Seasonal variations cause morphological changes and altered spermatogenesis in the testes of viscacha (Lagostomus maximus)

Photoperiod-regulated mitophagy in the germ cells of Brandt's voles (Lasiopodomys brandtii)

Photoperiod is a pivotal factor in affecting testicular function and spermatogenesis in seasonal-breeding animals. Mitophagy is essential for spermatogenesis, but its association with seasonal photoperiods has not been studied extensively. To explore this, we exposed male Brandt's voles (Lasiopodomys brandtii) to long-photoperiod (LP, 16 h/day) and short-photoperiod (SP, 8 h/day) conditions from their embryonic stages. Our results indicated that testis weight, volume, and relative testes weight were all significantly increased in LP compared to SP. Additionally, blood testosterone levels were markedly higher in LP than SP. Histological examination revealed that seminiferous diameter and epithelium thickness were greater in LP, with an increased abundance of germ cell types and cell numbers compared to SP. RT-qPCR analysis showed that mitophagy-promoting genes, such as Pink1, Prkn, Tomm7, Mnf2, Lc3, Optn, Gabarap, and Nbr1 were all upregulated in LP. Fluorescence in situ hybridization indicated that Pink1 expression was present in spermatogonia in SP, while in LP, Pink1 expression extended to almost all germ cell types with significantly higher mean optical density. Prkn expression was found in all germ cell types in both LP and SP, with a significantly higher mean optical density of 10-week-old LP males. Transmission electron microscopy showed normal mitochondrial morphology with clear membranes in SP, while the LP group had reduced cristae in mitochondria and damaged mitochondria undergoing autophagy. This study suggests that mitophagy may be involved in the photoperiodic spermatogenesis in Brandt's voles, providing insights into the role of photoperiod in seasonal reproduction in wild animals.

Seasonal change of circulating leptin associated with testicular activities of the wild ground squirrels (Citellus dauricus)

The purpose of this study was to explore the variations in the circulating leptin concentrations of the wild ground squirrels in relation to seasonal changes in testicular activities. Hematoxylin-eosin staining showed all types of elongated spermatids and spermatogenic cells existed in the testis in April, while the primary spermatocytes and spermatogonia were most advanced stages of germ cells in June. In addition, the primary spermatocytes, secondary spermatocytes, and spermatogonia were most advanced stages of germ cells in September. The highest circulating leptin concentration was consistent with the maximum body weight results from accumulation of adipose tissue in September. The mRNA expression level of leptin receptor (Ob-R) and STAT3 was lowest in June, raised in September, and remained increased in April. Ob-R and STAT3 were stronger staining in the Leydig cells in July. Moreover, the concentrations of testosterone (T) showed the maximum values in April, the minimum values in June, and significant increases in September. Furthermore, it is worth noting that the levels of T increased with the mRNA levels of Ob-R, STAT3, StAR, and testicular steroidogenic enzymes (3β-HSD, P450c17, and P450scc). Moreover, RNA-seq analyses of testis during the different periods showed that a total of 4209 genes were differentially expressed genes (DEGs); further analysis revealed that DEGs related with the Jak/STAT pathways and reproduction were altered. Taken together, the results suggested that the leptin regulated testicular function through the Jak/STAT pathways and testicular steroidogenic factor expressions.

