Seasonal Expression of INSL3 and Lgr8/Insl3 Receptor Transcripts Indicates Variable Differentiation of Leydig Cells in the Roe Deer Testis

INSL3 Variation in Dogs Following Suppression and Recovery of the HPG Axis

Insulin-like peptide 3 (INSL3) is a constitutive product of mature, adult-type Leydig cells of the testes and consequently in most mammals is an ideal biomarker with which to monitor pubertal development. A new heterologous time-resolved fluorescence immunoassay was developed and validated to measure circulating INSL3 in the blood of adult male dogs. Compared to other species, INSL3 concentration is low with marked variation between individuals, which appears to be independent of breed, age, or weight. A model system was then used in which a cohort of beagle dogs was subject to a GnRH-agonist implant to suppress the HPG axis and spermatogenesis, followed by implant removal and recovery. Unlike testosterone, INSL3 levels were not fully suppressed in all animals by the GnRH agonist, nor was the recovery of Leydig cell function following implant removal uniform or complete, even after several weeks. In dogs, and dissimilar from other species (including humans), Leydig-cell INSL3 appears to be quite variable between individual dogs and only weakly connected to the physiology of the HPG axis after its suppression by a GnRH-agonist implant and recovery. Consequently, INSL3 may be less useful in this species for the assessment of testis function.

Senescence and autophagy relation with the expressional status of non-canonical estrogen receptors in testes and adrenals of roe deer (Capreolus capreolus) during the pre-rut period

The roe deer bucks represent a spontaneous model to study the synchronized testicular involution and recrudescence cycles. However, cellular processes and hormonal control of steroidogenic glands are scarcely known. For the present study testes and adrenal glands obtained from roe deer during the pre-rut season were used. We aimed to determine (i) senescence and autophagy involvement in testis atrophy (immunohistochemical analysis for tumor suppressor protein encoded by the cyclin-dependent kinase inhibitor 2A; p16 and microtubule-associated protein 1A/1B-light chain 3; LC3, respectively), (ii) the size of the adrenal cortex and medulla (morphometric analysis), (iii) G-protein coupled estrogen receptor (GPER) and estrogen-related receptors (ERRs; type α, β, and Y) distribution and expression (qRT-PCR and immunohistochemical analyses) and (iv) serum testosterone and estradiol levels (immunoassay ELISA). This study revealed pre-rut characteristics of testis structure with the presence of both senescence and autophagy-positive cells and higher involvement of senescence, especially in spermatogenic cells (P < 0.05). In the adrenal cortex, groups of cells exhibiting shrinkage were observed. The presence of ERRs in cells of the seminiferous epithelium and interstitial Leydig cells and GPER presence distinctly in Leydig cells was revealed. In adrenals, these receptors were localized in groups of normal-looking cells and those with shrinkage. Morphometric analysis showed differences in cortex width which was smaller (P < 0.05) than that of the medulla. A weak immunohistochemical signal was observed for ERRβ when compared to ERRα and ERRγ. The mRNA expression level of ERRα and ERRγ was lower (P < 0.001 and P < 0.05, respectively) while ERRβ was higher (P < 0.001) in adrenals when compared to testes. mRNA GPER expression was similar in both glands. In the pre-rut season, the testosterone level was 4.89 ng/ml while the estradiol level was 0.234 ng/ml. We postulate that: (i) senescence and autophagy may be involved in both reinitiation of testis function and/or induction of abnormal processes, (ii) hormonal modulation of testis inactivity may affect adrenal cortex causing cell shrinkage, (iii) ERRs and GPER localization in spermatogenic cells and interstitial cells, as well as cortex cells, may maintain and control the morpho-functional status of both glands, and (iv) androgens and estrogens (via ERRs and GPER) drive cellular processes in the testis and adrenal pre-rut physiology.

Functions of somatic cells for spermatogenesis in stallions

Spermatogenesis and testis development are highly structured physiological processes responsible for post-pubertal fertility in stallions. Spermatogenesis comprises spermatocytogenesis, meiosis, and spermiogenesis. Although germ cell degeneration is a continuous process, its effects are more pronounced during spermatocytogenesis and meiosis. The productivity and efficiency of spermatogenesis are directly linked to pubertal development, degenerated germ cell populations, aging, nutrition, and season of the year in stallions. The multiplex interplay of germ cells with somatic cells, endocrine and paracrine factors, growth factors, and signaling molecules contributes to the regulation of spermatogenesis. A cell-to-cell communication within the testes of these factors is a fundamental requirement of normal spermatogenesis. A noteworthy development has been made recently on discovering the effects of different somatic cells including Leydig, Sertoli, and peritubular myoid cells on manipulation the fate of spermatogonial stem cells. In this review, we discuss the self-renewal, differentiation, and apoptotic roles of somatic cells and the relationship between somatic and germ cells during normal spermatogenesis. We also summarize the roles of different growth factors, their paracrine/endocrine/autocrine pathways, and the different cytokines associated with spermatogenesis. Furthermore, we highlight important matters for further studies on the regulation of spermatogenesis. This review presents an insight into the mechanism of spermatogenesis, and helpful in developing better understanding of the functions of somatic cells, particularly in stallions and would offer new research goals for developing curative techniques to address infertility/subfertility in stallions.

Comparison of miRNA and mRNA Expression in Sika Deer Testes With Age

To elucidate the complex physiological process of testis development and spermatogenesis in Sika deer, this study evaluated the changes of miRNA and mRNA profiles in the four developmental stages of testis in the juvenile (1-year-old), adolescence (3-year-old), adult (5-year-old), and aged (10-year-old) stages. The results showed that a total of 198 mature, 66 novel miRNAs, and 23,558 differentially expressed (DE) unigenes were obtained; 14,918 (8,413 up and 6,505 down), 4,988 (2,453 up and 2,535 down), and 5,681 (2,929 up and 2,752 down) DE unigenes, as well as 88 (43 up and 45 down), 102 (44 up and 58 down), and 54 (18 up and 36 down) DE miRNAs were identified in 3- vs. 1-, 5- vs. 3-, and 10- vs. 5-year-old testes, respectively. By integrating miRNA and mRNA expression profiles, we predicted 10,790 mRNA-mRNA and 69,883 miRNA-mRNA interaction sites. The target genes were enriched by GO and KEGG pathways to obtain DE mRNA (IGF1R, ALKBH5, Piwil, HIF1A, BRDT, etc.) and DE miRNA (miR-140, miR-145, miR-7, miR-26a, etc.), which play an important role in testis development and spermatogenesis. The data show that DE miRNAs could regulate testis developmental and spermatogenesis through signaling pathways, including the MAPK signaling pathway, p53 signaling pathway, PI3K-Akt signaling pathway, Hippo signaling pathway, etc. miR-140 was confirmed to directly target mutant IGF1R-3'UTR by the Luciferase reporter assays. This study provides a useful resource for future studies on the role of miRNA regulation in testis development and spermatogenesis.

