Linkage to CFA29 Detected in a Genome-Wide Linkage Screen of a Canine Pedigree Segregating Sry-Negative XX Sex Reversal

A comprehensive study of disorder of sex development in Staffordshire bull terrier dog

An 8-month-old female Staffordshire bull terrier was clinically examined because of external sexual organs abnormality-clitoral hypertrophy. As stated by the owner, the female dog had not been in heat yet. Serum profile of testosterone (3.39 ng/ml), as well as an anti-Műllerian hormone (24.0 ng/ml), suggested the presence of testicular tissue. On the contrary, the estimated level of 17β-oestradiol (24.6 pg/ml) was approximately two times higher when compared with the normal anoestrus values (5-10 pg/ml). A midline laparotomy was performed to detect the cranial parts of the genital system. Gonads resembling testicle or ovotestis (left) and hypoplastic testicle (right) was visible. Cranial portion of gonads was attached to structures indicative of bilateral epididymidis. The next tubular structures-oviducts were resected along with adherent parts of a hypoplastic uterus. Histological evaluation confirmed that the examined gonad samples were testicles with modified interstitial testicular tissue. Hypertrophy of interstitial space was predominantly formed by Leydig cells. Examination of a cross-section through the head of suspected epididymidis confirmed their characteristic structures. In addition, the characteristic configuration of the oviducts was presented. The uterus consisted of three walls, in which the endometrium was hypoplastic with the presence of endometrial glands. No Y chromosome was detected by chromosomal analysis using CFA Y probe and the amplification of SRY-gene coding region (813 bp) indicated genotype 78, XX; SRY-negative. Sequencing of SOX9 gene exons 1-3 did not reveal any differences in exon 1 and 3. On the contrary, a few changes were determined in the SOX9 exon 2 sequences: G instead of A at position 103; C instead of reference T at position 115; GCG instead of reference CGC at position 138-140; T instead of reference C at positions 161, 164 and 167.

XX Disorder of Sex Development is associated with an insertion on chromosome 9 and downregulation of RSPO1 in dogs (Canis lupus familiaris)

Remarkable progress has been achieved in understanding the mechanisms controlling sex determination, yet the cause for many Disorders of Sex Development (DSD) remains unknown. Of particular interest is a rare XX DSD subtype in which individuals are negative for SRY, the testis determining factor on the Y chromosome, yet develop testes or ovotestes, and both of these phenotypes occur in the same family. This is a naturally occurring disorder in humans (Homo sapiens) and dogs (C. familiaris). Phenotypes in the canine XX DSD model are strikingly similar to those of the human XX DSD subtype. The purposes of this study were to identify 1) a variant associated with XX DSD in the canine model and 2) gene expression alterations in canine embryonic gonads that could be informative to causation. Using a genome wide association study (GWAS) and whole genome sequencing (WGS), we identified a variant on C. familiaris autosome 9 (CFA9) that is associated with XX DSD in the canine model and in affected purebred dogs. This is the first marker identified for inherited canine XX DSD. It lies upstream of SOX9 within the canine ortholog for the human disorder, which resides on 17q24. Inheritance of this variant indicates that XX DSD is a complex trait in which breed genetic background affects penetrance. Furthermore, the homozygous variant genotype is associated with embryonic lethality in at least one breed. Our analysis of gene expression studies (RNA-seq and PRO-seq) in embryonic gonads at risk of XX DSD from the canine model identified significant RSPO1 downregulation in comparison to XX controls, without significant upregulation of SOX9 or other known testis pathway genes. Based on these data, a novel mechanism is proposed in which molecular lesions acting upstream of RSPO1 induce epigenomic gonadal mosaicism.

Sex Reversal in Non-Human Placental Mammals

Gonads are very peculiar organs given their bipotential competence. Indeed, early differentiating genital ridges evolve into either of 2 very distinct organs: the testis or the ovary. Accumulating evidence now demonstrates that both genetic pathways must repress the other in order for the organs to differentiate properly, meaning that if this repression is disrupted or attenuated, the other pathway may completely or partially be expressed, leading to disorders of sex development. Among these disorders are the cases of XY male-to-female and XX female-to-male sex reversals as well as true hermaphrodites, in which there is a discrepancy between the chromosomal and gonadal sex. Here, we review known cases of XY and XX sex reversals described in mammals, focusing mostly on domestic animals where sex reversal pathologies occur and on wild species in which deviations from the usual XX/XY system have been documented.