Seasonal changes in the expression of molecular markers of stallion germ cells

The economic impacts of infertility and subfertility of stallions greatly influence the horse breeding industry. Self-renewal and differentiation of spermatogonial stem cells are the initial processes to maintain an adequate sperm population. Thus, understanding these processes may provide useful information to reveal the causes and remedies of subfertile and infertile stallions. Stallions are seasonal breeders. About 50% of the sperm population is reduced during the non-breeding season (NBS) in stallions. The seasonal regulation of spermatogenesis renders stallions as ideal models to understand the process of sperm production. Furthermore, comparing internal and external factors related to spermatogenesis during the breeding season (BS) and NBS may provide a solution for subfertile/infertile stallions. It is especially pertinent to study the expression pattern of different protein markers during undifferentiated, differentiating, and differentiated spermatogonia. Deleted in azoospermia-like (DAZL), undifferentiated cell transcription factor 1 (UTF-1), and protein gene product 9.5 (PGP9.5) are the molecular markers expressed at different stages of spermatogenesis. However, whether the expression pattern of these molecular markers is similar throughout the year in stallion remains undetermined. The objectives of this study were to (1) investigate the expression pattern and localization of DAZL, UTF-1, and PGP9.5 within seminiferous tubules and (2) evaluate the relative mRNA levels of these three germ cell markers in stallion testes during BS and NBS. Immunohistochemistry was performed to check and compare the expression pattern and localization of DAZL, UTF-1, and PGP9.5 antibodies. Reverse transcription-quantitative PCR analysis was performed to calculate the relative mRNA expression levels in the testes. Testicular tissues from thoroughbred stallions were collected during routine castration that was carried out in field conditions. Immunostaining of germ cells with DAZL and UTF-1 in BS and NBS were not significantly different. However, the relative mRNA expression levels of DAZL and UTF-1 were significantly different in both groups. Interestingly, the immunolabeling and the relative mRNA expression of PGP9.5 were significantly different between BS and NBS. From these results, it is hypothesized that the expression level of these putative molecular markers might be gonadotropin-dependent in stallion testes.

Seasonal reproduction and gonadal function: A focus on humans starting from animal studies

Photoperiod impacts reproduction in many species of mammals. Mating occurs at specific seasons to achieve reproductive advantages, such as optimization of offspring survival. Light is the main regulator of these changes during the photoperiod. Seasonally breeding mammals detect and transduce light signals through extraocular photoreceptor, regulating downstream melatonin-dependent peripheral circadian events. In rodents, hormonal reduction and gonadal atrophy occur quickly, and consensually with short-day periods. It remains unclear whether photoperiod influences human reproduction. Seasonal fluctuations of sex hormones have been described in humans, although they seem to not imply adaptative seasonal pattern in human gonads. This review discusses current knowledge about seasonal changes in the gonadal function of vertebrates, including humans. The photoperiod-dependent regulation of hypothalamic-pituitary-gonadal axis, as well as morphological and functional changes of the gonads are evaluated herein. Endocrine and morphological variations of reproductive functions, in response to photoperiod, are of interest as they may reflect the nature of past population selection for adaptative mechanisms that occurred during evolution.

Placentation and embryo death in the plains viscacha (Lagostomus maximus)

Caviomorpha are an exceptional group among rodents due to their extended gestational period and the delivery of precocial offspring. Among them, Lagostomus maximus is characterized by its polyovulation, polyembryony, and the highest embryonic death known in mammals. Its chorioallantoic placenta is hemomonochorial, an ancestral character among rodents. It resembles more the human placenta than the murine models. As in all caviomophs, the chorioallantoic placenta is divided in a main placenta and a subplacenta. The former is organized in labyrinth lobes surrounded by trophospongium, as in most caviomorphs. The giant cells (more numerous than in other caviomorphs) near the decidua could be related to invasiveness. During placentation of L. maximus, uterine natural killer cells are found. These cells have been related to invasiveness and remodeling of blood vessels in Mus musculus and Homo sapiens, although in other caviomorphs are not frequently found. In L. maximus, the placenta develops in all conceptuses (5-6 per uterine horn). Necrosis was observed in each implantation site at day 70 post-coitum, except in that closest to the vagina in each horn. This process of embryo death followed by resorption begins at day 26-30 post-coitum. Recently, we found variations in the percentage of blood vessel and uterine gland areas that could explain the regional differences in embryo survival. The characteristics of the placenta and implantation of L. maximus are important to stablish a unique model for studying placentation as well as early embryonic death, of interest for human and veterinary medicine.