Genomic Uniqueness of Local Sheep Breeds From Morocco

Sheep farming is a major source of meat in Morocco and plays a key role in the country's agriculture. This study aims at characterizing the whole-genome diversity and demographic history of the main Moroccan sheep breeds, as well as to identify selection signatures within and between breeds. Whole genome data from 87 individuals representing the five predominant local breeds were used to estimate their level of neutral genetic diversity and to infer the variation of their effective population size over time. In addition, we used two methods to detect selection signatures: either for detecting selective sweeps within each breed separately or by detecting differentially selected regions by contrasting different breeds. We identified hundreds of genomic regions putatively under selection, which related to several biological terms involved in local adaptation or the expression of zootechnical performances such as Growth, UV protection, Cell maturation or Feeding behavior. The results of this study revealed selection signatures in genes that have an important role in traits of interest and increased our understanding of how genetic diversity is distributed in these local breeds. Thus, Moroccan local sheep breeds exhibit both a high genetic diversity and a large set of adaptive variations, and therefore, represent a valuable genetic resource for the conservation of sheep in the context of climate change.

Physiology and evolution of the INSL3/RXFP2 hormone/receptor system in higher vertebrates

Although the insulin-like peptide hormone INSL3 and its cognate receptor RXFP2 (relaxin-family peptide receptor 2) have existed throughout chordate evolution, their physiological diversification appears to be linked closely with mammalian emergence and radiation. In contrast, they have been lost in birds and reptiles. Both hormone and receptor are expressed from autosomal genes which have maintained their synteny across vertebrate evolution. Whereas the INSL3 gene comprises only two exons closely linked to the JAK3 gene, RXFP2 is normally encoded by 18 exons. Both genes, however, are subject to alternative splicing to yield a variety of possibly inactive or antagonistic molecules. In mammals, the INSL3-RXFP2 dyad has maintained a probably primitive association with gametogenesis, seen also in fish, whereby INSL3 promotes the survival, growth and differentiation of male germ cells in the testis and follicle development in the ovary. In addition, however, the INSL3/RXFP2 system has adopted a typical 'neohormone' profile, essential for the promotion of internal fertilisation and viviparity; fetal INSL3 is essential for the first phase of testicular descent into a scrotum, and also appears to be associated with male phenotype, in particular horn and skeletal growth. Circulating INSL3 is produced exclusively by the mature testicular Leydig cells in male mammals and acts as a potent biomarker for testis development during fetal and pubertal development as well as in ageing. As such it can be used also to monitor seasonally breeding animals as well as to investigate environmental or lifestyle conditions affecting development. Nevertheless, most information about INSL3 and RXFP2 comes from a very limited selection of species; it will be especially useful to gain further information from a more diverse range of animals, especially those whose evolution has led them to express unusual reproductive phenotypes.

Serum concentrations and testicular expressions of insulin-like peptide 3 and Anti-Müllerian hormone in normal and cryptorchid male horses

Insulin-like peptide 3 (INSL3) is an important hormone for testicular descent during embryonic development and a factor for assessing functional status of Leydig cells of testes, but there is limited number of equine studies. Anti-Müllerian hormone (AMH) is a useful diagnostic marker for cryptorchidism in horses. This study aimed to compare serum concentrations and testicular expression intensity of INSL3 and AMH in intact and cryptorchid male horses. Serum INSL3 concentrations in intact (n = 9; mean ± SEM, 19.9 ± 5.9 ng/mL) and noncastrated unilateral cryptorchid (UC) male horses (n = 16; mean ± SEM, 16.8 ± 4.1 ng/mL) were higher compared with hemicastrated unilateral cryptorchid (HCUC) male horses (n = 9; mean ± SEM, 3.8 ± 0.7 ng/mL) (P < 0.05). And serum INSL3 in bilateral cryptorchid (BC) male horses (n = 4; 1.9 ± 0.4; mean ± SEM, ng/mL) were lower compared with intact male horses (P < 0.05). Serum AMH concentrations in BC male horses (n = 3; mean ± SEM, 30.6 ± 4.8 ng/mL) were higher compared with intact male horses (n = 5; mean ± SEM, 12.2 ± 3.9 ng/mL) (P < 0.05). Immunostaining of scrotal and cryptorchid testis showed that Sertoli cells were positive for AMH, and Leydig cells were positive for INSL3. Staining intensity of AMH was higher in cryptorchid testis than in scrotal testis (P < 0.05). Furthermore, AMH expression intensity was higher in abdominal testis than in inguinal testis (P < 0.05). Immunostaining intensity of INSL3 in the testis was positively correlated with serum INSL3 (r, 0.7; P < 0.01), seminiferous tubule area (r, 0.727; P < 0.01), and Johnsen score for spermatogenesis (r, 0.604; P < 0.05), whereas immunostaining intensity of AMH in the testis was negatively correlated with seminiferous tubule area (r, -0.814; P < 0.01) and Johnsen score for spermatogenesis (r, -0.807; P < 0.01). Our findings suggested that AMH is a good biomarker for diagnosing cryptorchidism in male horses, in addition to INSL3 values to assess the testis of intact and cryptorchid male horses.

Uncovering the Physiological Mechanisms Underlying the Roe Deer (Capreolus capreolus) Testicular Cycle: Analyses of Gelatinases and VEGF Patterns and Correlation with Testes Weight and Testosterone

Simple Summary

The roe deer (Capreolus capreolus) is a wild, small ruminant common in Europe and Asia with a peculiar reproductive cycle. The adult male shows a complete suspension of spermatozoa production during the winter that start again in spring with the peak of sexual activity in summer (July–August). The physiological mechanism underlying such a cycle is yet to be clarified. The work aimed at the analysis of some molecules, like gelatinases (MMP) and vascular growth factor, physiologically involved in tissue remodeling, in roe deer samples collected before (June–July) and after (August–September) the rutting period. Samples were provided by hunters of the Bologna Apennines area (Italy) according to the regional hunting plan. The result showed a post-rut reduction of testicular weight and testosterone, indicative of testes involution, correlated with an increase in pro-MMP2, the latent gelatinase capable of sustaining spermatogenesis once activated. It can be assumed that gelatinases are involved in the testicular cycle and start accumulating after the rutting period to be then activated in preparation of the next reproductive season inducing spermatozoa development and migration. Future studies on this pathway during all seasonal testicular cycles will provide more information about the interesting reproductive physiology of roe deer.

