Effects of oestrogen treatment on testicular descent, inguinal closure and prostatic development in a male marsupial, Macropus eugenii

Inverse Correlation Between an Organ's Cancer Rate and Its Evolutionary Antiquity

Human cancer rates vary dramatically across the range of internal organs in the body, but there is no single model to explain the variation and there is also no obvious overall pattern to it. Theories have been proposed to account for high rates in particularly cancer-prone organs, and they usually concentrate on the peculiar vulnerability of certain cells to mutation (e.g., lung cells' direct exposure to airborne carcinogens). These explanations are valuable for understanding mechanisms of disease and also for cancer prevention, but they address neither the overall distribution of cancers nor the possibility that some states of differentiation may be intrinsically less stable than others to the effects of random mutation, a possibility predicted on purely theoretical grounds many years ago. This brief report describes an overall pattern to human organ-specific cancer incidence data and shows that organ-specific cancer rates correlate negatively with an organ's evolutionary antiquity. Although the relationship may just be coincidental, it suggests the possibility that recently-evolved differentiation states may be intricnsically more vulnerable to neoplastic change. Extrapolation of the regression line to a cancer incidence of zero equates to a level of tissue organization typical of 660 Myr ago; the inferred beginning of neoplasia therefore coincides with the rise of complex multicellular animals.

Oestrogen blocks the nuclear entry of SOX9 in the developing gonad of a marsupial mammal

Background

Hormones are critical for early gonadal development in nonmammalian vertebrates, and oestrogen is required for normal ovarian development. In contrast, mammals determine sex by the presence or absence of the SRY gene, and hormones are not thought to play a role in early gonadal development. Despite an XY sex-determining system in marsupial mammals, exposure to oestrogen can override SRY and induce ovarian development of XY gonads if administered early enough. Here we assess the effect of exogenous oestrogen on the molecular pathways of mammalian gonadal development.

Results

We examined the expression of key testicular (SRY, SOX9, AMH and FGF9) and ovarian (WNT4, RSPO1, FOXL2 and FST) markers during gonadal development in the marsupial tammar wallaby (Macropus eugenii) and used these data to determine the effect of oestrogen exposure on gonadal fate. During normal development, we observed male specific upregulation of AMH and SOX9 as in the mouse and human testis, but this upregulation was initiated before the peak in SRY expression and 4 days before testicular cord formation. Similarly, key genes for ovarian development in mouse and human were also upregulated during ovarian differentiation in the tammar. In particular, there was early sexually dimorphic expression of FOXL2 and WNT4, suggesting that these genes are key regulators of ovarian development in all therian mammals. We next examined the effect of exogenous oestrogen on the development of the mammalian XY gonad. Despite the presence of SRY, exogenous oestrogen blocked the key male transcription factor SOX9 from entering the nuclei of male somatic cells, preventing activation of the testicular pathway and permitting upregulation of key female genes, resulting in ovarian development of the XY gonad.

Conclusions

We have uncovered a mechanism by which oestrogen can regulate gonadal development through the nucleocytoplasmic shuttling of SOX9. This may represent an underlying ancestral mechanism by which oestrogen promotes ovarian development in the gonads of nonmammalian vertebrates. Furthermore, oestrogen may retain this function in adult female mammals to maintain granulosa cell fate in the differentiated ovary by suppressing nuclear translocation of the SOX9 protein.

