Sexual dimorphism in the neonatal gonad

Transcriptomic responses to environmental temperature by turtles with temperature-dependent and genotypic sex determination assessed by RNAseq inform the genetic architecture of embryonic gonadal development

Vertebrate sexual fate is decided primarily by the individual's genotype (GSD), by the environmental temperature during development (TSD), or both. Turtles exhibit TSD and GSD, making them ideal to study the evolution of sex determination. Here we analyze temperature-specific gonadal transcriptomes (RNA-sequencing validated by qPCR) of painted turtles (Chrysemys picta TSD) before and during the thermosensitive period, and at equivalent stages in soft-shell turtles (Apalone spinifera-GSD), to test whether TSD's and GSD's transcriptional circuitry is identical but deployed differently between mechanisms. Our data show that most elements of the mammalian urogenital network are active during turtle gonadogenesis, but their transcription is generally more thermoresponsive in TSD than GSD, and concordant with their sex-specific function in mammals [e.g., upregulation of Amh, Ar, Esr1, Fog2, Gata4, Igf1r, Insr, and Lhx9 at male-producing temperature, and of β-catenin, Foxl2, Aromatase (Cyp19a1), Fst, Nf-kb, Crabp2 at female-producing temperature in Chrysemys]. Notably, antagonistic elements in gonadogenesis (e.g., β-catenin and Insr) were thermosensitive only in TSD early-embryos. Cirbp showed warm-temperature upregulation in both turtles disputing its purported key TSD role. Genes that may convert thermal inputs into sex-specific development (e.g., signaling and hormonal pathways, RNA-binding and heat-shock) were differentially regulated. Jak-Stat, Nf-κB, retinoic-acid, Wnt, and Mapk-signaling (not Akt and Ras-signaling) potentially mediate TSD thermosensitivity. Numerous species-specific ncRNAs (including Xist) were differentially-expressed, mostly upregulated at colder temperatures, as were unannotated loci that constitute novel TSD candidates. Cirbp showed warm-temperature upregulation in both turtles. Consistent transcription between turtles and alligator revealed putatively-critical reptilian TSD elements for male (Sf1, Amh, Amhr2) and female (Crabp2 and Hspb1) gonadogenesis. In conclusion, while preliminary, our data helps illuminate the regulation and evolution of vertebrate sex determination, and contribute genomic resources to guide further research into this fundamental biological process.

Efficient breathing at neonatal ages: A sex and Epo-dependent issue

During postnatal life, the respiratory control system undergoes intense development and is highly responsive to stimuli emerging from the environment. In fact, interruption of breathing prevents gas exchange and results in systemic hypoxia that, if prolonged, can lead to cardio-respiratory failure or sudden infant death. Moreover, in newborns and infants, respiratory disorders related to neural control dysfunction show significant sexual dimorphism with a higher prevalence in males. To this day, the therapeutic tools available to alleviate these respiratory disorders remain limited. Furthermore, the factors explaining the sexual dimorphism in newborns and during infancy remain unknown. Erythropoietin (Epo) was originally discovered as a cytokine able to increase the production of red blood cells upon conditions of reduced oxygen availability. We now know that Epo is a cytokine also secreted by neurons and astrocytes that protects the brain during trauma or hypoxic stress in a sex dependent manner. In this novel line of research, our previous studies demonstrated at adult ages that cerebral Epo acts as a respiratory stimulant in rodents and humans. These results provided a strong rationale for exploring the role of cerebral Epo in neuronal respiratory control during postnatal development. The objective of this review is to summarize our recent findings showing that cerebral Epo is a potent sex-specific respiratory stimulant at neonatal ages. Keeping in mind that Epo is routinely and safely administrated in newborn humans for anemia and neonatal asphyxia, we predict that our research provides the basis necessary to promote the clinical use of Epo against neonatal respiratory disorders related to neural control dysfunction.

Primary cilia in the developing pig testis

In vertebrates, a variety of cell types generate a primary cilium. Cilia are implicated in determination and differentiation of a wide variety of organs and during embryonic development. However, there is little information on the presence or function of primary cilia in the mammalian testis. Therefore, the objective of this study was to characterize expression of primary cilia in the developing pig testis. Testicular tissue from pigs at 2-10 weeks of age was analyzed for primary cilia by immunocytochemistry. Expression of primary cilia was also analyzed in testicular tissue formed de novo from a single cell suspension ectopically grafted into a mouse host. Functionality of primary cilia was monitored based on cilia elongation after exposure to lithium. Analysis showed that the primary cilium is present in testis cords as well as in the interstitium of the developing pig testis. Germ cells did not express primary cilia. However, we identified Sertoli cells as one of the somatic cell types that produce a primary cilium within the developing testis. Primary cilium expression was reduced from the second to the third week of pig testis development in situ and during de novo morphogenesis of testis tissue from a single cell suspension after xenotransplantation. In vitro, primary cilia were elongated in response to lithium treatment. These results indicate that primary cilia on Sertoli cells may function during testicular development. De novo morphogenesis of testis tissue from single cell suspensions may provide an accessible platform to study and manipulate expression and function of primary cilia.

