Cross-reactivity to mammalian anti-H-Y antiserum in teleostean fish

Molecular mechanisms of TSD in reptiles: a search for the magic bullet

Significant progress has been made in understanding mechanisms of genetic sex determination. The ZFY gene encodes a zinc finger protein but is not the primary signal in sex determination. The SRY gene is the testis determining gene in man, mouse, rabbit, and probably marsupial mouse and wallaby. Temperature dependent sex determination probably involves a modification of development of the indifferent gonad due to differential expression of one or more specific DNA sequences whose behavior is controlled by some temperature sensitive process or to differential action of a gene product such as a protein. There are ZFY and SRY-like genes in reptiles. We cloned and sequenced a portion of the ZFY gene (Zft) from snapping turtle (Chelydra serpentina) that is found in both sexes. We cloned and sequenced portions of SRY-like genes (Sra for SRY-related-autosomal) from snapping turtle. Similar genes are found in alligator (Alligator mississippiensis) and lizards. Cladistic analysis suggests that there are two or three major families of SRY-like genes in vertebrates in addition to sex specific SRY genes located on the Y chromosome of eutherian and marsupial mammals. When placed on a phylogenetic tree these data indicate that Sras were present in early tetrapods. Sequestering of the SRY gene on the Y chromosome probably happened only once and this may have been the defining moment that set the mammalian line of Therapsid reptiles apart from other reptilian groups.

On the evolution of sex determination

Female mice reject skin grafts from intrastrain males because of the H-Y transplantation antigen. Those females produce antibodies that recognize a male-specific cell-surface antigen in serological tests. The serological antigen has also been called 'H-Y', but there is evidence that the two antigens are distinct. We therefore refer to the transplantation antigen as H-Yt, or transplantation H-Y, and to the serological antigen as serological H-Y, or simply H-Y, without prejudice whether these are the same or related or separate antigens. In this study, sex-specific expression of serological H-Y antigen was found in 25 new vertebrate species representing each of seven major vertebrate classes. There was a strong correlation between expression of H-Y and occurrence of the heterogametic-type gonad, although unusual patterns of H-Y expression were noted in cases of temperature-influenced sex determination and in systems representing possible transition from one mode of heterogamety to the other. Male and female heterogamety are found side-by-side in certain freshwater toothed carps; and distinct sex chromosomes have been recognized in certain amphibians, even though they are not apparent in certain reptiles and primitive birds. In seven ophidian species, in which the female is the heterogametic sex, H-Y was detected in the female; and in three species of Ranidae in which the male is heterogametic, it was detected in the male. In three species of cartilaginous fish and in one of the cyclostomes, in which heterogamety has not been ascertained, H-Y was detected in the male, suggesting that those primitive fishes are male-heterogametic. Evidently, then, heterogamety and sex-chromosome heteromorphism are polyphyletic, although certain sex-determining genes may be held in common among the diverse taxonomic groups.

The occurrence of serological H-Y antigen (Sxs antigen) in the diandric protogynous wrasse, Coris julis (L.) (Labridae, Teleostei)

The serological sex-specific (Sxs) antigen (previously called 'H-Y antigen') has been shown, in various vertebrate species ranging from fish to mammals, to be characteristic of the heterogametic sex. We studied a protogynous hermaphrodite, Coris julis, in order to examine whether the change of a female to a secondary male also involves a change in the Sxs-antigen phenotype. The (homogametic) females of this species were found to be Sxs negative, while both primary and secondary males were Sxs positive. This was true not only for gonads but also for nongonadal tissues. The administration of androgen to females is known to cause sex inversion in this species; we were able to demonstrate this again at the histological level, and found that androgen results in a Sxs positive phenotype in all tissues studied (gonads, spleen, muscle). We propose that androgen is responsible, directly or indirectly, for the occurrence of the Sxs antigen.