Abstract

The roe deer (Capreolus capreolus) represents a spontaneous model of testicular inactivation: During winter, bucks show a suspension of spermatogenesis that starts again in spring and peaks during the breeding season (July–August). The underlying mechanisms to the regulation of the cyclic testicular changes are still not fully clear but seem to be imputable to the spermatogenic cell line since other testicular cell populations remain stable without apoptotic phenomena. The aim of the study was to investigate apoptosis, gelatinases (MMP2 and 9), their inhibiting factors (TIMP 1-2), and two isoforms of vascular endothelial growth factor (VEGF121 and 165) with its receptors (VEGFR1-2) in testes collected during pre- and post-rut periods, and to correlate them with testicular weight (TW) and testosterone (TEST). Testes from 18 adult sexually mature bucks were collected in Bologna Apennines (Italy). Samples were weighed and parenchyma collected. Radioimmunoassay, real-time PCR, and zymography were performed. The results showed a post-rut decrease in TW and TEST and an increase in proMMP2, also highlighting a correlation between the gelatinases and the testicular functionality. The VEGF pattern did not show modifications nor correlation with TW and TEST. Overall, gelatinases and their inhibitors, described herein for the first time in roe deer testes, seem to play an important role in the testicular cycle.

Mass Spectrometry Supports That the Structure of Circulating Human Insulin-Like Factor 3 Is a Heterodimer

The structure of the testicular peptide hormone insulin-like factor 3 (INSL3) has been the subject of discussion for more than a decade. Some studies support that the central C-domain of INSL3 is proteolytically removed and that INSL3 is secreted by the testicular Leydig cells into circulation as a small heterodimer consisting of an A- and a B-chain linked by two disulfide bridges. Other studies support that the INSL3 peptide remains uncleaved and that the predominant structure of circulating INSL3 is the larger pro-form. Furthermore, the structure of INSL3 could differ between species, and both structural forms of INSL3 could, in principle, be present in circulation. Recently, we have developed a mass spectrometry (MS)-based method for INSL3 in human serum that provides new information about the structure of circulating INSL3. Based on recent and newly presented data, we argue that in healthy men, the common, and probably the only, form of circulating INSL3 is the smaller AB heterodimer. For the first time, we demonstrate that the same analytical principle, with slight modifications, can also be applied to sera from other species, and we show that the INSL3 AB heterodimer is also present in serum from rodents. Improved understanding of the structure and biochemistry of circulating INSL3 could be valuable for the interpretation of INSL3 as a marker for reproductive and developmental disorders in humans and domesticated animals.

Prepubertal nutrition alters Leydig cell functional capacity and timing of puberty

Leydig cell functional capacity reflects the numbers and differentiation status of the steroidogenic Leydig cells in the testes and becomes more or less fixed in early adulthood with the final establishment of the hypothalamo-pituitary-gonadal (HPG) axis after puberty. Factors influencing Leydig cell functional capacity and its role in puberty are poorly understood. Using a bovine model of dairy bulls fed four different nutritional regimes from 1 month to 12 months, and applying circulating Insulin-like peptide 3 (INSL3) as an accurate biomarker of Leydig cell functional capacity, showed that a high plane of nutrition in the first 6 months of life, but not later, significantly increased INSL3 in young adulthood. Moreover, INSL3 concentration at 4 months indicated a marked differential in early feeding regime and correlated well (negatively) with the timing of puberty, as reflected by the age in days for the first production of an ejaculate with >50 million sperm and >10% forward motility, as well as with testis size at 18 months. Reversing the diet at 6 months was unable to rectify the trend in either parameter, unlike for other parameters such as testosterone, body weight, and scrotal circumference. This study has shown that early prepubertal nutrition is a key factor in the development of Leydig cell functional capacity in early adulthood and appears to be a key driver in the dynamic progression of puberty.

Age related and seasonal changes of plasma concentrations of insulin-like peptide 3 and testosterone from birth to early-puberty in Thoroughbred male horses

The peripheral blood concentrations of insulin-like peptide 3 (INSL3) have been detected in many mammalian species, but the level of INSL3 in horse remains unknown. The objectives were to develop a time-resolved fluorescence immunoassay (TRFIA) to detect INSL3 concentrations from horse blood as well as to determine the age-related and seasonal changes of plasma concentrations of INSL3 and testosterone from birth to early-puberty in Thoroughbred male horse (n = 11). Monthly blood sample and measurement of body weight, height, chest and cannon bone size were done from birth until 16 mo. The TRFIA and EIA were used to measure plasma concentrations of INSL3 and testosterone, respectively. An increase in mean body weight, height, chest and cannon bone size was observed throughout the study. The monthly blood sampling revealed an increase in mean plasma INSL3 concentrations up to 2 mo, followed by a decreasing and increasing pattern until the end of experiment at 16 mo. A high testosterone level was detected at birth followed by a sharp decrease to basal level within 1 mo, maintained low level up to10 mo before a gradual rise until 16 mo. In case of seasonality, there was no difference in mean plasma INSL3 concentrations between breeding (March to September) and non-breeding (October to February) seasons, whereas a higher (P < 0.001) mean plasma testosterone concentrations in the second breeding season compared to non-breeding season was observed. In age categorized group, an increase (P < 0.01) in mean plasma INSL3 concentrations was noticed at pre-puberty (1-12 mo) and early-puberty (13-16 mo) compared to birth, but a lower (P < 0.001) mean plasma testosterone concentrations was observed at pre-puberty compared to birth and early-puberty. In conclusion, a TRFIA was developed to measure INSL3 levels in horse. An increase in plasma concentrations of INSL3 and testosterone were observed with the advancement of age, whereas for testosterone a very lower level was detected at the non-breeding season than in the second breeding season after birth in Thoroughbred male horse. The INSL3 secretions seemed independent of seasonal influence, at least before puberty.

Genetic mechanisms underlying spermatic and testicular traits within and among cattle breeds: systematic review and prioritization of GWAS results

Reduced bull fertility imposes economic losses in bovine herds. Specifically, testicular and spermatic traits are important indicators of reproductive efficiency. Several genome-wide association studies (GWAS) have identified genomic regions associated with these fertility traits. The aims of this study were as follows: 1) to perform a systematic review of GWAS results for spermatic and testicular traits in cattle and 2) to identify key functional candidate genes for these traits. The identification of functional candidate genes was performed using a systems biology approach, where genes shared between traits and studies were evaluated by a guilt by association gene prioritization (GUILDify and ToppGene software) in order to identify the best functional candidates. These candidate genes were integrated and analyzed in order to identify overlapping patterns among traits and breeds. Results showed that GWAS for testicular-related traits have been developed for beef breeds only, whereas the majority of GWAS for spermatic-related traits were conducted using dairy breeds. When comparing traits measured within the same study, the highest number of genes shared between different traits was observed, indicating a high impact of the population genetic structure and environmental effects. Several chromosomal regions were enriched for functional candidate genes associated with fertility traits. Moreover, multiple functional candidate genes were enriched for markers in a species-specific basis, taurine (Bos taurus) or indicine (Bos indicus). For the different candidate regions identified in the GWAS in the literature, functional candidate genes were detected as follows: B. Taurus chromosome X (BTX) (TEX11, IRAK, CDK16, ATP7A, ATRX, HDAC6, FMR1, L1CAM, MECP2, etc.), BTA17 (TRPV4 and DYNLL1), and BTA14 (MOS, FABP5, ZFPM2). These genes are responsible for regulating important metabolic pathways or biological processes associated with fertility, such as progression of spermatogenesis, control of ciliary activity, development of Sertoli cells, DNA integrity in spermatozoa, and homeostasis of testicular cells. This study represents the first systematic review on male fertility traits in cattle using a system biology approach to identify key candidate genes for these traits.