Effects of photoperiod on morphology and function in testis and epididymis of Cricetulus barabensis

Photoperiod regulates the seasonal reproductive rhythms of mammals by influencing the development and function of sexual organs; however, the underlying mechanism remains unclear. We examined the morphology and functioning of the main sex organs of striped dwarf hamsters (Cricetulus barabensis) under different photoperiods (short daylight [SD], moderate daylight [MD], and long daylight [LD]) and further investigated the underlying molecular mechanisms. There was an inverse correlation between blood melatonin levels and photoperiod in the order SD > MD > LD. Decreases in body and tissue weights were observed under SD, whereas testis and epididymis weights between MD and LD were comparable. The diameters of the spermatogenic tubules, thickness of the spermatogenic epithelium, and the number of spermatogonia and Sertoli cells decreased under SD, whereas the serum-luteinizing hormone, follicle-stimulating hormone, and fecal testosterone concentrations decreased under LD. In SD, bax/bcl2 protein expression increased in the testes and decreased in the epididymides, whereas LC3II/LC3I remained unchanged in the testes and increased in the epididymides compared with the MD group. In LD, bax/bcl2 and LC3II/LC3I protein expression levels were unchanged in the testes but were decreased in the epididymides. In SD and LD, adenosine triphosphate synthase and citrate synthase protein expression levels were unchanged in the testes but were decreased in the epididymides. Drp1 and Mff protein expression increased in the testes and decreased in the epididymides. Overall, different regulatory mechanisms in the testis and epididymis led to degeneration under SD and maintenance under LD, preferentially protecting mitochondrial function in the testis by regulating mitochondrial fission.

Assessment of Testicular Lhcgr mRNA Expression Correlated with Testis and Seminal Vesicle Activities in the Libyan jird (Meriones libycus, Rodentia: Muridae) during Breeding Season Compared with Nonbreeding Season

Simple Summary

The breeding periods of desert rodents should be favorable to the survival of small young, conditioned by the availability of food that occurs in the Libyan jird biotope during the long photoperiod and the high temperatures. The Libyan jird (Meriones libycus) were caught in their natural biotope in the Saharan desert in Algeria and showed a seasonal cycle of the testis activity, characterized by the highest peak during spring (the breeding season) and the lowest activity was registered during autumn and winter (nonbreeding season). Lhcgr mRNA expression is increased in autumn and decreased in spring. This expression varied in an opposite manner to testicular and seminal vesicle structures.

Abstract

The Libyan jird (Meriones libycus, 1823) is a wild desert rodent that is a seasonal breeder species adapted to breed when the environmental conditions can satisfy the energy and hydrous requirements of pregnant and nursing females to ensure that births occur at the most favorable time of the year. We assessed gene expression of testicular luteinizing hormone receptor (Lhcgr) correlated to testis activity. The expression of Lhcgr was evaluated using quantitative Real Time-Polymerase Chain Reaction (qRT-PCR and the testis activity by a histological method in adult male Libyan jirds during the nonbreeding and breeding seasons. Our results showed that Lhcgr mRNA expression increased in autumn during the nonbreeding season and decreased in spring during the breeding season. This expression varied in contrast to testicular structure or function and plasma testosterone levels. These results help to elucidate this desert rodent’s seasonal sexual activity, which is correlated with central regulation.

Immunomorphometric variations of sustentacular cells of the male viscacha adrenal medulla during the annual reproductive cycle. Effects of androgens and melatonin

