized within the same tubular cross-section. Three spermatogonial generations have been previously described in marmosets: types Adark, Apale and B spermatogonia.

STUDY DESIGN, SIZE, DURATION

Testes from five adult Callithrix penicillata were fixed by glutaraldehyde perfusion via the cardiac route and embedded in Araldite plastic resin for HRLM evaluation. Semi-thin sections (1 μm) were analyzed morphologically and morphometrically to evaluate spermatogonial morphology and kinetics (number, mitosis and apoptosis), spermatogenesis efficiency and the spermatogonial niche.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Shape and nuclear diameter, the presence and distribution of heterochromatin, the granularity of the euchromatin, as well as the number, morphology and degree of nucleolar compaction were observed for morphological characterization. Kinetics analyses were performed for all spermatogonial subtypes and preleptotene spermatocytes, and their mitosis and apoptosis indexes determined across all SEC stages. Spermatogenesis parameters (mitotic, meiotic, Sertoli cell workload and general spermatogenesis efficiency) were determined through the counting of Adark and Apale spermatogonia, preleptotene and pachytene primary spermatocytes, round spermatids, and Sertoli cells at stage IV of the SEC.

MAIN RESULTS AND THE ROLE OF CHANCE

This is the first time that a study in marmosets demonstrates: the existence of a new spermatogonial generation (B2); the presence of two subtypes of Adark spermatogonia with (AdVac) and without (AdNoVac) nuclear rarefaction zones; the peculiar behavior of AdVac spermatogonia across the stages of the SEC, suggesting that they are quiescent stem spermatogonia; and that AdVac spermatogonia are located close to areas in which blood vessels, Leydig cells and macrophages are concentrated, suggesting a niche area for these cells.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

The C. penicillata spermatogonial kinetics evaluated here consider spermatogonial number across the SEC and their mitotic and apoptotic figures identified in HRLM sections. Therefore, caution is required when comparing absolute values between species. Although morphometric evaluation has suggested that AdVac spermatogonia are stem cells, a functional proof of this is still missing. It is known that parameters of the spermatogenic process in C. penicillata have similarities with those of the common marmoset C. jacchus, however, a detailed study of spermatogonial morphology, kinetics and niche has not yet been performed in C. jacchus, and a full comparison of the two species is not possible.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings in C. penicillata contribute to a better understanding of the spermatogonial behavior and spermatogenesis efficiency in non-human primates. Given the phylogenetic closeness of the marmoset to the human species, similar processes might occur in humans. Therefore, marmosets may be an excellent model for studies regarding human testicular biology, fertility and related disorders.

STUDY FUNDING/COMPETING INTEREST(S)

Experiments were partially supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) and Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq). The authors declare that there are no conflicts of interest.

Toxicologic Pathology Forum*: Opinion on Sexual Maturity and Fertility Assessment in Long-tailed Macaques ( Macaca fascicularis) in Nonclinical Safety Studies

If nonhuman primates represent the only relevant species for nonclinical safety evaluation of biotechnology-derived products, male and female fertility effects can be assessed in repeat dose toxicity studies given that sexually mature monkeys are used. This opinion piece provides recommendations for determining sexual maturity and when/how fertility assessments should be conducted in the cynomolgus monkey. Male sexual maturity should be proven by presence of sperm in a semen sample, female sexual maturity by at least two consecutive menstrual bleedings. As per regulatory guidance, default parameters for an indirect assessment of fertility in both sexes are reproductive organ weight and histopathology. Beyond default parameters, daily vaginal swabs are recommended for females, and for males, it is recommended to include blood collections (for potential analysis of reproductive hormones), testis volume sonography, and collection of frozen testis samples at necropsy. Only if there is a cause for concern, blood collection for potential reproductive hormone analysis should be conducted in females and semen analysis in males. In principle, adverse reproductive effects can be detected within 4 weeks of test article administration, depending on study design and reproductive end point chosen. Therefore, there are options for addressing reproductive toxicity aspects with studies of less than 3 months dosing duration. *This is an opinion article submitted to the Toxicologic Pathology Forum. It represents the views of the authors. It does not constitute an official position of the Society of Toxicologic Pathology, British Society of Toxicological Pathology, or European Society of Toxicologic Pathology, and the views expressed might not reflect the best practices recommended by these Societies. This article should not be construed to represent the policies, positions, or opinions of their respective organizations, employers, or regulatory agencies.