Sox9 duplications are a relevant cause of Sry-negative XX sex reversal dogs

Sexual development in mammals is based on a complicated and delicate network of genes and hormones that have to collaborate in a precise manner. The dark side of this pathway is represented by pathological conditions, wherein sexual development does not occur properly either in the XX and the XY background. Among them a conundrum is represented by the XX individuals with at least a partial testis differentiation even in absence of SRY. This particular condition is present in various mammals including the dog. Seven dogs characterized by XX karyotype, absence of SRY gene, and testicular tissue development were analysed by Array-CGH. In two cases the array-CGH analysis detected an interstitial heterozygous duplication of chromosome 9. The duplication contained the SOX9 coding region. In this work we provide for the first time a causative mutation for the XXSR condition in the dog. Moreover this report supports the idea that the dog represents a good animal model for the study of XXSR condition caused by abnormalities in the SOX9 locus.

A lack of association between polymorphisms of three positional candidate genes (CLASP2 , UBP1, and FBXL2) and canine disorder of sexual development (78,XX; SRY -negative)

A disorder of sexual development (DSD) of dogs with a female karyotype, missing SRY gene, and presence of testicles or ovotestes is quite commonly diagnosed. It is suggested that this disorder is caused by an autosomal recessive mutation; however, other models of inheritance have not been definitely ruled out. In an earlier study it was hypothesized that the mutation may reside in a pericentromeric region of canine chromosome 23 (CFA23). Three positional candidate genes (CLASP2, UBP1, and FBXL2) were selected in silico in the search for polymorphisms in 7 testicular or ovotesticular XX DSD dogs, 8 XX DSD dogs of unknown cause (SRY-negative, with enlarged clitoris and unknown histology of gonads), and 29 normal female dogs as a control group. Among the 15 molecularly studied dogs with enlarged clitoris there were 3 new cases of testicular or ovotesticular XX DSD and 4 new cases of XX DSD with unknown cause (histology of the gonads unknown). Altogether, 11 (including 10 novel) polymorphisms in 5'- and 3'-flanking regions of the studied genes were found. The distribution analysis of these polymorphisms showed no association with the DSD phenotypes. Thus, it was concluded that the presence of the causative mutation for testicular or ovotesticular XX DSD in the pericentromeric region of CFA23 is unlikely.

Dog as a model in studies on human hereditary diseases and their gene therapy

During the last 15 years spectacular progress has been achieved in knowledge on the dog genome organization and the molecular background of hereditary diseases in this species. A majority of canine genetic diseases have their counterparts in humans and thus dogs are considered as a very important large animal model in human biomedicine. Among canine monogenic diseases with known causative gene mutations there are two large groups classified as retinal dystrophies and lysosomal storage diseases. Specific types of these diseases are usually diagnosed in a single or several breeds. A well known disorder, restricted to a single breed, is congenital stationary night blindness described in Briards. This disease is a counterpart of Leber amaurosis in children. On the other hand, one of the most common monogenic human diseases (Duchenne muscular dystrophy), has its canine counterparts in several breeds (e.g., the Golden retriever, Beagle and German short-haired pointer). For some of the canine diseases gene therapy strategy was successfully applied, e.g., for congenital stationary night blindness, rod-cone dystrophy and muccopolysaccharydoses type I, IIIB and VII. Since phenotypic variability between the breeds is exceptionally high, the dog is an interesting model to study the molecular background of congenital malformations (e.g., dwarfism and osteoporosis imperfecta). Also disorders of sexual development (DSD), especially testicular or ovotesticular DSD (78,XX; SRY-negative), which is widely distributed across dozens of breeds, are of particular interest. Studies on the genetic background of canine cancers, a major health problem in this species, are also quite advanced. On the other hand, genetic studies on canine counterparts of major human complex diseases (e.g., obesity, the metabolic syndrome and diabetes mellitus) are still in their infancy.

