Karyological confirmation of conspicuous ZW sex chromosomes in two species of Pacific anguilloid fishes (Anguilliformes: Teleostomi)

Dmrt1 (doublesex and mab-3-related transcription factor 1) expression during gonadal development and spermatogenesis in the Japanese eel

Dmrt1, doublesex- and mab-3-related transcription factor-1, has been suggested to play critical roles in male gonadogenesis, testicular differentiation and development, including spermatogenesis, among different vertebrates. Vasa is a putative molecular marker of germ cells in vertebrates. In this study, we cloned the full-length dmrt1 cDNA from Japanese eel, and the protein comprised 290 amino acids and presented an extremely conserved Doublesex and Mab-3 (DM) domain. Vasa proteins were expressed in gonadal germ cells in a stage-specific manner, and were expressed at high levels in PGC and spermatogonia, low levels in spermatocytes, and were absent in spermatids and spermatozoa of Japanese eels. Dmrt1 proteins were abundantly expressed in spermatogonia B cells, spermatocytes, spermatids, but not in spermatozoa, spermatogonia A and Sertoli cells. To our knowledge, this study is the first to show a restricted expression pattern for the Dmrt1 protein in spermatogonia B cells, but not spermatogonia A cells, of teleosts. Therefore, Dmrt1 might play vital roles at the specific stages during spermatogenesis from spermatogonia B cells to spermatids in the Japanese eel. Moreover, the Dmrt1 protein exhibited a restricted localization in differentiating oogonia in the early differentiating gonad (ovary-like structure) of male Japanese eels and in E2-induced feminized Japanese eels. We proposed that dmrt1 may be not only required for spermatogenesis but might also play a role in oogenesis in the Japanese eel.

Gonadal development and expression of sex-specific genes during sex differentiation in the Japanese eel

The process of gonadal development and mechanism involved in sex differentiation in eels are still unclear. The objectives were to investigate the gonadal development and expression pattern of sex-related genes during sex differentiation in the Japanese eel, Anguilla japonica. For control group, the elvers of 8-10cm were reared for 8months; and for feminization, estradiol-17β (E2) was orally administered to the elvers of 8-10cm for 6months. Only males were found in the control group, suggesting a possible role of environmental factors in eel sex determination. In contrast, all differentiated eels in E2-treated group were female. Gonad histology revealed that control male eels seem to differentiate through an intersexual stage, while female eels (E2-treated) would differentiate directly from an undifferentiated gonad. Tissue distribution and sex-related genes expression during gonadal development were analyzed by qPCR. The vasa, figla and sox3 transcripts in gonads were significantly increased during sex differentiation. High vasa expression occurred in males; figla and sox3 were related to ovarian differentiation. The transcripts of dmrt1 and sox9a were significantly increased in males during testicular differentiation and development. The cyp19a1 transcripts were significantly increased in differentiating and differentiated gonads, but did not show a differential expression between the control and E2-treated eels. This suggests that cyp19a1 is involved both in testicular differentiation and development in control males, and in the early stage of ovarian differentiation in E2-treated eels. Importantly, these results also reveal that cyp19a1 is not a direct target for E2 during gonad differentiation in the eel.

Cytogenetical studies in five Atlantic Anguilliformes fishes

The order Anguilliformes comprises 15 families, 141 genera and 791 fish species. Eight families had at least one karyotyped species, with a prevalence of 2n = 38 chromosomes and high fundamental numbers (FN). The only exception to this pattern is the family Muraenidae, in which the eight species analyzed presented 2n = 42 chromosomes. Despite of the large number of Anguilliformes species, karyotypic reports are available for only a few representatives. In the present work, a species of Ophichthidae, Myrichthys ocellatus (2n = 38; 8m+14sm+10st+6a; FN = 70) and four species of Muraenidae, Enchelycore nigricans (2n = 42; 6m+8sm+12st+16a; FN = 68), Gymnothorax miliaris (2n = 42; 14m+18sm+10st; FN = 84), G. vicinus (2n = 42; 8m+6sm+28a; FN = 56) and Muraena pavonina (2n = 42; 6m+4sm+32a; FN = 52), collected along the Northeastern coast of Brazil and around the St Peter and St Paul Archipelago were analyzed. Typical large metacentric chromosomes were observed in all species. Conspicuous polymorphic heterochromatic regions were observed at the centromeres of most chromosomes and at single ribosomal sites. The data obtained for Ophichthidae corroborate the hypothesis of a karyotypic diversification mainly due to pericentric inversions and Robertsonian rearrangements, while the identification of constant chromosome numbers in Muraenidae (2n = 42) suggests a karyotype diversification through pericentric inversions and heterochromatin processes.