Human exposure to endocrine disrupters and semen quality

Reproductive pathology in the male represents about 20% of infertility cases. Male infertility may be attributed to a number of causes, including genetic and congenital abnormalities, infection, multisystemic diseases, varicocele, and others; however, a significant number of cases are idiopathic. Global declines in semen quality were suggested to be associated with enhanced exposure to environmental chemicals that act as endocrine disrupters as a result of our increased use of pesticides, plastics, and other anthropogenic materials. A significant body of toxicology data based upon laboratory and wildlife animals studies suggests that exposure to certain endocrine disrupters is associated with reproductive toxicity, including (1) abnormalities of the male reproductive tract (cryptorchidism, hypospadias), (2) reduced semen quality, and (3) impaired fertility in the adult. There is, however, a relative paucity of studies designed to measure exposure to endocrine disrupters on semen quality parameters (sperm concentration, motility, morphology). An overview of the human semen quality literature is presented that examines the role of endocrine disrupters including organochlorines (OC), dioxins, phthalates, phytoestrogens, and chemical mixtures (pesticides and tobacco smoke).

Anti-Müllerian hormone levels in serum from human foetuses and children: pattern and clinical interest

Serum anti-Müllerian hormone (AMH) determination has been used to investigate gonadal development and abnormal sexual differentiation, but until recently, it was based on assays developed by specialized laboratories. A short time ago, a sensitive assay kit was developed commercially (Immunotech-Beckman Coulter) for clinical use. With this method, we established usual levels of serum AMH in fetuses, newborns, and pre-pubertal children, and evaluated the clinical value of this assay. AMH measurement required only 25 microl of sample and could be performed within 3 h. In females, AMH emerged after birth at low levels (median: 4 ng/ml). In males, AMH levels remained stable during fetal life (median: 44.4 ng/ml), peaked in the first months of life to reach a median of 124.7 ng/ml, then fell with wide individual variations. Cord blood AMH levels at birth may be useful to investigate ambiguous genitalia suspected prenatally. In children with isolated microphallus or hypospadias, decreased AMH values are in favor of testis dysfunction. When testes cannot be palpated, a single determination of serum AMH levels can distinguish between anorchia and cryptorchidism.

Connexin43 is expressed in mouse fetal ovary

Developmental studies have shown that connexin43 (Cx43) is expressed in the ovary from the first day of life and throughout the rest of postnatal development. In both mouse embryonic ovaries and testes, target-directed deletion of Cx43 gene induces a significant decrease in germinal cells, but the exact mechanism determining this reduction remains unknown. Moreover, recently we found that Cx43 is abundantly expressed in mouse testes from the earliest stages of its fetal development. In the present work we investigate whether Cx43 transcript and protein are expressed in mouse embryonic ovaries. Total RNA was analyzed with specific Cx43 oligonucleotides in RT-PCR studies. A Cx43 PCR product was detected in ovaries at 16.5 and 18.5 days postcoitum (dpc). Bands of 43-45 kDa, characteristic of Cx43, were detected in immunoblots of total homogenates of ovaries at 14.5 and 18.5 dpc. Cell type-specific expression of Cx43 was investigated using double-labeled sections incubated with specific antibodies against Cx43 and the enzyme 3beta-hydroxysteroid dehydrogenase (3betaHSD) or a germ cell nuclear antigen (GCNA1), which are cell markers of steroidogenic and germinal cells, respectively. At 18.5 dpc, Cx43 was found in conglomerates of 3betaHSD-positive cells. Cx43 was also localized at homocellular junctions between parenchyma pregranulosa cells, and at heterocellular junctions between pregranulosa and germinal cells. At these two latter localizations, Cx43 was traced back to 12.5 dpc. In conclusion, this study demonstrates for the first time that from the earliest stages of embryonic ovary development, Cx43 is expressed in principal cell types involved in control of female fertility. These data suggest that the gap junctions formed with Cx43 between somatic and germinal cells may be necessary for prenatal expansion of germinal cells at initial stages of fetal gonadal development.