Natural exceptions to normal gonad development in mammals

Gonads are the only organs with 2 possible developmental pathways, testis or ovary. A consequence of this unique feature is that mutations in genes controlling gonad development give rise not only to gonadal malformation or dysfunction but also to frequent cases of sex reversal, including XY females, XX males and intersexes. Most of our current knowledge on mammalian sex determination, the genetic process by which the gonadal primordia are committed to differentiate as either testes or ovaries, has derived mainly from the study of sex-reversed mice obtained by direct genetic manipulation. However, there are also numerous cases of natural exceptions to normal gonad development which have been described in a variety of mammals, including both domestic and wild species. Here, we review the most relevant cases of: (1) natural, non-induced sex reversal and intersexuality described in laboratory rodents, including Sxr and B6-Y(DOM) mice; (2) sex reversal in domestic animals, including freemartinism in bovids and pigs, XX sex reversal in pigs, goats and dogs, XY sex reversal in the horse, and sex chromosome chimerism and sex reversal in the cat, and (3) sex reversal in wild mammals, including the generalised true hermaphroditism described in talpid moles, XY sex reversal in Akodon, Microtus and Dicrostonyx species, males lacking a Y chromosome and SRY in Ellobius lutescens, the X* chromosome of Myopus schisticolor, and sex chromosome mosaicism and X0 females in Microtus oregoni. These studies are necessary to elucidate particular aspects of mammalian gonad development in some instances and to understand how the genetic mechanisms controlling gonad development have evolved.

Gonadal and sex differentiation abnormalities of dogs and cats

The molecular steps in normal sexual development were largely discovered by studying patients and animal models with disorders of sexual development (DSD). Although several types of DSD have been reported in the cat and dog, which are often strikingly similar to human DSD, these have been infrequently utilized to contribute to our knowledge of mammalian sexual development. Canine and feline cases of DSD with sufficient evidence to be considered as potential models are summarized in this report. The consensus DSD terminology, and reference to previous terminology, is used to foster adoption of a common nomenclature that will facilitate communication and collaboration between veterinarians, physicians, and researchers. To efficiently utilize these unique resources as molecular tools continue to improve, it will be helpful to deposit samples from valuable cases into repositories where they are available to contribute to our understanding of sexual development, and thus improve human and animal health.

Sexual dimorphism in mouse metanephroi exposed to 17 beta-estradiol in vitro

17beta-Estradiol, the most potent circulating estrogen, has been shown to greatly impact on the development and formation of tissues of the urogenital tract. The adult kidney has previously been shown to be highly responsive to 17beta-estradiol stimulation. However, the direct effect of 17beta-estradiol on kidney development remains unclear.

AIM

To investigate the direct effect of 17beta-estradiol on male and female metanephric kidney development.

METHODS

Whole embryonic-day-12.5 (E12.5) C57Bl/6 male and female mouse metanephroi were cultured in the presence of varying concentrations of 17beta-estradiol (0.1-5.0 nM) for 72 h. Metanephric development was assessed using immunofluorescence labeling techniques. The real-time polymerase chain reaction was used to investigate estrogen receptor-alpha (ERalpha), glial-cell-line-derived neurotrophic factor (GDNF) and its associated receptor cRET, transforming growth factor-beta (TGFbeta1), TGFbeta2 and TGFbeta3 mRNA expression levels.

RESULTS

ERalpha was present in developing metanephroi at E12.5; however, ERbeta was absent. No significant sex difference in ERalpha mRNA expression was observed. Significant increases in the number of ureteric branch points, terminal tips and developing glomeruli were observed in female metanephroi cultured in the presence of 1.0 and 5.0 nM 17beta-estradiol. Conversely, no significant effect was observed in male metanephroi cultured with 17beta-estradiol. GDNF and cRET mRNA expression was increased in both male and female metanephroi, whilst TGFbeta1 and TGFbeta2 mRNA expression was decreased following culture in the presence of 17beta-estradiol.

CONCLUSION

This study is the first to establish that the mouse metanephros displays a sexual dimorphism in response to specific concentrations of estrogens.