Morphological study for understanding the sexual pattern in ghost shrimp Callichirus major (Crustacea: Axiidea)

Callichirus major is a species of ghost shrimp that has burrowing habits, building underground galleries in the intertidal region of beaches. This study aimed to analyse some morphological parameters to verify its type of sexual pattern. A sample of 79 individuals, collected at the beach of Corujão, Espírito Santo, Brazil, was used. Data on the external morphology, presence of gonopores, carapace length (CL) and cheliped lengths (Lch) were obtained. In addition, the gonads were processed for histological analysis. The animals were divided into three categories: A, individuals with male characteristics; B, those presenting exclusively female characteristics; C, animals with characteristics of intersex, which presented supernumerary gonopores. Positive allometries were found for Lch versus CL only for category A, characterizing the group's marked heterochely. Histologically, it was possible to observe the presence of oocytes in category A and one case of male tissue in an intersex individual (category C). However, no genital ducts of both sexes were found in that individual. Callichirus major presents controversial sexual characters, which makes it difficult to understand the reproductive parameters and sexual pattern. However, maybe that species can develop a sexual system of hermaphroditism.     

Studies of gonadal sex differentiation

Gonadal differentiation has a determinative influence on sex development in human embryos. Disorders of sexual development (DSD) have been associated with persistent embryonal differentiation stages. Between 1998 and 2015, 139 female patients with various (DSD) underwent operations at the Scientific Center of Obstetrics, Gynaecology and Perynatology in Moscow, Russia. Clinical investigations included karyotyping, ultrasound imaging, hormonal measurement and investigations of gonadal morphology. The male characteristics in the embryo are imposed by testicular hormones. When these are absent or inactive, the fetus may be arrested at between developmental stages, or stay on indifferent stage and become phenotypically female. A systematic analysis of gonadal morphology in DSD patients and a literature review revealed some controversies and led us to formulate a new hypothesis about sex differentiation. Proliferation of the mesonephric system (tubules and corpuscles) in the gonads stimulates the masculinization of gonads to testis. Sustentacular Sertoli cells of the testes are derived from mesonephric excretory tubules, while interstitial Leydig cells are derived from the original mesenchyme of the mesonephros. According of the new hypothesis, the original mesonephric cells (tubules and corpuscles) potentially persist in the ovarian parenchyma. In female gonads, some mesonephric excretory tubules regress and lose the tubular structure, but form ovarian theca interna and externa, becoming analogous to the sustentacular Sertoli cells in the testis. The ovarian interstitial Leydig cells are derived from intertubal mesenchyme of the mesonephros, similar to what occurs in male gonads (testis). Surprisingly, the leading determinative factor in sexual differentiation of the gonads is the mesonephros, represented by the embryonic urinary system.     

Systematization of ambiguous genitalia

Sex assignment in newborns depends on the anatomy of the external genitalia, despite this stage being the final in embryogenesis. According to the current view, the genital tubercle is the embryonic precursor of penis and clitoris. It originates from mesenchymal tissue, but mesenchymal cells are arranged across the embryonal body and do not have specific androgen receptors. The nature of the signal that initiates early derivation of the indifferent genital tubercle is unknown at present. The aims of this article are to improve surgical management of intersex disorders and investigate the development of the genital tubercle. Clinical examination of 114 females with various forms of DSD revealed ambiguous (bisexual) external genitalia in 73 patients, and 51 of them underwent feminizing surgery. Intersexuality (ambiguity) in 46,XY patients results from disruptors in the pathways of sex steroid hormones or receptors; in 46,XX females arises from excessive levels of androgens. Systematization of intersex disorders distinguishes the karyotype, gonadal morphology, and genital anatomy to provide a differential diagnosis and guide appropriate surgical management. Modified feminizing clitoroplasty with preservation of the dorsal and ventral neurovascular bundles to retain erogenous sensitivity was performed in females with severe virilization (Prader degree III-V). The outgrowth of the genital tubercle and the fusion of the urethral fold proceed in an ordered fashion; but in some cases of ambiguity, there was discordance due to different pathways. Speculation about the derivation of the genital tubercle have discussed with a literature review. The genital tubercle derives from the following 3 layers: the ectodermal glans of the tubercle, the mesodermal corpora cavernosa and the endodermal urogenital groove. According to the new hypothesis, during the indifferent stages, the 5 sacral somites have to recede from their segmentation and disintegrate: the sclerotomes form the pelvic bones, the fused myotomes follow with their genuine neurotomes and the angiotomes join to the corpora cavernosa of the genital tubercle. Sexual differentiation of external genitalia is final in gender embryogenesis, but surprisingly derivation of the indifferent genital tubercle from 5 somites occurs before gonadal and internal organs development.     

Sexual differentiation and juvenile intersexuality in the European sea bass (Dicentrarchus labrax)

Sexual differentiation was studied at the histological level using a mixture of 30 families of sea bass Dicentrarchus labrax . Most of the fish (93%) differentiated into males as usually observed in farmed populations. All testes were differentiated when the males reached 12 cm and no more undifferentiated fish were found from 419 days post-fertilization (p.f.). In 28% of the males, among the biggest, sexual differentiation had already begun at 168 days p.f. (8.3–9.5 cm) and these fish started spermatogenesis in their first year of life. The other males differentiated later and remained immature at the end of their first year of life. Ovaries could be identified at the histological level from the age of 168 days p.f. (7.9–9.0 cm) and the females became significantly longer than the males from the age of 191 days p.f., i.e. during the process of ovarian differentiation. In the studied group, 62% of the males developed intratesticular oocytes. Such intersexuality had no consequence on growth rate. Intratesticular oocytes were also recorded in testes of wild males originating from Atlantic (Britain and Gulf of Gascogne) and West Mediterranean showing that juvenile intersexuality is not restricted to farmed populations but is a widespread phenomenon in sea bass.     

