Implication of Catecholamines During Spawning in Marine Bivalve Molluscs

Summary

During the tail-bud stage of Ascidiella aspersa embryogenesis, the test cells or innermost cells of the egg envelope manifest locomotive activities. Light microscopy further reveals that the adhesive behaviour of test cells changes in the course of embryogenesis. Mechanical dechorionation experiments performed on 846 embryos demonstrate that up to the tail-bud stage all test cells are attached to the inner surface of the chorion. The embryo is completely devoid of test cells. At the onset of larval tunic secretion, increasing numbers of test cells settle on the embryo until all test cells adhere to it. This switch in adhesive properties is completed within 65 min. The hatched larva carries the entire complement of test cells until the onset of metamorphosis. SEM and observations show that test cells do not establish direct cell-to-cell contacts to ectodermal cells but attach to the larval tunic.     

Advanced sexual maturation before marine migration of Anguilla bicolor bicolor and Anguilla marmorata at Réunion Island

Maturing sub-adults of two species of anguillid eels (a female Anguilla bicolor bicolor and a male Anguilla marmorata ) were collected for the first time at Réunion Island, western Indian Ocean. Both were silver eels, i.e. maturing eels at the onset of their spawning migration, and characterized by advanced sexual maturation that has been only observed in Anguilla dieffenbachii from New Zealand.     

A sex cord‐like structure and some remarkable features in early gonadal sex differentiation in the marine teleost Siganus guttatus(Bloch)

Several notable features of early gonadal sex differentiation in the golden rabbitfish Siganus guttatus are described including the first report among teleosts of a distinctive dual structure, consisting of somatic cells directly enclosing germ cells (sex cord‐like structure, SCS) and outer somatic tissue surrounding the SCS, in both undifferentiated and early differentiated gonads. Germ cells occurred and proliferated exclusively in the SCS during the process of ovarian and testicular differentiation. A second remarkable characteristic was the delayed germinal cell proliferation for oogenesis in the ovary, that commenced simultaneously with that in the testis, a relatively long time after the onset of somatic development. These observations suggest the possibility that sex differentiation of germ cells is preceded by some sex specific changes in somatic components of the SCS that are light‐microscopically indistinguishable between the sexes. The third unique feature was the detachment of gonadal tissue, including both somatic and germ cells, into the ovarian cavity in the ovary and into the seminiferous lobules and main seminal duct in the testis. This phenomenon occurred in the testis, forming the efferent duct network after 73 days post‐hatch (DPH), and in the ovaries, forming the ovigerous lamellae and regulating the number of oocytes attaining full maturation at c . 129 DPH.     

橘小实蝇染色体研究与相关技术探讨

以橘小实蝇Bactroceradorsalis(Hendel)性腺和唾液腺为材料,采取改良苯酚品红染色后压片法,制备染色体标本。对橘小实蝇进行染色体组型研究和唾液腺染色体形态学的观察。结果表明:橘小实蝇成虫性腺染色体数目为2n=12条,染色体长度基本呈连续性变化,其性染色体属于XX/XY型。幼虫唾液腺染色体包含5条较长的多线染色体,与成虫常染色体相对应。实验显示苯酚品红染色后压片为制备染色体标本简单有效的方法。     

Cyclic variations of gonad development of snow trout,Schizopyge niger from the river Jhelum of Kashmir Himalaya

The aim of the present study was to know the cyclic changes in gonadal maturation and to investigate the various developmental stages of oocytes and testicular germ cells of snow trout, Schizopyge niger. A total of 316 fish specimens were procured from three sites of river Jhelum during November 2016 to October 2017 and the histological analysis of their gonad was carried out. The results of the present study indicates that the male population was found significantly (p < 0.05) higher compared to female population and were reported as (1.6:1; M:F). The highest mean GSI value was recorded in male (12.24 ± 0.89) during the month of March and for female (13.74 ± 0.92) also in the month of March, which indicated that the gonadal development reached its peak during this month. The highest mean oocyte diameter was 1.04 ± 0.20 mm observed in March, showing that the oocyte reached its maturity during this month. Histological study of ovary revealed the evidence of vitellogenic yolk granule stage and ripe mature stage from December to April. While in case of male, four stages of spermatogenesis were distinguished and spermatozoa were highly abundant in the months of March and April. Mean ± SE of absolute fecundity was 3,224 ± 421 eggs and also, the relative fecundity was 69 egg/g body weight. Based on the results of GSI and the analysis of gonad histology, it was observed that the peak breeding season of S. niger occurred in the month of March. It was also noted that spawning period of this fish begins in the month of February and lasts till April with a peak breeding season in the month of March. The present study will provide a baseline information about the appropriate peak breeding of the fish, which will be useful for artificial breeding as well for prevention of fishing from natural habitat.     