A comparison between the semen and sperm parameters from the captive-bred Vervet monkey (Chlorocebus aethiops) and Rhesus monkey (Macaca mulatta)

BACKGROUND

It is generally accepted that non-human primates (NHP) represent the model of choice for integrative studies of testicular function and endocrine control. However, there are many species-specific differences that necessitate identification prior to the selection of an appropriate model for these studies. In an NHP breeding facility, this opportunity of selection is usually presented during breeding periods when it is crucial to determine which individuals should be maintained as breeders. With reference to adult males and their use in breeding programs and reproductive studies, it is therefore imperative to document the normal semen and sperm values, expected seasonal changes and the variabilities found within samples and among individuals. The comparison of closely related species that differ by breeding seasonality will, therefore, highlight their value in reproductive research.

METHODS

Semen samples were obtained by rectal probe electroejaculation (RPE). The seminal and sperm characteristics of captive-bred Vervet monkeys (Chlorocebus aethiops) (n = 10) and Rhesus monkeys (Macaca mulatta) (n = 10) were evaluated and compared. Parameters such as semen volume, pH, sperm concentration, and sperm motility were analyzed by means of a computer-aided sperm analysis (CASA) system.

RESULTS

Large variations in semen and sperm parameter values indicated differences between species and samples. Monthly variations were observed for the Vervet regardless of breeding and conceptions that occurred throughout the year. In contrast, Rhesus seminal characteristics indicated a clear seasonal trend.

CONCLUSION

Non-human primates have long provided as research models for studying complexities of human reproductive biology. The baseline values reported from this study can be applied as guidelines during the selection of male individuals for reproductive studies. Of further interest is the comparative data on semen and sperm parameters between two congeneric species that differ by seasonal versus aseasonal breeding.

Comparative Aspects of Pre- and Postnatal Development of the Male Reproductive System

This review describes pre- and postnatal development of the male reproductive system in humans and laboratory animals, and highlights species differences in the timing and control of hormonal and morphologic events. Major differences are that the fetal testis is dependent on gonadotropins in humans, but is independent of such in rats; humans have an extended postnatal quiescent period, whereas rats exhibit no quiescence; and events such as secretion by the prostate and seminal vesicles, testicular descent, and the appearance of spermatogonia are all prenatal events in humans, but are postnatal events in rats. Major differences in the timing of the developmental sequence between rats and humans include: gonocyte transformation period (rat: postnatal day 0-9; human: includes gestational week 22 to 9 months of age); masculinization programming window (rat: gestational day 15.5-17.5; human: gestational week 9-14); and mini-puberty (rat: 0-6 hr after birth; human: 3-6 months of age). Endocrine disruptors can cause unique lesions in the prenatal and early postnatal testis; therefore, it is important to consider the differences in the timing of the developmental sequence when designing preclinical studies as identification of windows of sensitivity for endocrine disruption or toxicants will aid in interpretation of results and provide clues to a mode of action. Birth Defects Research 110:190-227, 2018. © 2017 Wiley Periodicals, Inc.

Mutation rates and the evolution of germline structure

Genome sequencing studies of de novo mutations in humans have revealed surprising incongruities in our understanding of human germline mutation. In particular, the mutation rate observed in modern humans is substantially lower than that estimated from calibration against the fossil record, and the paternal age effect in mutations transmitted to offspring is much weaker than expected from our long-standing model of spermatogenesis. I consider possible explanations for these discrepancies, including evolutionary changes in life-history parameters such as generation time and the age of puberty, a possible contribution from undetected post-zygotic mutations early in embryo development, and changes in cellular mutation processes at different stages of the germline. I suggest a revised model of stem-cell state transitions during spermatogenesis, in which 'dark' gonial stem cells play a more active role than hitherto envisaged, with a long cycle time undetected in experimental observations. More generally, I argue that the mutation rate and its evolution depend intimately on the structure of the germline in humans and other primates.This article is part of the themed issue 'Dating species divergences using rocks and clocks'.

Spermatogenesis: The Commitment to Meiosis

Mammalian spermatogenesis requires a stem cell pool, a period of amplification of cell numbers, the completion of reduction division to haploid cells (meiosis), and the morphological transformation of the haploid cells into spermatozoa (spermiogenesis). The net result of these processes is the production of massive numbers of spermatozoa over the reproductive lifetime of the animal. One study that utilized homogenization-resistant spermatids as the standard determined that human daily sperm production (dsp) was at 45 million per day per testis (60). For each human that means ∼1,000 sperm are produced per second. A key to this level of gamete production is the organization and architecture of the mammalian testes that results in continuous sperm production. The seemingly complex repetitious relationship of cells termed the "cycle of the seminiferous epithelium" is driven by the continuous commitment of undifferentiated spermatogonia to meiosis and the period of time required to form spermatozoa. This commitment termed the A to A1 transition requires the action of retinoic acid (RA) on the undifferentiated spermatogonia or prospermatogonia. In stages VII to IX of the cycle of the seminiferous epithelium, Sertoli cells and germ cells are influenced by pulses of RA. These pulses of RA move along the seminiferous tubules coincident with the spermatogenic wave, presumably undergoing constant synthesis and degradation. The RA pulse then serves as a trigger to commit undifferentiated progenitor cells to the rigidly timed pathway into meiosis and spermatid differentiation.