Relaxin-like peptides in male reproduction - a human perspective

The relaxin family of peptide hormones and their cognate GPCRs are becoming physiologically well-characterized in the cardiovascular system and particularly in female reproductive processes. Much less is known about the physiology and pharmacology of these peptides in male reproduction, particularly as regards humans. H2-relaxin is involved in prostate function and growth, while insulin-like peptide 3 (INSL3) is a major product of the testicular Leydig cells and, in the adult, appears to modulate steroidogenesis and germ cell survival. In the fetus, INSL3 is a key hormone expressed shortly after sex determination and is responsible for the first transabdominal phase of testicular descent. Importantly, INSL3 is becoming a very useful constitutive biomarker reflecting both fetal and post-natal development. Nothing is known about roles for INSL4 in male reproduction and only very little about relaxin-3, which is mostly considered as a brain peptide, or INSL5. The former is expressed at very low levels in the testes, but has no known physiology there, whereas the INSL5 knockout mouse does exhibit a testicular phenotype with mild effects on spermatogenesis, probably due to a disruption of glucose homeostasis. INSL6 is a major product of male germ cells, although it is relatively unexplored with regard to its physiology or pharmacology, except that in mice disruption of the INSL6 gene leads to a disruption of spermatogenesis. Clinically, relaxin analogues may be useful in the control of prostate cancer, and both relaxin and INSL3 have been considered as sperm adjuvants for in vitro fertilization.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Circannual Testis Changes in Seasonally Breeding Mammals

In the non-equatorial zones of the Earth, species concentrate their reproductive effort in the more favorable season. A consequence of seasonal breeding is seasonal testis regression, which implies the depletion of the germinative epithelium, permeation of the blood-testis barrier, and reduced androgenic function. This process has been studied in a number of vertebrates, but the mechanisms controlling it are not yet well understood. Apoptosis was assumed for years to be an important effector of seasonal germ cell depletion in all vertebrates, including mammals, but an alternative mechanism has recently been reported in the Iberian mole as well as in the large hairy armadillo. It is based on the desquamation of meiotic and post-meiotic germ cells as a consequence of altered Sertoli-germ cell adhesion molecule expression and distribution. Desquamated cells are either discarded alive through the epididymis, as in the mole, or subsequently die by apoptosis, as in the armadillo. Also, recent findings on the reproductive cycle of the greater white-toothed shrew at the meridional limits of its distribution area have revealed that the mechanisms controlling seasonal breeding are in fact far more plastic and versatile than initially suspected. Perhaps these higher adaptive capacities place mammals in a better position to face the ongoing climate change.

Expression profiles of relaxin family peptides and their receptors indicate their influence on spermatogenesis in the domestic cat (Felis catus)

Disturbed spermatogenesis is a common problem in felines. Studying spermatogenesis in the domestic cat can improve the understanding of the biological background and help to counteract fertility problems in other feline species. Here, we analyzed 3 relaxin family peptides (relaxin, relaxin-3, and INSL3) and their receptors (RXFP1, RXFP2, and RXFP3) as potential spermatogenic factors involving their expression in the testis at different stages of its development. It may be concluded from its stage-dependent expression that relaxin, together with RXFP1, appears to be involved in the first stage of spermatogenesis, whereas relaxin-3 via binding to RXFP3 influences spermiogenesis. Furthermore, correlations were observed between relaxin, relaxin-3, RXFP1, RXFP2 and RXFP3 messenger RNA expression, and the relative numbers of haploid cells in testes. The peptide INSL3 was highly expressed at all testis development stages. Because of the low and stage-independent expression of its receptor RXFP2, an auto- and/or paracrine function of INSL3 in spermatogenesis seems unlikely. In the adult testis, messenger RNA expression of relaxin, RXFP1, and RXFP3 predominantly occurs in the tubular testis compartment, whereas INLS3 is mainly expressed in the interstitium.

Expression of insulin-like factor 3 hormone-receptor system in the reproductive organs of male goats

Relaxin-like factor (RLF), generally known as insulin-like factor 3 (INSL3), is essential for testis descent during fetal development. However, its role in adult males is not fully understood. We investigate the function of INSL3 in male Saanen goats by identifying cell types expressing its receptor, relaxin/insulin-like family peptide receptor (RXFP)2 and by characterizing the developmental expression pattern of INSL3 and RXFP2 and the binding of INSL3 to target cells in the male reproductive system. A highly specific RXFP2 antibody that co-localizes with an anti-FLAG antibody in HEK-293 cells recognizes RXFP2-transcript-expressing cells in the testis. INSL3 and RXFP2 mRNA expression is upregulated in the testis, starting from puberty. INSL3 mRNA and protein expression has been detected in Leydig cells, whereas RXFP2 mRNA and protein localize to Leydig cells, to meiotic and post-meiotic germ cells and to the epithelium and smooth muscle of the cauda epididymis and vas deferens. INSL3 binds to all of these tissues and cell types, with the exception of Leydig cells, in a hormone-specific and saturable manner. These results provide evidence for a functional intra- and extra-testicular INSL3 ligand-receptor system in adult male goats.

Dynamics of insulin-like factor 3 and its receptor expression in boar testes

Relaxin-like factor (RLF), now mainly known as insulin-like factor 3 (INSL3), is essential for testis descent during fetal development; however, its function in the adult testis is still being elucidated. As a major step toward understanding the as-yet-unknown function of INSL3 in boars, this study aimed to develop a time-resolved fluoroimmunoassay for boar INSL3, characterize the dynamics of INSL3 expression during development, and demonstrate the expression of the INSL3 hormone-receptor system in the testis. All samples were collected from Duroc boars. The sensitivity of the assay system established was 8.2 pg/well (164 pg/ml), and no cross-reactivity with other hormones, such as porcine relaxin, was observed. Circulating INSL3 was shown to increase progressively during development. INSL3 secreted from the Leydig cells was released not only into the blood circulation but also into the interstitial and seminiferous compartments in sufficient concentrations. A testicular fractionation study revealed that its receptor RXFP2 transcripts were expressed mainly in testicular germ cells. In addition, INSL3 bound to the germ cell membranes in a hormone-specific and saturable manner. These results reveal that INSL3 secreted into the interstitial compartment from the Leydig cells is transported into the seminiferous compartments, where its receptor RXFP2 is expressed mainly in the germ cells to which INSL3 binds, suggesting that INSL3 functions as a paracrine factor on seminiferous germ cells.