A case of intersexuality in pigs associated with a de novo paracentric inversion 9 (p1.2; p2.2)

In several mammalian species, genetic defects can be responsible for the interruption of and/or the deviation from the sequential steps of normal gonadal differentiation, leading to a sex-reversal syndrome. In pigs, female-to-male sex-reversal conditions are particularly frequent, but their aetiologies remain unclear. Chromosomal abnormalities that co-occur with sex-reversal disorders can be useful in the identification of loci containing responsible or susceptibility genes. This report describes a female-to-male SRY-negative intersex pig with a de novo paracentric inversion of the short arm of one chromosome 9 (p1.2; p2.2). We have fine mapped the proximal chromosomal breakpoint of this rearrangement because it corresponded to a region potentially involved in the pig intersexuality. Fluorescent in situ hybridization (FISH) experiments carried out with Bacterial Artificial Chromosome (BAC) clones located within the critical region defined by genetic linkage analysis and ordered on the porcine RH map allowed us to locate the proximal breakpoint between markers SW2571 and SW539. Further investigations are currently in progress to find new markers inside this interval, in order to determine the BAC in which the break occurred.     

THE EFFECTS OF TEMPERATURE ON SEXUAL DIFFERENTIATION IN THE TEMPERATURE SENSITIVE THELYGENIC—INTERSEXUAL OFFSPRING OF ORCHESTIA GAMMARELLUS (PALLAS) (AMPHIDOPA; CRUSTACEA

An increase in temperature to 25 or 30°C during embryonic development and the first stages of post-embryonic development in the temperature-sensitive thelygenic offspring of Orchestia gammarellus, brings about a higher male ratio in the broods, that is to say weakens or cancels the action of the feminising factor. The effect appears much earlier at 30 than at 25°C. At 30°C, the results achieved partly depend on the stage of embryonic development during which the heat treatment is applied. The more sensitive stages correspond to gastrulation and the formation of germ layers. The sensitivity to the increased temperature depends on the sexual genotype of the individuals: the 2AYY are more sensitive than the XY animals.     

Intersexuality in the amphipod Gammarus duebeni results from incomplete feminisation by the vertically transmitted parasitic sex ratio distorter Nosema granulosis

We investigated the effects of parasitism and temperature on the production of intersexes in the amphipod Gammarus duebeni from a field population at Cumbrae, Scotland. There was significant temporal variation in intersex frequency which ranged from 0.5 to 5.2% in monthly field collections. Prevalence of Nosema granulosis, a feminising microsporidian parasite, also varied temporally and there was a significant correlation between parasite prevalence and intersex frequency in the field. Intersexes (16.3 ± 0.4 mg) were larger than true females (14.8 ± 0.1 mg) but produced fewer eggs thus demonstrating a cost of intersexuality. Intersexes were less likely to be paired than true females. In a breeding experiment, only females infected by N. granulosis produced intersex offspring. Temperature had no effect on intersex frequency. Intersexes therefore appear to be the result of incomplete feminisation by N. granulosis in this population. These results contrast with previous studies of G. duebeni from different populations which found that intersexes were the result of abnormal development under environmental sex determination. We suggest that intersexuality may be induced by both environmental and parasitic factors in populations of G. duebeni. This revised version was published online in August 2006 with corrections to the Cover Date.     

The reproductive biology of Scyliorhinus canicula in the Bristol Channel, U.K.

Among 972 Scyliorhinus canicula , the overall sex ratio (males:females) was 1:1·23. Males matured between 490 and 540 mm L _T with 50% maturity at 520 mm. Females matured between 520 and 640 mm L _T with 50% maturity at 550 mm. Female gonadosomatic index peaked in May. Fecundity increased with fish length. The egg laying season lasted 10 months with a peak in June and July. The importance of erect, sessile invertebrates such as bryozoans, poriferans and hydroids as egg-case deposition sites has been established. Recently hatched fish were born in an equal sex ratio and at a mean length of 100·5 mm and mean weight of 3·07 g. One intersexual fish is described.     

Deep sequencing of a candidate region harboring the SOX9 gene for the canine XX disorder of sex development

A disorder of sex development (DSD) in dogs with female sex chromosomes (78, XX), a lack of the SRY gene and the presence of testes or ovotestes is commonly diagnosed in numerous breeds. The molecular background of DSD is not fully recognized but has been linked to the copy number variation in the region harboring the SOX9 gene. We applied a genome‐wide association study and targeted next‐generation sequencing techniques to compare DSD and normal female dogs. The genome‐wide association study did not indicate a significant chromosome region. Targeted next‐generation sequencing of a 1.5‐Mb region on canine chromosome 9 harboring the SOX9 gene revealed two putatively DSD‐associated copy number variations 355 kb upstream and 691 kb downstream of SOX9, four blocks of low polymorphism and two blocks of an elevated heterozygosity. An initial next‐generation sequencing analysis showed an association with two SNPs, but validation in larger cohorts did not confirm this result. We identified a large homologous fragment (over 243.8 kb), named hfMAGI2, located upstream of SOX9, that overlaps a known copy number variation region. It shows a high sequence similarity with the 5′ flanking region of the MAGI2 gene located on canine chromosome 18 that encodes a protein involved in ovary formation during early embryonic development. Our study showed that the identified copy number variation region located upstream of the SOX9 gene contains potential regulatory sequences (long non‐coding RNA and hfMAGI2) and led to the assumption that a multiplication of this element may alter expression of the SOX9 gene, triggering the DSD phenotype.