Application of three-dimensional culture systems to study mammalian spermatogenesis, with an emphasis on the rhesus monkey (Macaca mulatta)

In vitro culture of spermatogonial stem cells (SSCs) has generally been performed using two-dimensional (2D) culture systems; however, such cultures have not led to the development of complete spermatogenesis. It seems that 2D systems do not replicate optimal conditions of the seminiferous tubules (including those generated by the SSC niche) and necessary for spermatogenesis. Recently, one of our laboratories has been able to induce proliferation and differentiation of mouse testicular germ cells to meiotic and postmeiotic stages including generation of sperm in a 3D soft agar culture system (SACS) and a 3D methylcellulose culture system (MCS). It was suggested that SACS and MCS form a special 3D microenvironment that mimics germ cell niche formation in the seminiferous tubules, and thus permits mouse spermatogenesis in vitro. In this review, we (1) provide a brief overview of the differences in spermatogenesis in rodents and primates, (2) summarize data related to attempts to generate sperm in vitro, (3) report for the first time formation of colonies/clusters of cells and differentiation of meiotic (expression of CREM-1) and postmeiotic (expression of acrosin) germ cells from undifferentiated spermatogonia isolated from the testis of prepubertal rhesus monkeys and cultured in SACS and MCS, and (4) indicate research needed to optimize 3D systems for in vitro primate spermatogenesis and for possible future application to man.

Beyond Testis Size: Links between Spermatogenesis and Sperm Traits in a Seasonal Breeding Mammal

Spermatogenesis is a costly process that is expected to be under selection to maximise sperm quantity and quality. Testis size is often regarded as a proxy measure of sperm investment, implicitly overlooking the quantitative assessment of spermatogenesis. An enhanced understanding of testicular function, beyond testis size, may reveal further sexual traits involved in sperm quantity and quality. Here, we first estimated the inter-male variation in testicular function and sperm traits in red deer across the breeding and non-breeding seasons. Then, we analysed the relationships between the testis mass, eight parameters of spermatogenic function, and seven parameters of sperm quality. Our findings revealed that the Sertoli cell number and function parameters vary greatly between red deer males, and that spermatogenic activity co-varies with testis mass and sperm quality across the breeding and non-breeding seasons. For the first time in a seasonal breeder, we found that not only is the Sertoli cell number important in determining testis mass (r = 0.619, p = 0.007 and r = 0.248, p = 0.047 for the Sertoli cell number assessed by histology and cytology, respectively), but also sperm function (r = 0.703, p = 0.002 and r = 0.328, p = 0.012 for the Sertoli cell number assessed by histology and cytology, respectively). Testicular histology also revealed that a high Sertoli cell number per tubular cross-section is associated with high sperm production (r = 0.600, p = 0.009). Sperm production and function were also positively correlated (r = 0.384, p = 0.004), suggesting that these traits co-vary to maximise sperm fertilisation ability in red deer. In conclusion, our findings contribute to the understanding of the dynamics of spermatogenesis, and reveal new insights into the role of testicular function and the Sertoli cell number on testis size and sperm quality in red deer.

Sperm competition and the evolution of spermatogenesis

Spermatogenesis is a long and complex process that, despite the shared overall goal of producing the male gamete, displays striking amounts of interspecific diversity. In this review, we argue that sperm competition has been an important selection pressure acting on multiple aspects of spermatogenesis, causing variation in the number and morphology of sperm produced, and in the molecular and cellular processes by which this happens. We begin by reviewing the basic biology of spermatogenesis in some of the main animal model systems to illustrate this diversity, and then ask to what extent this variation arises from the evolutionary forces acting on spermatogenesis, most notably sperm competition. We explore five specific aspects of spermatogenesis from an evolutionary perspective, namely: (i) interspecific diversity in the number and morphology of sperm produced; (ii) the testicular organizations and stem cell systems used to produce them; (iii) the large number and high evolutionary rate of genes underpinning spermatogenesis; (iv) the repression of transcription during spermiogenesis and its link to the potential for haploid selection; and (v) the phenomenon of selection acting at the level of the germline. Overall we conclude that adopting an evolutionary perspective can shed light on many otherwise opaque features of spermatogenesis, and help to explain the diversity of ways in which males of different species perform this fundamentally important process.