Heteromorphic sex chromosomes of lizardfish (Synodontidae): focus on the ZZ-ZW1W2 system in Trachinocephalus myops

The karyotype and DNA content of four lizardfish species (family Synodontidae), that is, Saurida elongata, Synodus ulae, Synodus hoshinonis and Trachinocephalus myops, were analyzed. The karyotype of T. myops significantly differed from that of the other three species having diploid chromosome number of 48 with mainly acrocentric chromosomes and the ZZ-ZW sex chromosome system. The chromosome number of male T. myops was 2n = 26, while that of female T. myops was 2n = 27. The karyotype consisted of 11 pairs of metacentrics, one pair of acrocentrics and, in addition, two large metacentrics in the male and a single large metacentric, a distinctly small subtelocentric and a microchromosome in the female. C-banding demonstrated that in the female the subtelocentric chromosome and the microchromosome were heterochromatic. The karyotype of T. myops was thought to be derived from a 48 chromosome type synodontid fish through the involvement of Robertsonian rearrangement; the rearrangement of the sex chromosomes proceeded during karyotype evolution. Among the chromosomes, the large metacentrics were determined to be neo-Z (a fusion of the original Z and an autosome), the microchromosomes the W1 (originally W), and the subtelocentric chromosomes the W2 (derived from an autosome pair). The miniaturization of W1 and W2 chromosomes and their heterochromatinization suggested that sex chromosomes in this species have been already highly differentiated. The findings on DNA content implied that the karyotype of T. myops evolved by centric fusion events without loss in DNA amount.

[Classification Of Planorbidae Cellected From Geum River Basin]

The distribution, external morphology, radula, chromosome numbers of Planorbidae snails were studied. 1. The specimens were collected at four stations in Nonsangun, Kongjugun, and Daedukgun which are located around Geum river. Three genera and three species of Planorbidae, Hippeutis cantori, Segmentina hemisphaerula and Gyraulus convexiusculus, were collected. H. cantori was the most abundant species among the three species. G. convexiusculus was the least abundant one. Each species could be identified on the basis of its external characteristic, since the periphery of each species has a peculiar shape. H. cantori was the largest one among the three species. The radula formula of each species was very similar to other species. The size of radula was proportional to the size of shell. The radula formulae of H. cantori, S. hemisphaerula, and G. convexiusculus were 29:1:29, 23:l:23, and 16:1:16 respectively. The difference of radula formula could be found in the total numbers of laternal and marginal teeth. The haploid chromosome number of H. cantori was eighteen (n=18). S. hemisphaerula and G. convexiusculus were assumed to be same in their chromosome numbers (n=18).

Elevated sister chromatid exchange rate in lymphocytes of the European eel (Anguilla anguilla) with cauliflower tumor

Sister chromatid exchange (SCE) frequency and chromosomal aberration were studied in cultured lymphocytes from the European eel (Anguilla anguilla) with cauliflower tumors. SCE was significantly increased in the affected fishes compared with normal controls, whereas chromosomal aberration did not. In comparison to normal cells, the lymphocytes responding to phytohemagglutinin M (PHA-M) in cultures from tumorous eels showed no evidence of cell cycle retardation. A possible mechanism for elevation of SCE and the significance of this finding relation to the etiology were discussed.