See commentary: http://www.biomedcentral.com/1741-7007/8/110

AHR signaling in prostate growth, morphogenesis, and disease

Most evidence of aryl hydrocarbon receptor (AHR) signaling in prostate growth, morphogenesis, and disease stems from research using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to pharmacologically activate the AHR at various stages of development. This review discusses effects of TCDD on prostate morphogenesis and highlights interactions between AHR and other signaling pathways during normal and aberrant prostate growth. Although AHR signaling modulates estrogen and androgen signaling in other tissues, crosstalk between these steroid hormone receptors and AHR signaling cannot account for actions of TCDD on prostate morphogenesis. Instead, the AHR appears to act within a cooperative framework of developmental signals to regulate timing and patterning of prostate growth. Inappropriate activation of AHR signaling as a result of early life TCDD exposure disrupts the balance of these signals, impairs prostate morphogenesis, and has an imprinting effect on the developing prostate that predisposes to prostate disease in adulthood. Mechanisms of AHR signaling in prostate growth and disease are only beginning to be unraveled and recent studies have revealed its interactions with WNT5A, retinoic acid, fibroblast growth factor 10, and vascular endothelial growth factor signaling pathways.

Effects of growth factors on testicular morphogenesis

Since the discovery of the sex-determining gene Sry in 1990, research effort has focused on the events downstream of its expression. A range of different experimental approaches including gene expression, knocking-out and knocking-in genes of interest, and cell and tissue culture techniques have been applied, highlighting the importance of growth factors at all stages of testicular morphogenesis. Migration of primordial germ cells and the mesonephric precursors of peritubular myoid cells and endothelial cells to the gonad is under growth factor control. Proliferation of both germ cells and somatic cells within the gonadal primordium is also controlled by cytokines as is the interaction of Sertoli cells (with each other and with the extracellular matrix) to form testicular cords. Several growth factors/growth factor families (e.g., platelet-derived growth factor, fibroblast growth factor family, TGFbeta family, and neurotrophins) have emerged as key players, exerting an influence at different time points and steps in organogenesis. Although most evidence has emerged in the mouse, comparative studies are important in elucidating the variety, potential, and evolution of control mechanisms.

Genome-wide linkage analysis of inguinal hernia in pigs using affected sib pairs

BACKGROUND

Inguinal and scrotal hernias are of great concern to pig producers, and lead to poor animal welfare and severe economic loss. Selection against these conditions is highly preferable, but at this time no gene, Quantitative Trait Loci (QTL), or mode of inheritance has been identified in pigs or in any other species. Therefore, a complete genome scan was performed in order to identify genomic regions affecting inguinal and scrotal hernias in pigs. Records from seedstock breeding farms were collected. No clinical examinations were executed on the pigs and there was therefore no distinction between inguinal and scrotal hernias. The genome scan utilised affected sib pairs (ASP), and the data was analysed using both an ASP test based on Non-parametric Linkage (NPL) analysis, and a Transmission Disequilibrium Test (TDT).

RESULTS

Significant QTLs (p < 0.01) were detected on 8 out of 19 porcine chromosomes. The most promising QTLs, however, were detected in SSC1, SSC2, SSC5, SSC6, SSC15, SSC17 and SSCX; all of these regions showed either statistical significance with both statistical methods, or convincing significance with one of the methods. Haplotypes from these suggestive QTL regions were constructed and analysed with TDT. Of these, six different haplotypes were found to be differently transmitted (p < 0.01) to healthy and affected pigs. The most interesting result was one haplotype on SSC5 that was found to be transmitted to hernia pigs with four times higher frequency than to healthy pigs (p < 0.00005).

CONCLUSION

For the first time in any species, a genome scan has revealed suggestive QTLs for inguinal and scrotal hernias. While this study permitted the detection of chromosomal regions only, it is interesting to note that several promising candidate genes, including INSL3, MIS, and CGRP, are located within the highly significant QTL regions. Further studies are required in order to narrow down the suggestive QTL regions, investigate the candidate genes, and to confirm the suggestive QTLs in other populations. The haplotype associated with inguinal and scrotal hernias may help in achieving selection against the disorder.