Separation of somatic and germ cells is required to establish primate spermatogonial cultures

STUDY QUESTION

Can primate spermatogonial cultures be optimized by application of separation steps and well defined culture conditions?

SUMMARY ANSWER

We identified the cell fraction which provides the best source for primate spermatogonia when prolonged culture is desired.

WHAT IS KNOWN ALREADY

Man and marmoset show similar characteristics in regard to germ cell development and function. Several protocols for isolation and culture of human testis-derived germline stem cells have been described. Subsequent analysis revealed doubts on the germline origin of these cells and characterized them as mesenchymal stem cells or fibroblasts. Studies using marmosets as preclinical model confirmed that the published isolation protocols did not lead to propagation of germline cells.

STUDY DESIGN, SIZE, DURATION

Testicular cells derived from nine adult marmoset monkeys (Callithrix jacchus) were cultured for 1, 3, 6 and 11 days and consecutively analyzed for the presence of spermatogonia, differentiating germ cells and testicular somatic cells.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Testicular tissue of nine adult marmoset monkeys was enzymatically dissociated and subjected to two different cell culture approaches. In the first approach all cells were kept in the same dish (non-separate culture, n = 5). In the second approach the supernatant cells were transferred into a new dish 24 h after seeding and subsequently supernatant and attached cells were cultured separately (separate culture, n = 4). Real-time quantitative PCR and immunofluorescence were used to analyze the expression of reliable germ cell and somatic markers throughout the culture period. Germ cell transplantation assays and subsequent wholemount analyses were performed to functionally evaluate the colonization of spermatogonial cells.

MAIN RESULTS AND THE ROLE OF CHANCE

This is the first report revealing an efficient isolation and culture of putative marmoset spermatogonial stem cells with colonization ability. Our results indicate that a separation of spermatogonia from testicular somatic cells is a crucial step during cell preparation. We identified the overgrowth of more rapidly expanding somatic cells to be a major problem when establishing spermatogonial cultures. Initiating germ cell cultures from the supernatant and maintaining germ cells in suspension cultures minimized the somatic cell contamination and provided enriched germ cell fractions which displayed after 11 days of culture a significantly higher expression of germ cell markers genes (DDX-4, MAGE A-4; P < 0.05) compared with separately cultured attached cells. Additionally, germ cell transplantation experiments demonstrated a significantly higher absolute number of cells with colonization ability (P < 0.001) in supernatant cells after 11 days of separate culture.

LIMITATIONS, REASONS FOR CAUTION

This study presents a relevant aspect for the successful setup of spermatogonial cultures but provides limited data regarding the question of whether the long-term maintenance of spermatogonia can be achieved. Transfer of these preclinical data to man may require modifications of the protocol.

WIDER IMPLICATIONS OF THE FINDINGS

Spermatogonial cultures from rodents have become important and innovative tools for basic and applied research in reproductive biology and veterinary medicine. It is expected that spermatogonia-based strategies will be transformed into clinical applications for the treatment of male infertility. Our data in the marmoset monkey may be highly relevant to establish spermatogonial cultures of human testes.

STUDY FUNDING/COMPETING INTERESTS

Funding was provided by the DFG-Research Unit FOR 1041 Germ Cell Potential (SCHL394/11-2) and by the Graduate Program Cell Dynamics and Disease (CEDAD) together with the International Max Planck Research School - Molecular Biomedicine (IMPRS-MBM). The authors declare that there is no conflict of interest.

TRIAL REGISTRATION NUMBER

Not applicable.

Spermatogonial SOHLH1 nucleocytoplasmic shuttling associates with initiation of spermatogenesis in the rhesus monkey (Macaca mulatta)

As the spermatogenesis- and oogenesis-specific basic helix-loop-helix 1 (SOHLH1) transcription factor has been shown to be essential for spermatogonial differentiation in mice, we examined the immunoexpression of this protein in the testis of the rhesus monkey (Macaca mulatta) during puberty, the stage of development when spermatogonial differentiation is initiated in higher primates. Immunopositive SOHLH1 cells were observed only on the basement membrane of the seminiferous cords and tubules. Prior to puberty, essentially 100% of SOHLH1-positive spermatogonia co-expressed the glial cell line-derived neurotrophic factor family receptor alpha 1 (GFRα1), a marker for undifferentiated spermatogonia, and >80% of the immunopositive SOHLH1 cells exhibited only cytoplasmic staining of this transcription factor. Nuclear-only SOHLH1 was found in <10% of spermatogonia in testes from pre-pubertal animals. Puberty was associated with a dramatic and progressive increase in the percentage of immunopositive SOHLH1 cells with nuclear-only staining, and this was associated with (i) a marked reduction in the fraction (∼100-20%) of SOHLH1-positive germ cells co-expressing GFRα1 and (ii) a significant increase in the proportion of SOHLH1-positive spermatogonia that co-expressed the tyrosine kinase receptor (cKIT). Spermatogonia exhibiting nuclear SOHLH1 staining were found to be cKIT positive, but not all cKIT-positive spermatogonia exhibited nuclear SOHLH1 staining. Taken together, these results suggest that, in the monkey, nuclear location of SOHLH1 is closely associated with spermatogonial differentiation.