Relaxin family peptides and their receptors

There are seven relaxin family peptides that are all structurally related to insulin. Relaxin has many roles in female and male reproduction, as a neuropeptide in the central nervous system, as a vasodilator and cardiac stimulant in the cardiovascular system, and as an antifibrotic agent. Insulin-like peptide-3 (INSL3) has clearly defined specialist roles in male and female reproduction, relaxin-3 is primarily a neuropeptide involved in stress and metabolic control, and INSL5 is widely distributed particularly in the gastrointestinal tract. Although they are structurally related to insulin, the relaxin family peptides produce their physiological effects by activating a group of four G protein-coupled receptors (GPCRs), relaxin family peptide receptors 1-4 (RXFP1-4). Relaxin and INSL3 are the cognate ligands for RXFP1 and RXFP2, respectively, that are leucine-rich repeat containing GPCRs. RXFP1 activates a wide spectrum of signaling pathways to generate second messengers that include cAMP and nitric oxide, whereas RXFP2 activates a subset of these pathways. Relaxin-3 and INSL5 are the cognate ligands for RXFP3 and RXFP4 that are closely related to small peptide receptors that when activated inhibit cAMP production and activate MAP kinases. Although there are still many unanswered questions regarding the mode of action of relaxin family peptides, it is clear that they have important physiological roles that could be exploited for therapeutic benefit.

Relaxin-like factor (RLF)/insulin-like peptide 3 (INSL3) is secreted from testicular Leydig cells as a monomeric protein comprising three domains B-C-A with full biological activity in boars

RLF (relaxin-like factor), also known as INSL3 (insulin-like peptide 3), is a novel member of the relaxin/insulin gene family that is expressed in testicular Leydig cells. Despite the implicated role of RLF/INSL3 in testis development, its native conformation remains unknown. In the present paper we demonstrate for the first time that boar testicular RLF/INSL3 is isolated as a monomeric structure with full biological activity. Using a series of chromatography steps, the native RLF/INSL3 was highly purified as a single peak in reverse-phase HPLC. MS/MS (tandem MS) analysis of the trypsinized sample provided 66% sequence coverage and revealed a distinct monomeric structure consisting of the B-, C- and A-domains deduced previously from the RLF/INSL3 cDNA. Moreover, the N-terminal peptide was four amino acid residues longer than predicted previously. MS analysis of the intact molecule and PMF (peptide mass fingerprinting) analysis at 100% sequence coverage confirmed this structure and indicated the existence of three site-specific disulfide bonds. RLF/INSL3 retained full bioactivity in HEK (human embryonic kidney)-293 cells expressing RXFP2 (relaxin/insulin-like family peptide receptor 2), the receptor for RLF/INSL3. Furthermore, RLF/INSL3 was found to be secreted from Leydig cells into testicular venous blood. Collectively, these results indicate that boar RLF/INSL3 is secreted from testicular Leydig cells as a B-C-A monomeric structure with full biological activity.

Basal insulin-like factor 3 levels predict functional ovarian hyperandrogenism in the polycystic ovary syndrome

AIM

The aims of the study were to understand the association between insulin-like factor 3 (INSL3) and functional ovarian hyperandrogenism (FOH) in PCOS and the regulatory role played by LH.

SUBJECTS AND METHODS

Fifteen PCOS women were classified as FOH (FOH-PCOS, no.=8) and non-FOH (NFOH-PCOS, no.=7) according to the response of 17OH-progesterone to buserelin (a GnRH analogue) with respect to 15 controls. FOH-PCOS and NFOH-PCOS were compared for basal INSL3 levels. In addition, the effect of buserelin on INSL3 concentrations and the relationship between basal and buserelin-stimulated LH and 17OH-progesterone and INSL3 were evaluated.

RESULTS

Basal INSL3 levels were higher in FOH-PCOS than NFOH-PCOS (p=0.001) and controls (p=0.001), whereas they did not differ between NFOHPCOS and controls. In addition, FOH-PCOS had a higher response of LH to buserelin with respect to NFOH-PCOS. Within all PCOS women the levels of INSL3 positively correlated with free testosterone (p=0.022) and negatively with SHBG (r= p=0.031). Moreover, positive correlations with the absolute increase of 17OH-progesterone (p<0.001) and with the LH area under the curve (p=0.001) after buserelin administration were found. In the multiple regression analysis INSL3 persisted significantly correlated only with 17OH-progesterone response to buserelin. Finally, INSL3 was not significantly modified after buserelin administration either in FOHPCOS or in NFOH-PCOS.

CONCLUSIONS

These data suggest that INSL3 is related to FOH in PCOS women, but this association seems not to be mediated by LH, further reinforcing the concept that a pathophysiological heterogeneity for ovarian hyperandrogenism in PCOS exists.

Human testicular insulin-like factor 3: in relation to development, reproductive hormones and andrological disorders

Knockout of the gene encoding insulin-like factor 3 (INSL3) results in cryptorchidism in mice due to disruption of the transabdominal phase of testicular descent. This finding was essential for understanding the complete course of testis descensus, and wound up years of speculations regarding the endocrine regulation of this process. INSL3 is, along with testosterone, a major secretory product of testicular Leydig cells. In addition to its crucial function in testicular descent, INSL3 is suggested to play a paracrine role in germ cell survival and an endocrine role in bone metabolism. INSL3 is produced in human prenatal and neonatal, and in adult Leydig cells to various extents, and is in a developmental context regulated like testosterone, with production during second trimester, an early postnatal peak and increasing secretion during puberty, resulting in high adult serum levels. INSL3 production is entirely dependent on the state of Leydig cell differentiation, and is stimulated by the long-term trophic effects mediated by luteinizing hormone (LH). Once differentiated, Leydig cells apparently express INSL3 in a constitutive manner, and the hormone is thereby insensitive to the acute, steroidogenic effects of LH, which for example is an important factor in the regulation of testosterone. Clinically, serum INSL3 levels can turn out to be a usable tool to monitor basal Leydig cell function in patients with various disorders affecting Leydig cell function. According to animal studies, foetal INSL3 production is, directly or indirectly, sensitive to oestrogenic or anti-androgenic compounds. This provides important insight into the mechanism by which maternal exposure to endocrine disrupters can result in cryptorchidism in the next generation. Conclusively, INSL3 is an interesting testicular hormone with potential clinical value as a marker for Leydig cell function. It should be considered on a par with testosterone in the evaluation of testicular function and the consequences of Leydig cell dysfunction.

Expression of insulin-like 3 (INSL3) and differential splicing of its receptor in the ovary of rhesus macaques

BACKGROUND

Although insulin-like 3 (INSL3) has been identified in the gonad of both sexes in many species, there are only limited reports on the distribution of INSL3 and its receptor, relaxin/insulin-like family peptide receptor 2 (RXFP2), in the primate ovary. Since the hormone-receptor pair is believed to play a role in female reproduction, investigating the transcription of INSL3/RXFP2 genes and the spatiotemporal expression of INSL3 in the nonhuman primate may shed light on the functional aspects of the system in humans.

METHODS

Database mining, molecular and immunological methods were applied.