Penile development is initiated in the tammar wallaby pouch young during the period when 5alpha-androstane-3alpha,17beta-diol is secreted by the testes

Virilization of the urogenital tract is under the control of testicular androgens in all mammals. In tammar young, prostate differentiation begins between d 20 and d 40 under the control of the testicular androgen 5alpha-androstane-3alpha,17beta-diol (5alpha-adiol), but uncertainties exist about the control of penile development. We performed longitudinal studies up to d 150 of pouch life to define normal penile development and the effects of androgen administration and castration. In control animals the male phallus was longer than the female phallus by d 48. Closure of the urethra in males begins around d 60 and continues to at least d 150. Administration of supraphysiological doses of testosterone to females caused penile development equivalent to that of the male and also induced partial closure of the urethral groove by d 150. Castration of male pouch young at d 25 prevented penile development, whereas the penis in males castrated at d 40, 80, or 120 had partial closure of the urethral groove. Administration of 5alpha-adiol to females from d 20-40 also caused partial closure of the urethral groove and some growth of the phallus at d 150, whereas 5alpha-adiol treatment from d 40-80 or 80-120 caused some penile growth but had little effect on urethral development. These findings, together with the fact that we found no sex differences in plasma levels of testosterone, dihydrotestosterone, 5alpha-adiol, dehydroepiandrosterone, or androstenedione from d 51-227, clearly indicate that the action of 5alpha-adiol between d 20 and 40 imprints later differentiation of the male penis.

The role of androgens in development of the scrotum of the grey short-tailed Brazilian opossum ( Monodelphis domestica)

In eutherian mammals, sex differentiation is initiated by expression of the testis-determining gene on the Y chromosome. Subsequent phenotypic development of the reproductive tract and genitalia depends on the production of hormones by the differentiated testis. In marsupials the mechanisms of phenotypic development may vary from this pattern, as differentiation of the scrotal primordia has been shown to occur before that of the gonad. Thus, the development of the scrotum in the marsupial has been regarded as an androgen-independent process. We have sought to clarify the ontogeny of scrotal development and the appearance of androgen receptor immunoreactivity by examining Monodelphis domesticaembryos/pups from 1 day prior to birth until 2 days after birth. We have also used immunocytochemistry to determine the expression of the key steroidogenic enzyme 3beta-hydroxysteroid dehydrogenase as an indicator of when the developing gonad may be capable of synthesizing androgens. Expression of this enzyme was first detected in the gonads and adrenals of both sexes 1 day prior to birth and before the appearance of scrotal bulges. Androgen receptor immunoreactivity was detected in the scrotal anlagen of male opossum pups as early as 1 day following birth. This finding is significantly earlier than previous reports and coincides with the appearance 1 day after birth of distinct scrotal bulges. Androgen receptor immunoreactivity was also observed in the genital tubercles of male pups, but not female pups, 2 days after birth. These results suggest that androgens may play an important role in the development of the male genitalia at a much earlier stage than that indicated by previously published work and that scrotal development in this species may not be androgen-independent.

The development of the gubernaculum and inguinal closure in the marsupial Macropus eugenii

This study reports the developmental anatomy of testicular descent and inguinal closure of the tammar wallaby (Macropus eugenii) from birth to maturity. In females the ovary migrated caudally between days 10 and 20 after birth. The gubernaculum differentiates into the round ligament in the abdomen and extra-abdominally as the ilio-marsupialis muscle of the mammary glands. In males the testes migrated to the internal inguinal ring by day 20 post partum (pp), coinciding with the enlargement of the gubernaculum, and from the internal inguinal ring to the scrotum between days 20 and 65 pp. During descent there was an increase in the hyaluronic acid concentration in cells of the gubernaculum and scrotum. Development of the cremaster muscle began by day 10 pp on the periphery of the gubernaculum and its basic structure was completed by day 60 pp. After descent the inguinal canal closed between days 50 and 60 pp, but a small irregular lumen persisted, somewhat similar to that seen in the congenital scrotal hydrocoele of humans. Tammars have a hopping mode of locomotion and, like humans, are essentially bipedal. We suggest that inguinal closure evolved in these two species because their upright posture may otherwise lead to a high incidence of inguinal hernias.