Gonadal expression of Foxo1, but not Foxo3, is conserved in diverse Mammalian species

The Foxos are key effectors of the PI3K/Akt signaling pathway and regulate diverse physiologic processes. Two of these factors, Foxo1 and Foxo3, serve specific roles in reproduction in the mouse. Foxo3 is required for suppression of primordial follicle activation in females, while Foxo1 regulates spermatogonial stem cell maintenance in males. In the mouse ovary, Foxo1 is highly expressed in somatic cells (but not in oocytes), suggesting an important functional role for Foxo1 in these cells. Given that invertebrate model species such as Caenorhabditis elegans and Drosophila melanogaster harbor a single ancestral Foxo homolog, these observations suggest that gene duplication conferred a selective advantage by permitting the Foxos to adopt distinct roles in oogenesis and spermatogenesis. Our objective was to determine if the remarkably specific expression patterns of Foxo1 and Foxo3 in mouse gonads (and, by inference, Foxo function) are conserved in diverse mammalian species. Western blotting was used to validate isoform-specific antibodies in rodents, companion animals, farm animals, nonhuman primates, and humans. Following validation of each antibody, immunohistochemistry was performed to ascertain Foxo1 and Foxo3 gonadal expression patterns. While Foxo1 expression in spermatogonia and granulosa cells was conserved in each species evaluated, Foxo3 expression in oocytes was not. Our findings suggest that Foxo3 is not uniquely required for primordial follicle maintenance in nonrodent species and that other Foxos, particularly Foxo1, may contribute to oocyte maintenance in a functionally redundant manner.

Experimental endocrine manipulation by contraceptive regimen in the male marmoset (Callithrix jacchus)

Marmosets are used as preclinical model in reproductive research. In contrast to other primates, they display short gestation times rendering this species valid for exploration of effects on fertility. However, their peculiar endocrine regulation differs from a those of macaques and humans. We subjected male marmosets to previously clinically tested hormonal regimens that are known to effectively suppress spermatogenesis. Beside a control group, seven groups (each n=6) were investigated for different periods of up to 42 months: regimen I, (four groups) received testosterone undecanoate (TU) and norethisterone enanthate (NETE); regimen II, (two groups) received TU and NETE followed by NETE only; and regimen III, (one group) received NETE only. Testicular volume, cell ploidy and histology, endocrine changes and fertility were monitored weekly. TU and NETE and initial TU and NETE treatment followed by NETE failed to suppress spermatogenesis and fertility. Testicular volumes dropped, although spermatogenesis was only mildly affected; however, testicular cellular composition remained stable. Serum testosterone dropped when NETE was given alone but the animals remained fertile. Compared with controls, no significant changes were observed in sperm motility and fertility. Administration of TU and NETE affected testicular function only mildly, indicating that the regulatory role of chorionic gonadotrophin and testosterone on spermatogenesis is obviously limited and testicular function is maintained, although the endocrine axis is affected by the treatment. In conclusion, marmosets showed a different response to regimens of male contraception from macaques or men and have to be considered as a problematic model for preclinical trials of male hormonal contraception.

Concise review: Spermatogenesis in an artificial three-dimensional system

Culture of spermatogonial stem cells has been performed under a variety of conditions. Most featured two-dimensional systems, with different types of sera, conditioned media, feeder layers, and growth factors. Some have used three-dimensional (3D) matrices produced from gelatin, collagen, or other material. In spite of their increasingly sophisticated composition, however, complete spermatogenesis in vitro has not yet been achieved. In the seminiferous tubules, spermatogenesis occurs in an environment where cells are embedded in a 3D structure with specific niches regulating each stage of germ cell maturation mediated by hormones and paracrine/autocrine factors. We have recently reported achievement of complete in vitro spermatogenesis of mouse testicular germ cells in a 3D culture system featuring a soft agar matrix. This review discusses the advantages of the 3D culture system for studying the spermatogenic process in its entirety. Also discussed are the steps necessary to expand the applicability of the 3D culture system to human germ cell development and determine the functionality of culture-produced spermatozoa for generating offspring.