RESULTS

One single INSL3 transcript and three novel splice variant transcripts of RXFP2 were identified in the ovary of rhesus macaques. While the full-length RXFP2 transcript is barely detectable in granulosa cells during the periovulatory period, INSL3 transcript and protein are highly abundant in theca cells surrounding antral follicles. Moreover, the INSL3 level in follicular fluid is 3-4 times higher than that in female serum which remains low throughout the menstrual cycle.

CONCLUSIONS

The presence of INSL3 and its receptor in the ovary implies a potential role of the ligand-receptor pair in female reproduction in nonhuman primates. However, the existence of multiple splice variants of RXFP2 indicates a very complex nature of the hormone-receptor system.

Partial cDNA sequence of a relaxin-like factor (RLF) receptor, LGR8 and possible existence of the RLF ligand-receptor system in goat testes

Relaxin-like factor (RLF), also known as insulin-like factor 3 (INSL3), is produced by testicular Leydig cells, but its specific receptor LGR8 (leucine-rich repeat family of G-protein-coupled receptor 8) has not been identified in goats. This study aimed to identify complementary DNA (cDNA) sequences of goat LGR8, and characterize the expression of both RLF and LGR8 in goat testes by RT-PCR and immunohistochemistry. Testes were collected from immature (3-month-old) and mature (24-month-old) Saanen goats, and partial cDNA sequences of the goat homologue of human LGR8 were identified. The sequence encoded a reduced peptide sequence of 167 amino acids, which corresponded to transmembrane regions 2 through 5, followed by the beginning of intracellular loop 3 of human LGR8. Expression of both LGR8 and RLF genes was drastically increased in mature testes compared with immature ones. Although RLF protein was restricted to Leydig cells, LGR8 protein was detected in both Leydig cells and seminiferous epithelial cells (possibly germ cells and Sertoli cells). These results reveal a possible existence of the RLF-LGR8 ligand-receptor system within the goat testis, suggesting that RLF may play a role in testicular function through LGR8 on Leydig cells and seminiferous epithelial cells in an autocrine and/or paracrine manner.

Vascular endothelial growth factor A is a putative paracrine regulator in seasonally controlled spermatogenesis: insights from a ruminant model, the roe deer

Vascular endothelial growth factor A (VEGFA) influences spermatogenesis, but its impact on seasonally regulated sperm production is still not fully understood. Thus, we investigated both expression levels and localisation of VEGFA and its receptors VEGFR1 and 2 in roe buck testis via real-time reverse transcription polymerase chain reaction and immunohistochemistry in relation to seasonal changes in the cellular composition of the testis. VEGFA was expressed by interstitial cells while its receptors were found on endothelial and perivascular cells. Inside the tubules, VEGFA was located in spermatogonia and spermatocytes, VEGFR1 was present on elongating spermatids and VEGFR2 on Sertoli cells. VEGFR1 mRNA was expressed tenfold lower than VEGFR2 and VEGF mRNAs. Relative VEGF and VEGFR2 expression (divided by the number of VEGFA and VEGFR2 expressing cells) showed an increase towards the rut (July/August) and a decrease thereafter. The results suggest involvement of VEGFA in the adjustment of vascular permeability as well as in spermiogenesis and the proliferation of spermatogonia.

Relaxin and related peptides in male reproduction

The relaxin hormone is renowned for its function in pregnancy, parturition and other aspects of female reproduction. At the same time, the role of relaxin in male reproduction is still debated. Relaxin is prominently expressed in prostate and its receptors are found in several male reproductive organs; however, the data indicative of its contribution to differentiation and functioning of prostate or testis are contradictory. Prostate relaxin is a main source of this peptide in the seminal plasma. The relaxin effects on sperm motility and fertilization have been reported. The expression of other relaxin related peptides, such as INSL5 and INSL6 was described in testis; yet, currently there are no experimental data to pinpoint their biological functions. The other member of relaxin peptide family, insulin-like 3 peptide (INSL3), is a major player in male development. The INSL3 peptide is expressed in testicular fetal and adult Leydig cells and is directly responsible for the process of abdominal testicular descent (migration of the testes towards the scrotum during male development). Genetic targeting of the Insl3 gene or INSL3 GPCR receptor Lgr8/Rxfp2 causes high intra-abdominal cryptorchidism due to a differentiation failure of testicular ligaments, the gubernacula. Several mutations of these two genes rendering nonfunctional proteins have been described in human patients with testicular maldescent. Thus, in this chapter we review the data related to the expression and function of relaxin and related peptides in male reproduction.

Directed overexpression of insulin in Leydig cells causes a progressive loss of germ cells

The primary goal of this study was to determine the 5'region of the Insl3 gene that specifically targets the expression of human insulin to Leydig cells, and to explore whether the testicular proinsulin is efficiently processed to insulin that is able to rescue the diabetes in different mouse models of diabetes. We show here that the sequence between nucleotides -690 and +4 of mouse Insl3 promoter is sufficient to direct the Leydig cell-specific expression of the human insulin transgene (Insl3-hIns). We also found that the 3'untranslated region (3'UTR) of Insl3 was effective in enhancing transgene expression of the insulin in vivo. Expression analysis revealed that the temporal expression pattern of the hIns transgene in Leydig cells of transgenic testes is roughly the same as that of the endogenous Insl3. Despite the Leydig cells translate human proinsulin and secrete a significant level of free C-peptide into the serum, the Leydig cell-derived insulin is not able to overcome the diabetes in different mouse models of diabetes, suggesting a lack of glucose sensing mechanisms in the Leydig cells. A consequence of overexpression of the human proinsulin in Leydig cells was the decrease of fertility of transgenic males at older ages. Germ cells in transgenic males were able to initiate and complete spermatogenesis. However, there was a progressive and age-dependent degeneration of the germ cells that lead to male infertility with increasing age.

Estrogens are involved in seasonal regulation of spermatogenesis and sperm maturation in roe deer (Capreolus capreolus)

Roe deer (a seasonal breeder, rut: July to August) is a well characterized model for studying the seasonal regulation of testicular activity. However, not much is known about the impact of estrogens on seasonally determined sperm production. We therefore explored the time and cell type specific expression of estrogen receptors and of enzymes involved in steroid biosynthesis in roe deer testicular parenchyma and in the epididymis. Every second month during the entire seasonal cycle five roe bucks were castrated (n=30). Estrogen receptor (ER) alpha, ERbeta and the enzymes P450Aromatase and P450C17 were localized immunohistochemically. The expression levels of ERalpha, ERbeta and P450Aromatase were evaluated by semi-quantitative Western blot. Contrary to the enzyme required for androgen production (P450C17), which is expectedly located only in the Leydig cells and shows an expression increase towards rutting season, a seasonal expression difference of the enzyme required for the conversion into oestradiol (P450Aromatase) is visible only in the epididymis. In the testis, ERalpha expression shows a striking dependency on tubular cell composition, and the single cell expression activity increases towards rut. This implicates that estrogens are directly involved in the regulation of spermatogenesis in the roe buck. In the epididymis, expression of ERalpha is seasonally determined particularly in the ductuli efferentes. ERbeta was detected throughout the year with no distinct dependency on season or the stages of germinative epithelium cycle. We conclude that estrogens in the roe buck influence the seasonally determined sperm production predominantly by the regulated expression of ERalpha.