An ovarian regression syndrome in the platyfish, Xiphophorus maculatus

The highly inbred Coatzacoalcos (Cp) strain of the platyfish, Xiphophorus maculatus, was noted for a high percentage of infertile females (XX). The ovaries of approximately one-quarter of all females regress. The time of gonadal atrophy varied from before sexual maturation up to 11 months of age. The gonadotropic zone of the pituitary was hypertrophied in regressed females. Transplants of immature testes and ovarian tissue into the caudal musculature of regressed females and the subsequent maturation of the grafts demonstrated that the ovarian degeneration was not due to pituitary or hypothalamic malfunction or an autoimmune disease. The cause of the gonadal degeneration was apparently localized to the ovary itself. This phenomenon was never observed in males (XY). Regressed ovaries fell into two categories, designated types I and II, with all being characterized by the presence of ductlike structures which resembled male efferent ducts, lined by Sertoli cells. Type I ovaries bore a marked similarity to certain mammalian dysgenetic gonads, while type II ovaries contained many proliferating germ cells and could be compared to the human neoplasm termed gonadoblastoma. It is suggested that the physiological lesion responsible for the ovarian regression syndrome involves the processes that control the determination and differentiation of the germ cells similar to those found in human 46,XY gonadal dysgenesis.

Monoclonal antibodies against spermatozoa of the common carp (Cyprinus carpio L.). I. A study germ cell antigens in adult males and females

Eleven monoclonal antibodies that recognize membrane determinants on spermatozoa of the carp Cyprinus carpio L. have been produced. Indirect immunofluorescence revealed that these determinants are uniformly distributed on the surface of head and midpiece. Most of them are also present on the outer membrane of precursor sperm cells. Although none of the monoclonal antibodies reacted with carp somatic tissue, five monoclonal antibodies were positive for surface membrane determinants of oogonia and early prophase oocytes in carp ovary. Preliminary analysis of the testis and ovary of three other species of fish showed that some carp determinants are shared with germ cells from Barbus conchonius, Clarias lazera, or Salmo gairdneri.

H-Y antigen in the chicken

To determine whether asymmetrical development of the chicken ovary could be related to differential expression or function of H-Y antigen, the putative ZW ovary inducer, we compared the ability of cells from the left and right gonad to absorb H-Y antibodies in 17-day chick embryos and in one-day-old hatchlings. In addition, we studied uptake of soluble H-Y antigen by gonadal cells in 17-day embryos, one-day-old hatchlings, and young adults. Indications are that H-Y is present in the left gonad of the female, and to a lesser extent in the right, and not in the testes of the male. Our preliminary results indicate moreover that the right ZW gonad may lack receptor sites for soluble H-Y at around the time of hatching. It may be inferred that expression of H-Y antigen is a prerequisite of ovarian development in birds, although it remains to be determined unambiguously whether H-Y is the primary inducer of the ZW gonad or an accessory molecule involved in some intermediate aspect of gonadal development.

H-Y antigen expression in temperature sex-reversed turtles (Emys orbicularis)

H-Y antigen has been used as a marker for the heterogametic sex and is assumed to be an organizing factor for the heterogametic gonad. In the turtle Emys orbicularis, H-Y antigen is restricted to the female cells, indicating a female heterogamety (ZZ/ZW) sex-determining mechanism. Moreover, the sexual differentiation of the gonads is temperature sensitive, and complete sex reversal can be obtained at will. In this framework the relationships between H-Y antigen, temperature, and gonadal phenotype were studied. Mouse H-Y antiserum was absorbed with blood and gonadal cells of control wild male and female adults, and with blood and gonadal cells from three lots of young turtles from eggs incubated at 25-26 degrees C (100% phenotypic males), at 30-30.5 degrees C (100% phenotypic females), or at 28.5-29 degrees C (majority of females with some males and intersexes). The residual activity of H-Y antiserum was then estimated using an immunobacterial rosette technique. In adults, both blood cells and gonadal cells were typed as H-Y negative in males and as H-Y positive in females. In each of the three lots of young, blood cells were H-Y negative in some individuals and H-Y positive in others. The proposed interpretation is that the H-Y negative individuals were genotypic males (ZZ) and the H-Y positive were genotypic females (ZW). The gonads of these animals were then pooled in different sets according to their sexual phenotype and to the presumed genotypic sex (i.e., blood H-Y phenotype). Testicular cells were typed as H-Y negative in genotypic males as well as in the presumed sex-reversed genotypic females; likewise, ovarian cells were typed as H-Y positive in genotypic females as well as in the presumed sex-reversed genotypic males. These results provide additional evidence that H-Y antigen expression is closely associated with ovarian structure in vertebrates displaying a ZZ/ZW sex-determining mechanism.