Male and female fertility assessment in the cynomolgus monkey following administration of ABT-874, a human Anti-IL-12/23p40 monoclonal antibody

BACKGROUND

ABT-874 is an anti-IL-12/23 monoclonal antibody that binds to the p40 subunit of human IL-12 and IL-23. As part of its preclinical safety assessment, studies were conducted to asses its potential effects on the reproductive system in male and female cynomolgus monkeys.

METHODS

Sexually mature male cynomolgus monkeys (n = 6/group) were administered once weekly subcutaneous doses of 0, 5, 25, or 100 mg/kg ABT-874 for 13 weeks. Four monkeys/group were necropsied at the end of the 13-week dosing period and two monkeys/group were necropsied following an 8-week recovery period. Endpoints assessed in these males included sperm parameters such as sperm count and morphology, male reproductive hormones, and testes histopathology. Sexually mature female cynomolgus monkeys (n = 6/group) were administered subcutaneous doses of 0, 5, 25, or 100 mg/kg/week ABT-874 for two menstrual cycles, and recovery was subsequently assessed in each of these animals over two menstrual cycles. Endpoints assessed in these females included menses and reproductive hormone levels.

RESULTS

In both the male and female fertility studies, there were no unscheduled deaths and there was no evidence of toxicity. In male monkeys, there were no ABT-874-related effects on sperm count or motility, histopathology of the testes or effects on testosterone and inhibin B levels. In addition, menstrual cycle length, progesterone, 17ß-estradiol, and luteinizing hormone levels in female monkeys were comparable among control and ABT-874-treated groups.

CONCLUSIONS

These results demonstrate that ABT-874 had no adverse effects on reproductive hormones or fertility parameters in male or female cynomolgus monkeys.

Postnatal testicular development in mouse species with different levels of sperm competition

Postcopulatory sexual selection leads to an increase in sperm numbers which is partly the result of an increase in relative testes mass and could also be the consequence of changes in testis architecture or function. Very little is known regarding developmental changes during the first spermatogenic wave that may lead to enhanced spermatogenic efficiency and increased sperm production. We examined testicular development after birth in four mouse species with different sperm competition levels to assess changes in testicular architecture and function. Differences in relative testes mass between species appeared soon after birth and were exacerbated thereafter. The volume of testes occupied by seminiferous tubules differed between species postnatally and were associated with sperm competition levels. Finally, changes over time in the proportions of tubules with different germ cell types were also associated with sperm competition levels, with the time taken for the transition between various cell stages being negatively associated with levels of sperm competition. We conclude that postnatal testis development differs between closely related species with different sperm competition levels influencing testis architecture and the rate of progression of spermatogenesis, leading to differences in testis function at reproductive maturity.

Sperm competition leads to functional adaptations in avian testes to maximize sperm quantity and quality

The outcome of sperm competition (i.e. competition for fertilization between ejaculates from different males) is primarily determined by the relative number and quality of rival sperm. Therefore, the testes are under strong selection to maximize both sperm number and quality, which are likely to result in trade-offs in the process of spermatogenesis (e.g. between the rate of spermatogenesis and sperm length or sperm energetics). Comparative studies have shown positive associations between the level of sperm competition and both relative testis size and the proportion of seminiferous (sperm-producing) tissue within the testes. However, it is unknown how the seminiferous tissue itself or the process of spermatogenesis might evolve in response to sperm competition. Therefore, we quantified the different germ cell types and Sertoli cells (SC) in testes to assess the efficiency of sperm production and its associations with sperm length and mating system across 10 species of New World Blackbirds (Icteridae) that show marked variation in sperm length and sperm competition level. We found that species under strong sperm competition generate more round spermatids (RS)/spermatogonium and have SC that support a greater number of germ cells, both of which are likely to increase the maximum sperm output. However, fewer of the RS appeared to elongate to mature spermatozoa in these species, which might be the result of selection for discarding spermatids with undesirable characteristics as they develop. Our results suggest that, in addition to overall size and gross morphology, testes have also evolved functional adaptations to maximize sperm quantity and quality.