Expression of insulin-like peptide 3 in the postnatal rat Leydig cell lineage: timing and effects of triiodothyronine-treatment

Fetal (FLC) and adult Leydig cells (ALC) secrete insulin-like peptide 3 (INSL3), which is linked to cryptorchidism in the newborn rat. Its gene regulation appears to be independent of that for most steroidogenic enzymes, and may thus be a marker for other aspects of ALC differentiation. Our study examined the following on INSL3 peptide expression in ALC lineage (i) timing, (ii) which cell stage, and (iii) effects of triiodothyronine (T3). Male Sprague-Dawley (SD) rats of postnatal days (pd) 1, 5, 7-21, 28, 40, 60, and 90 were used for the objectives (i) and (ii). For the objective (iii), control and T3-treated (daily T3 SC, 50 mug/kg bw) SD rats of pd7-16 and 21 were used. INSL3 was immunolocalized in Bouin's-fixed testes. FLC were positive and mesenchymal and Leydig progenitor cells were negative for INSL3 at tested ages. INSL3 in ALC lineage was first detected in newly formed ALC on pd16, although they were present from pd10. The intensity of INSL3 label was greater in ALC of pd40-90. ALC were present in T3-treated testes at pd9, but INSL3 first detected in them was on pd12. While INSL3 in FLC regulates testicular descent, INSL3 in ALC still has no well-defined function. However, its pattern of expression correlates temporally with the development of steroidogenic function and spermatogenesis. Thus, the delay between ALC differentiation and INSL3 expression in them implies that INSL3 in ALC is associated with maturation. The advancement of INSL3 expression in the ALC of T3-treated rats implies that this function is established earlier with T3-treatment.

Insulin-like factor 3: a new circulating hormone related to luteinizing hormone-dependent ovarian hyperandrogenism in the polycystic ovary syndrome

CONTEXT

Insulin-like factor 3 (INSL3), a member of the relaxin-insulin family, is produced in the Leydig cells and at reduced levels in ovarian theca interna cells of antra follicles as well as in the corpora lutea and ovarian stroma. Among the factors potentially involved in the stimulation of gonadal expression of INSL3, recent data obtained in rats show an important role of LH. Ovaries from most women affected by polycystic ovary syndrome (PCOS) are characterized by hyperplasia of the theca interna and of cortical stroma and by an increased number of small antral follicles, and the majority of women with PCOS, particularly normal-weight subjects, have LH levels that are above the normal range.

OBJECTIVE

The objective of this study was to investigate INSL3 circulating levels in both normal-weight and overweight-obese PCOS women and the association of INSL3 with gonadotropin and androgenic pattern and with ovarian morphology.

DESIGN

This was a controlled study.

SETTING

The study took place at an academic hospital.

PARTICIPANTS

The participants included 44 PCOS patients (22 normal-weight and 22 overweight-obese) and 44 controls comparable for age and body weight.

MAIN OUTCOME MEASURES

The main outcome measures included INSL3 serum concentrations, measured by RIA, in PCOS patients and controls and their correlation with clinical and biochemical phenotype and with ovarian morphology.

RESULTS

INSL3 serum concentrations were significantly higher in PCOS patients with respect to controls (P = 0.003), particularly in normal-weight (P = 0.001) but not in overweight-obese (P = 0.312) PCOS patients. INSL3 serum concentrations were positively correlated with total and free testosterone and with LH levels in all women (total testosterone, P < 0.001; free testosterone, P = 0.001; LH, P = 0.002) as well as in PCOS patients (total testosterone, P = 0.024; free testosterone, P = 0.045; LH, P = 0.049). Moreover, in the PCOS group, INSL3 levels were related to a greater 17OH-progesterone response to buserelin (P = 0.015), an index of ovarian hyperandrogenism. Finally, in PCOS women, INSL3 levels were positively correlated with ovarian follicle number (P = 0.028).

CONCLUSIONS

INSL3 could be considered a new circulating hormone related to LH-dependent ovarian hyperandrogenism, particularly in normal-weight PCOS women.

Peripheral INSL3 concentrations decline with age in a large population of Australian men

The novel peptide hormone insulin-like peptide 3 (INSL3) is a major secretory product of the Leydig cells of the testis, and in adult men is secreted into the blood, giving rise to circulating concentrations ranging from 0.5 to 2.5 ng/mL. We studied a large randomly recruited cohort of 1183 men from South Australia, comparing serum INSL3 concentrations with age, and a variety of endocrine, cognitive and morphological parameters. While INSL3 concentration declines significantly (p < 0.001) and continuously with age from 1.29 +/- 0.47 ng/mL in young men (age 35-44 years) to 0.79 +/- 0.39 ng/mL in the age group 75-80 years, there is no correlation with testosterone or components of the hypothalamo-pituitary-gonadal (HPG) axis, independent of age, nor with any other parameter measured, including thyroid or prostate status and obesity. For men exhibiting normal follicle stimulating hormone (FSH) and high luteinizing hormone (LH) levels, there was a significant inverse correlation with plasma oestradiol. Unilaterally orchidectomized men had INSL3 values intermediate between intact men and anorchid subjects, and showed inverse correlations (p < 0.001) between INSL3 and FSH or LH concentrations, which were independent of age. Taken together, the data show that INSL3 is an independent measure of Leydig cell function (quality and number), which appears to be independent of acute control via the HPG axis. Its decline with age reflects a decline in the properties of the Leydig cell population only, and emphasizes a gonadal component in the age-related decrease in androgen production.

Changes in serum insulin-like factor 3 during normal male puberty

CONTEXT

Insulin-like factor 3 (INSL3) is produced by the Leydig cells, and in adults, its secretion is dependent on the state of differentiation of these cells, which, in turn, is dependent on LH. However, the secretion and regulation of INSL3 during puberty is unknown.

OBJECTIVE

Our objective was to evaluate INSL3 concentrations during normal male puberty and the relation of INSL3 to LH, FSH, and testosterone.

DESIGN AND SETTING

We conducted a cross-sectional study from January to December 2005 at academic clinics.

PATIENTS

Participating in the study were 75 healthy male subjects aged 9.5-17.5 yr, homogeneously distributed into five pubertal groups of 15 according to Tanner stages.

MAIN OUTCOME MEASURES

We assessed mean testicular volume and LH, FSH, testosterone, and INSL3 concentrations in relation to age and pubertal stage.

RESULTS

We observed an increase of INSL3 and LH levels from Tanner stage 2 to 4, and an increase of FSH from stage 2 to 3. Testosterone levels increased from stage 3 to 4. No differences were seen for all measured hormones between stages 4 and 5. The increase in INSL3 seemed therefore to anticipate the increase in testosterone. However, INSL3 plasma concentrations at pubertal stages 4 and 5 are about one fourth of adult levels, whereas FSH, LH, and testosterone reached adult levels by stage 4. Positive significant correlations were found between INSL3 and LH for all pubertal stages.