Dissecting Cell Lineage Specification and Sex Fate Determination in Gonadal Somatic Cells Using Single-Cell Transcriptomics

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Ecotoxicological evaluation of tributyltin toxicity to the equilateral venus clam, Gomphina veneriformis (Bivalvia: Veneridae)

Tributyltin (TBT) is the most common pesticide in marine and freshwater environments. To evaluate the potential ecological risk posed by TBT, we measured biological responses such as growth rate, gonad index, sex ratio, the percentage of intersex gonads, filtration rate, and gill abnormalities in the equilateral venus clam (Gomphina veneriformis). Additionally, the biochemical and molecular responses were evaluated in G. veneriformis exposed to various concentrations of TBT. The growth of G. veneriformis was significantly delayed in a dose-dependent manner after exposure to all tested TBT concentrations. After TBT was administered to G. veneriformis, the gonad index decreased and the sex balance was altered. The percentage of intersex gonads also increased significantly in treated females, whereas no intersex gonads were detected in the solvent control group. Additionally, intersex gonads were detected in male G. veneriformis specimens exposed to relatively high TBT concentrations (20 μg L⁻¹). The filtration rate was also reduced in a dose-dependent manner in TBT-exposed G. veneriformis. We also noted abnormal gill morphology in TBT-exposed G. veneriformis. Furthermore, increases in antioxidant enzyme activities were observed in TBT-exposed G. veneriformis clams, regardless of dosage. Vitellogenin gene expression also increased significantly in a dose-dependent manner in G. veneriformis exposed to TBT. These results provide valuable information regarding our understanding of the toxicology of TBT in G. veneriformis. Moreover, the responses of biological and molecular factors could be utilized as information for risk assessments and marine monitoring of TBT toxicity.     

Cross talk between germ cells and gonadal somatic cells is critical for sex differentiation of the gonads in the teleost fish, medaka (Oryzias latipes)

To evaluate the possible role of germ cells on sex differentiation of the gonads in vertebrates, the teleost fish, medaka ( Oryzias latipes ), was used to generate a gonad without germ cells. The germ cell-deficient medaka reveals multiple effects of germ cells on the process of sex differentiation. The previously isolated mutant medaka, hotei , with the excessive number of germ cells may support the contention that the proliferation of germ cells is related to feminization of the gonad. Futhermore, we show that two modes of proliferation for either maintenance of germ cells or commitment to gametogenesis are important components of the sex differentiation of medaka developing gonads. An intimate cross talk between germ cells and gonadal somatic cells during the sex differentiation will be discussed.     

石斑鱼性反转相关基因 ECaM的克隆及表达特征分析

用甲睾酮片饲喂 2 ～ 4 龄赤点石斑鱼 (Epinephelus akaara) , 6 周后 90% 以上的雌鱼性逆转为功能性雄鱼 . 运用抑制性差减杂交技术 (SSH) ,结合 SMART cDNA 合成和 RACE-PCR 方法,从性反转雄鱼性腺中克隆到钙调蛋白基因 (ECaM). 该基因 cDNA 全长为 582 bp ,开放阅读框长 450 bp ,编码的蛋白质由 149 个氨基酸组成, 5 ′端非编码区 74 bp , 3 ′端非编码区 58 bp. 虚拟 RNA 印迹表明, ECaM 在性反转雄鱼性腺中表达,而在正常雌鱼性腺中表达微弱 . 各种组织的半定量 RT-PCR 显示, ECaM 在脑、心、肝、脾、肾都有转录,在精巢和下丘脑中表达水平较高,而在肌肉中表达甚弱 . 性反转不同时期性腺的半定量 RT-PCR 及蛋白质印迹表明,性逆转过程中性腺里 ECaM 的表达量逐渐增加 . 上述结果提示钙调蛋白可能在赤点石斑鱼性逆转过程中发挥着作用, ECaM 可能是促使石斑鱼由雌向雄转变的重要功能基因之一 .