Mammalian cross-reactive H-Y antigen induces sex reversal in vitro in the avian testis

Testes of either newborn rats or newly hatched chickens, dissociated into single cell suspensions, reorganize in vitro into their histotypic structures. In birds, the heterogametic female sex is H-Y antigen positive, and not the male as in mammals. Cocultivation of rat and chicken testicular cells results in the reorganization of an ovotestis. A similar result is obtained after cultivation of chicken testicular cells in the supernatant medium of cultured human male Burkitt lymphoma Daudi cells. Rat testicular Sertoli cells as well as Daudi cells are a source of H-Y antigen. The simultaneous application of H-Y antigen and anti-H-Y antiserum prevents ovotestis formation. It is concluded that H-Y antigen which is known to be testis-organizing in mammals, is the ovary-organizing factor in birds.

H-Y antigen in transsexuality, and how to explain testis differentiation in H-Y antigen-negative males and ovary differentiation in H-Y antigen-positive females

H-Y antigen was determined in eight transsexual patients. Two of the four male-to-female transsexual patients typed as H-Y antigen-negative, while the other two typed as expected from their phenotypic and gonadal sex, namely H-Y antigen-positive. Of the four female-to-male transsexual patients, three typed as H-Y antigen-positive and one was H-Y antigen-negative, as expected. The presence of normal testes in H-Y antigen-negative males is assumed to result from a mutation of nucleotide sequences of the H-Y structural gene for antigenic determinants. Thus, an H-Y is produced with normal receptor-binding activity which can sustain the testis determination of the bipotent gonadal anlage. In the case of H-Y antigen-positive females with normal ovaries a deletion of the autosomally located H-Y structural gene is assumed. This deletion should affect sequences for repressor-binding (as was suggested for H-Y antigen-positive XX-males) and for receptor-binding activity of the H-Y antigen molecule. The resulting H-Y antigen is unable to bind to the gonadal receptor of the bipotent gonadal anlage. Thus an ovary is determined. The relevance of H-Y antigen for the aetiology of transsexualism is discussed.

Does H-Y antigen induce the heterogametic ovary?

To determine whether phylogenetically conservative H-Y antigen plays any part in gonadal differentiation among the nonmammalian vertebrates, we studied expression and binding of H-Y in the frog, Xenopus laevis. Soluble H-Y obtained from mouse testis and soluble H-W from chicken ovary bound specifically to cells of the ZZ testis from normal Xenopus males. In addition, H-Y (H-W) appeared selectively in the ovaries of ZZ genetic males that had been induced to become functional females by exposure to estradiol. Our observations suggest that H-Y (H-W) antigen may be involved in differentiation of the ZW ovary, and also that synthesis of H-Y may be regulated by sex steroids in the primitive ZW/ZZ species.

Induction of H-Y antigen in the gonads of male quail embryos by diethylstilbestrol

In quails, H-Y antigen is induced by oestrogens in the gonads of the originally H-Y negative homogametic sex but not in non-gonadal tissues. This is consistent with the view that oestrogens act via H-Y antigen in the organization of the avian gonad.

H-Y antigen in the teleost

H-Y antigen, presumably the product of mammalian testis-determining genes, has been detected in three species of teleost fish, Xiphophorus maculatus. Haplochromis burtoni, and Oryzias latipes, and in hybrids of the genus Tilapia. In X. maculatus H-Y was most readily detected in YY males, suggesting that a genetic determinant of H-Y antigen expression may exist on the teleost Y-chromosome. Although H-Y was detected in males and not in feamles in each of the species that we studied, male heterogamety has not been firmly established for H. burtoni. Thus despite the extreme phlyogenetic conservation of H-Y genes and their association with the Y-chromosome, it remains open to question whether H-Y will always be found in the heterogametic sex, and whether serologically defined H-Y antigen plays any part in the differentiation of the teleost gonad.