CONCLUSIONS

This study provides information on the physiological dynamics of INSL3, showing that the serum concentrations of this hormone increased progressively throughout puberty under the differentiating action of LH on Leydig cells. INSL3 is therefore confirmed to represent a marker of Leydig cell differentiation and function. However, a prolonged exposure to LH seems to be necessary to reach INSL3 concentrations of adults. A possible use of INSL3 in puberty disorders is promising.

Paracrine and endocrine roles of insulin-like factor 3

Insulin-like factor 3 (INSL3) is expressed in Leydig cells of the testis and theca cells of the ovary. This peptide affects testicular descent by acting on gubernaculum via its specific receptor leucine-rich repeat-containing G protein-coupled receptor 8 (LGR8). From initial animal data showing the cryptorchid phenotype of Insl3/Lgr8 mutants, an extensive search for mutations in INSL3 and LGR8 genes was undertaken in human patients with cryptorchidism, and a frequency of mutation of 4-5% has been detected. However, definitive proofs of a causative role for some of these mutations are still lacking. More recent data suggest additional paracrine (in the testis and ovary) and endocrine actions of INSL3 in adults. INSL3 circulates at high concentrations in serum of adult males and its production is dependent on the differentiation effect of LH. Therefore, INSL3 is increasingly used as a specific marker of Leydig cell differentiation and function.

Insulin-Like Factor 3: Where Are We Now?

Insulin-like factor 3 (INSL3), previously known as the relaxin-like factor (RLF), is a major peptide hormone secreted from the testicular Leydig cells of adult men and circulating in the blood at a concentration of approximately 1 ng/mL. Women also produce INSL3 in the theca interna cells of ovarian follicles, but circulating levels remain below 100 pg/mL. INSL3 is structurally related to relaxin and insulin, but unlike the latter, signals through a novel G-protein-coupled receptor, LGR8. Ablation of the gene for INSL3 leads primarily to cryptorchidism because of a defect in the first, transabdominal phase of testicular descent. In the adult knockout mouse, a mild phenotype is evident in the testis and ovary. We have developed a panel of antibodies specific for INSL3 from various species, which are suitable for immunohistochemistry and, more recently, for immunoassays. INSL3 is an important marker for the mature Leydig cell phenotype, where it appears to be expressed constitutively, once the mature differentiation state is achieved. It is also an indicator of differentiation status not only for Leydig cells but also for the theca interna cells of the ovary.

The roe deer as a model for studying seasonal regulation of testis function

In mature male seasonal breeders, the circannual cycles of testicular growth and involution involve significant changes in structure and function of both the tubular and interstitial testicular compartment. Roe deer (Capreolus capreolus) are seasonal breeders with a short defined rutting season from mid-July to mid-August and represent a unique non-rodent model for studying testicular functions during the course of a complete reproductive cycle with naturally changing photoperiod. Germ cells and Sertoli cells of the seminiferous tubules and the interstitial Leydig cells all display significant morphological and physiological alterations during the seasonal changes. In contrast to the germ cell population, Sertoli and Leydig cells persist as a numerically constant cell population in the roe deer testis. This report emphasizes the intricate relationship between seasonal cellular differentiation, intratesticular growth factor networks and their impact on the functional dynamics during the seasonal changes in roe deer testis.

Insulin-like factor 3: a novel circulating hormone of testicular origin in humans

Insulin-like factor 3 (INSL3) affects testicular descent. Mutations in the INSL3 gene or its receptor, LGR8/GREAT, can cause cryptorchidism. Expression of LGR8/GREAT in different tissues and production of INSL3 by adult-type Leydig cells suggest additional roles for this hormonal system in adults. We used a novel radioimmunoassay kit to measure INSL3 concentrations in the serum of normal men and those with different testicular pathologies. We demonstrate that INSL3 circulates in adult men and is almost exclusively of testicular origin. Subjects with severe testicular damage (infertility) produce small amounts of INSL3, and concentrations of this hormone seem to reflect the functional status of the Leydig cells. Analysis of men treated with different combinations of hormones of the hypothalamus-pituitary-testis axis suggests that the production of INSL3 is related to the luteinizing hormone.

Constitutive regulation of the Insl3 gene in rat Leydig cells

Insulin-like factor 3 (Insl3) is a major new product of the Leydig cells in all mammalian species so far examined. The rat Insl3 gene is encoded by two exons in close juxtaposition to the Jak3 gene. Using RT-PCR analysis we now show that in the rat testis it is expressed as both major and minor splice variants, the former encoding the normal protein, the latter a truncated peptide comprising a C-terminally extended B-domain. Both transcripts are produced in constant relative amounts uniquely in the Leydig cells of the postnatal testis and in no other testicular cell type. Rat Insl3 protein is also expressed only in Leydig cells after postnatal day 30. Although specific mRNA is present at earlier times, corresponding protein is not detected. Semi-quantitative RT-PCR analysis of Insl3 transcripts in the mouse MA-10 tumour Leydig cell-line under a wide range of stimulation regimes shows that in an acute context, the Insl3 gene is expressed absolutely constitutively. This is confirmed by transfection and electrophoretic mobility shift (EMSA) analysis of the rat Insl3 gene promoter, wherein the importance of three putative SF-1 responsive elements is underscored, although these appear to differ in their relative importance from their counterparts in the mouse Insl3 gene.

Minimal activity in both proliferation and apoptosis of interstitial cells indicates seasonally persisting Leydig cell population in roe deer

Seasonally regulated breeding is associated with significant changes in testis mass, structure and function. This includes the variation in size, structure and function of the Leydig cells. Recently, interstitial cells have been characterised as a numerically constant population in roe deer. However, no consistent data are available regarding changes in the number of Leydig cells, their differentiation or turnover in seasonally breeding mammals. This study has quantified the numbers of both proliferating and apoptotic cells in roe deer testis bimonthly during a complete annual cycle. Proliferation was detected by immunolocalisation of PCNA and Ki-67 in tissue sections, whereas apoptosis was localised by the TUNEL technique and an antibody to caspase-3. The labelled cells were counted by using a computer-aided image-analysing system. The number of proliferating spermatogenic cells per tubule cross section showed seasonal changes with a maximum in April (14.9+/-0.6) and a subsequent decline up to December (1.6+/-0.3). Percentages of positive cells per square millimetre of interstitial area were below 1% throughout the year. The average number of apoptotic cells per tubule cross section was low and varied only between 0.5 and 1.4 (caspase-3) or 0.1 and 2.1 (TUNEL). In the interstitial compartment, only a few apoptotic cells (<or=0.7%) were found sporadically scattered within the intertubular region during all studied seasonal periods. The results suggest that a constant total number of interstitial cells arise from a conserved cell population of changing functional state rather than from a steady-state population with a definite turnover of cells during seasonal changes in testicular activity.