The adrenal medulla is crucial for the survival of species facing significant environmental changes. The parenchyma is composed mainly of chromaffin cells, ganglion cells and sustentacular cells (SC). The male viscacha exhibits seasonal variations of gonadal activity and other metabolic functions. The aim of this work was to investigate the influence of the reproductive conditions on the morphology of SC of this rodent. In addition, the effects of testosterone and melatonin on these cells were studied. Immunoexpression of S100 protein, GFAP and vimentin were analyzed. Furthermore, the distribution of adrenergic and noradrenergic chromaffin cells subpopulations was studied for the first time in this species. SC present long cytoplasmic processes in contact with chromaffin cells, probably generating an intraglandular communication network. Significant differences (p < 0.05) in the %IA (percentage of immunopositive area) for the S100 protein were observed according to winter (4.21 ± 0.34) and summer (3.51 ± 0.15) values. In castrated animals, the %IA (6.05 ± 0.35) was significantly higher in relation to intact animals (3.95 ± 0.40). In melatonin-treated animals the %IA (3.62 ± 0.23) was significantly higher compared to control animals (2.65 ± 0.26). GFAP immunoexpression was negative and no noradrenergic chromaffin cells were detected suggesting an adrenergic phenotype predominance. Vimentin was observed in SC, endothelial cells and connective tissue. Results indicate that SC exhibit variations along the annual reproductive cycle, along with castration and the melatonin administration. Our results suggest that in this rodent SC are not only support elements, but also participate in the modulation of the activity of the adrenal medulla; probably through paracrine effects.

The quantification of testicular cells during the postnatal development in two Caviomorph rodents: the guinea pig (Cavia porcellus) and the cutia (Dasyprocta agouti)

The germinative, Sertoli and Leydig cells of two caviomorph rodents (Cavia porcellus and Dasyprocta agouti) were counted as well as the estimation of the total volume of the testis and the total volume of seminiferous tubules and interstitium in prepubertal, pubertal and adult animals. The number of spermatogonia, spermatocytes and spermatids cells increased during the pubertal phase in both rodents, notably the spermatid cells. The spermatocyte and spermatid slightly decreased in the adult of both rodents, but the increment in spermatogonia cells number was seen, mainly in cutias. The number of Sertoli cells increased in pubertal rodents, but in the adult the number reduced. Substantial number of Leydig cells was counted in pubertal and adult guinea pigs. In cutias, the number of Leydig cells increased in pubertal phase and decline in adults. The design-based stereological method has proven to be unbiased and reliable to be applied in reproduction studies.

Immunolocalization of proteins in the spermatogenesis process of canine

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

Non-Breeding Eusocial Mole-Rats Produce Viable Sperm--Spermiogram and Functional Testicular Morphology of Fukomys anselli

Ansell’s mole-rats (Fukomys anselli) are subterranean rodents living in families composed of about 20 members with a single breeding pair and their non-breeding offspring. Most of them remain with their parents for their lifetime and help to maintain and defend the natal burrow system, forage, and care for younger siblings. Since incest avoidance is based on individual recognition (and not on social suppression) we expect that non-breeders produce viable sperm spontaneously. We compared the sperm of breeding and non-breeding males, obtained by electroejaculation and found no significant differences in sperm parameters between both groups. Here, we used electroejaculation to obtain semen for the first time in a subterranean mammal. Spermiogram analysis revealed no significant differences in sperm parameters between breeders and non-breeders. We found significantly larger testes (measured on autopsies and on living animals per ultrasonography) of breeders compared to non-breeders (with body mass having a significant effect). There were no marked histological differences between breeding and non-breeding males, and the relative area occupied by Leydig cells and seminiferous tubules on histological sections, respectively, was not significantly different between both groups. The seminiferous epithelium and to a lesser degree the interstitial testicular tissue are characterized by lesions (vacuolar degenerations), however, this feature does not hinder fertilization even in advanced stages of life. The continuous production of viable sperm also in sexually abstinent non-breeders might be best understood in light of the mating and social system of Fukomys anselli, and the potential to found a new family following an unpredictable and rare encounter with an unfamiliar female (“provoked or induced dispersal”). Apparently, the non-breeders do not reproduce because they do not copulate but not because they would be physiologically infertile. The significantly increased testes volume of breeding males (compared to non-breeders) is in agreement with previously found higher testosterone levels of breeders.