Overview of the marmoset as a model in nonclinical development of pharmaceutical products

Callithrix jacchus (common marmoset) is one of the more primitive non-human primate species and is used widely in fundamental biology, pharmacology and toxicology studies. Marmosets breed well in captivity with good reproductive efficiencies and their sexual maturity is reached within 18 months of age allowing for rapid expansion of colonies and early availability of sexually mature animals permitting an earlier assessment of product candidates in the adult. Their relatively small size allows a reduction in material requirements leading to a reduction in development time and cost. Fewer animals are also required due to their ability to be used in both pharmacology and toxicology (nonclinical) studies. These factors, alongside a better understanding of their optimal nutrient and welfare requirements over recent years, facilitate the generation of a more cohesive and robust dataset. With the growth of biotechnology-derived pharmaceuticals, non-human primate use has, by necessity, also increased; nevertheless, there is also a growing public call for minimizing their use. Utilizing, the more primitive marmoset species may provide the optimal compromise and once the scientific rationale has been carefully considered and their use justified, there are several advantages to using the marmoset as a model in nonclinical development of pharmaceutical products.

Germ cell dynamics in the testis of the postnatal common marmoset monkey (Callithrix jacchus)

The seminiferous epithelium in the nonhuman primate Callithrix jacchus is similarly organized to man. This monkey has therefore been used as a preclinical model for spermatogenesis and testicular stem cell physiology. However, little is known about the developmental dynamics of germ cells in the postnatal primate testis. In this study, we analyzed testes of newborn, 8-week-old, and adult marmosets employing immunohistochemistry using pluripotent stem cell and germ cell markers DDX4 (VASA), POU5F1 (OCT3/4), and TFAP2C (AP-2γ). Stereological and morphometric techniques were applied for quantitative analysis of germ cell populations and testicular histological changes. Quantitative RT-PCR (qRT-PCR) of testicular mRNA was applied using 16 marker genes establishing the corresponding profiles during postnatal testicular development. Testis size increased during the first 8 weeks of life with the main driver being longitudinal outgrowth of seminiferous cords. The number of DDX4-positive cells per testis doubled between birth and 8 weeks of age whereas TFAP2C- and POU5F1-positive cells remained unchanged. This increase in DDX4-expressing cells indicates dynamic growth of the differentiated A-spermatogonial population. The presence of cells expressing POU5F1 and TFAP2C after 8 weeks reveals the persistence of less differentiated germ cells. The mRNA and protein profiles determined by qRT-PCR and western blot in newborn, 8-week-old, and adult marmosets corroborated the immunohistochemical findings. In conclusion, we demonstrated the presence of distinct spermatogonial subpopulations in the primate testis exhibiting different dynamics during early testicular development. Our study demonstrates the suitability of the marmoset testis as a model for human testicular development.

Release of DEFB126 from macaque sperm and completion of capacitation are triggered by conditions that simulate periovulatory oviductal fluid

Capacitation of macaque sperm in vitro has been achieved efficiently only with the addition of both cyclic nucleotides and methylxanthines. The use of these exogenous sperm activators clouds an understanding of the normal mechanisms underlying capacitation and may slow early embryo development following in vitro fertilization (IVF). We demonstrate that culture medium which simulates periovulatory oviductal fluid with respect to bicarbonate (HCO(3)(-)) and glucose concentration induces capacitation in a high percentage of macaque sperm as determined by the ability of sperm to undergo both the release of coating protein DEFB126 and the zona pellucida-induced acrosome reaction (AR). Few sperm were able to undergo the AR following 6 hr incubation in medium containing either 35 mM HCO(3)(-) (approximately 7.2 pH) or 90 mM HCO(3)(-) (approximately pH 7.8) with 5 mM glucose. When glucose concentration was lowered to 0.5 mM to match levels reported for women at midcycle, the AR rate increased significantly in sperm incubated in both levels of HCO(3)(-), indicating that glucose interferes with sperm responsiveness to increasing HCO(3)(-) concentration observed in the primate oviduct during ovulation. Even greater synchronization of capacitation could be achieved with nonphysiologic extremes of alkalinity or energy substrate deprivation. In the latter case, sperm achieved high rates of IVF. A shift in pH from 7.2 to 7.8 in a HEPES-buffered medium was sufficient to remove DEFB126 from the surface of most sperm after only 3 hr. The loss of DEFB126 from sperm under periovulaory fluid conditions has implications for the timing of release of sperm from the oviductal reservoir.

Sperm competition selects beyond relative testes size in birds

Sperm morphology varies considerably across taxa, and postcopulatory sexual selection is thought to be one of the main forces responsible for this diversity. Several studies have investigated the effects of the variation in sperm design on sperm function, but the consequences of variation in sperm design on testis morphology have been overlooked. Testes size or architecture may determine the size of the sperm they produce, and selection for longer sperm may require concomitant adaptations in the testes. Relative testes size differs greatly between species and is often used as an index of sperm competition, but little is known about whether larger testes have more sperm-producing tissue or produce sperm at a faster rate. Using a comparative approach in New World Blackbirds (Icteridae), we found (1) a strong link between testis histology and sperm length, suggesting selection on testis architecture through selection on sperm size, and (2) that species under intense sperm competition had a greater proportion of sperm-producing tissue within their testes. These results support the prediction that sperm competition fosters adaptations in reproductive organs that extend beyond testes size, and raise questions about the trade-offs influencing reproductive investment.