The biosocial female choice theory of social stratification

For decades, the study of social stratification has been dominated by environmental theories. Herein a theory is proposed that contains both biological and sociocultural elements. The theory asserts that most human females, like females of many other mammalian species, have evolved mating preferences biased toward males who are competent in provisioning resources. This female bias is hypothesized to have been naturally selected because females with these biases nearly always have had a reproductive edge over females who lack such a bias. One result of this bias is that human females preferentially mate with males who strive to rise in social status. This, in turn, has favored males who attain or at least strive for high social status, and who advertise and even exaggerate whatever status they already have achieved. At the genetic level, the theory postulates that alleles have accumulated on the human genome that promote social status-striving and achievement to varying degrees. To account for why males are more prone toward status-striving than females, the theory contends that one or more genes on the Y-chromosome interact with genes on the remaining human chromosomes to incline males to gravitate toward social hierarchies and to strive for niches that are relatively high in those hierarchies. Both tested and untested hypotheses are derived from the theory and compared to the empirical evidence currently available.

Masculinized finger length patterns in human males and females with congenital adrenal hyperplasia

The ratio of the length of the second digit (2D) to the length of the fourth digit (4D) is greater in women than in men. Since androgens are involved in most somatic sex differences and since the sexual dimorphism in 2D:4D is stable from 2 years of age in humans, it was hypothesized that finger length pattern development might be affected by early androgen exposure. Human females with congenital adrenal hyperplasia (CAH) are exposed prenatally to higher than normal levels of adrenal androgens, providing an opportunity to test the effects of early androgen exposure on digit ratios. The 2D:4D was calculated for females with CAH, females without CAH, males with CAH, and males without CAH. Females with CAH had a significantly smaller 2D:4D on the right hand than did females without CAH. Males with CAH had a significantly smaller 2D:4D on the left hand than did males without CAH. A subset of six males with CAH had a significantly smaller 2D:4D on both hands compared with their male relatives without CAH. These results are consistent with the idea that prenatal androgen exposure reduces the 2D:4D and plays a role in the establishment of the sex difference in human finger length patterns. Finger lengths may therefore offer a retrospective marker of perinatal androgen exposure in humans.

Cognitive and behavioral characteristics of turner syndrome: exploring a role for ovarian hormones in female sexual differentiation

To better understand factors contributing to behavioral development, we studied patients with Turner syndrome (TS), a disorder typically marked by prenatal onset of ovarian dysfunction. We compared girls and women (ages 12 and up) with TS (n = 21) to matched controls (n = 21) in cognitive and motor skills, as well as sex-typed personality characteristics and activity preferences. Measures were categorized (based on prior studies) as showing an average male advantage (male-superior measures), female advantage (female-superior measures), or no sex difference (sex-neutral measures). It was hypothesized that, if gonadal function contributes to behavioral development, effects of this deficiency would be more prominent on sexually differentiated than sex-neutral measures and thus that patient-control differences would be most marked for measures that show sex differences. Our findings indicated that TS patients and controls differed more on cognitive and motor domains that show sex differences than on sex-neutral domains. Patients also had more "undifferentiated" personalities and showed reduced sex-typed interests and activities. Differing experiences, as indexed by interests and activities, did not explain the observed cognitive and motor differences. These results are consistent with a role for ovarian hormones acting on the brain to influence cognitive and behavioral development, although they do not rule out other possible interpretations.

Estrogen and spermatogenesis

Although it has been known for many years that estrogen administration has deleterious effects on male fertility, data from transgenic mice deficient in estrogen receptors or aromatase point to an essential physiological role for estrogen in male fertility. This review summarizes the current knowledge on the localization of estrogen receptors and aromatase in the testis in an effort to understand the likely sites of estrogen action. The review also discusses the many studies that have used models employing the administration of estrogenic substances to show that male fertility is responsive to estrogen, thus providing a mechanism by which inappropriate exposure to estrogenic substances may cause adverse effects on spermatogenesis and male fertility. The reproductive phenotypes of mice deficient in estrogen receptors alpha and/or beta and aromatase are also compared to evaluate the physiological role of estrogen in male fertility. The review focuses on the effects of estrogen administration or deprivation, primarily in rodents, on the hypothalamo-pituitary-testis axis, testicular function (including Leydig cell, Sertoli cell, and germ cell development and function), and in the development and function of the efferent ductules and epididymis. The requirement for estrogen in normal male sexual behavior is also reviewed, along with the somewhat limited data on the fertility of men who lack either the capacity to produce or respond to estrogen. This review highlights the ability of exogenous estrogen exposure to perturb spermatogenesis and male fertility, as well as the emerging physiological role of estrogens in male fertility, suggesting that, in this local context, estrogenic substances should also be considered "male hormones."