The fate of paternal mitochondria in marmoset pre-implantation embryos

BACKGROUND

Sperm-derived mitochondria are integrated into the oocyte at fertilization but seem to vanish during the early cleavage phase. The developmental potential of pre-implantation embryos seems to be closely related to their ability to induce degeneration of these mitochondria, but the mechanisms underlying their loss of function are not yet understood. This study focuses on the fate of paternal mitochondria in pre-implantation embryos.

METHODS

Stimulation, collection and in vitro culture of oocytes from Callithrix jacchus, allows the study of the destiny of paternal mitochondria by utilizing immunostaining of pre-implantation embryos, fluorescence and laserscanning microscopy. Live pre-implantation embryos were stained with a fluorescence indicator reflecting mitochondrial membrane potential.

RESULTS

Evidence indicating the loss of mitochondrial function was not found nor that apoptosis pathways were involved in the disappearance of paternally derived mitochondria.

CONCLUSIONS

These findings may have implications for mitochondrially inherited diseases and could lead to new strategies for improving assisted reproduction.

Complete spermatogenesis in orthotopic but not in ectopic transplants of autologously grafted marmoset testicular tissue

Testicular grafting has the potential to become a method to preserve fertility in prepubertal boys undergoing cancer treatment. The possibility of successful germ cell maturation after autologous grafting should be proven preclinically in a nonhuman primate model. Therefore, in two experiments, we analyzed the potential of autologous testicular grafting in the marmoset model. A first experiment in immature and adult hemi-castrated monkeys addressed the question of whether full spermatogenesis in an ectopic graft could be achieved under a relatively normal endocrine milieu and whether the donor's age is of influence. A second experiment in castrated immature animals examined whether the transplantation site [ectopic (back skin) or orthotopic (scrotum)] influences spermatogenic progress and whether cryopreserved tissue can be successfully transplanted. Grafts were analyzed by histology, immunohistochemistry, and morphometry. Bioactive chorionic gonadotropin and serum testosterone were measured. In the adults, ectopic grafts degenerated, whereas in the immature animals, grafts survived at the spermatogonial level. In the castrates, none of the cryopreserved grafts survived, ectopic grafts were meiotically arrested, but orthotopic transplants completed spermatogenesis. Androgen and bioactive chorionic gonadotropin levels were not decisive for graft development. When ectopic and orthotopic transplantation sites were compared, the scrotum has a substantially lower temperature. Thus, the higher temperature at the ectopic transplantation site may contribute to spermatogenic arrest. Autologous grafting of nonhuman primate testicular tissues can result in complete spermatogenesis. Our findings indicate that transplantation site and developmental age of the tissue play a role more important than the endocrine milieu.

Age-related changes in diurnal rhythms and levels of gonadotropins, testosterone, and inhibin B in male rhesus monkeys (Macaca mulatta)

Testosterone shows circadian rhythms in monkeys with low serum levels in the morning hours. The decline relies on a diminished frequency of LH pulses. Inhibin B shows no diurnal patterns. In elderly men, the diurnal rhythm of testosterone is blunted and inhibin levels fall. Here we explore whether aging exerts similar effects in the rhesus monkey. We collected blood samples from groups of young (6-9 yr) and old (12-16 yr) male rhesus monkeys at 20-min intervals for a period of 24 h under remote sampling via a venous catheter. We determined moment-to-moment changes in plasma levels of testosterone, FSH, and LH by RIA, and of inhibin B by ELISA. We found significant diurnal patterns of testosterone in both groups. The circadian rhythm in testosterone was enhanced in older monkeys. Testosterone levels and pulse frequencies dropped significantly below those of young monkeys during midday hours. Diminished pulse frequency of LH appeared to be responsible for the midday testosterone decrease in old monkeys, while LH and testosterone pulse frequency did not change in young monkeys at corresponding time points. Old monkeys showed extended periods of LH-pulse quiescence in the morning and midday hours. Inhibin B and FSH levels were generally lower in old monkeys compared with the young group, but neither inhibin B nor FSH showed circadian rhythms. We conclude from these data that old rhesus monkeys have a more prominent circadian rhythm of LH and testosterone resulting from an extended midday period of quiescence in the hypothalamus-pituitary-gonadal axis.