• Development and Reproduction
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• v.22 no.3
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• pp.213-223
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• 2018

Ultrastructural studies on oocyte differentiation and vitellogenesis in the oocytes of female Kareius bicoloratus were investigated by transmission electron microscopy. The Golgi complex in the cytoplasm is involved in the formation of yolk vesicles that contain yolk carbohydrates in the yolk vesicle of oocytes in the early vitellogenic phase. In this phase, many pinocytotic vesicles (PVs), which are formed by pinocytosis, contain yolk precursors (exogenous substances). These substances are associated with exogenous heterosynthetic vitellogenesis. In yolked oocytes in the late vitellogenic phase, two morphologically different bodies, which formed by modified mitochondria, appear in oocytes. One is a multivesicular body (synthesized by autosynthetic vitellogenesis), and the other is a yolk precursor (an exogenous substance formed by heterosynthetic vitellogenesis). The multivesicular bodies (MVB) are taken into the yolk precursors (YP) and are transformed into primary yolk globules. However, after the YP mix with exogenous PVs near the zona pellucida, they are transformed into primary yolk globules. Vitellogenesis of this species occurs via endogenous autosynthesis and exogenous heterogenesis. Vitellogenesis occurs through endogenous autosynthesis, which involves the combined activity of the Golgi complex, mitochondria and MVB formed by modified mitochondria. However, heterosynthesis involves pinocytotic incorporation of extraovarian precursors (such as vitellogenin in the liver) into the zona pellucida (via granulosa cells and thecal cells) of the yolked oocyte.

• Development and Reproduction
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• v.12 no.2
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• pp.195-202
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• 2008

The gonadosomatic index, germ cell differentiation, and the ovarian cycle in female jicon scallop, Chlamys farreri were studied by histologic and cytologic observations. In the early vitellogenic oocyte, the Golgi complex, mitochondria and rough endoplasmic reticulum were involved in the formation of lipid droplets. In the late vitellogenic oocyte, exogenous substances, namely, glycogen particles and lipid granular substances appeared in the germinal epithelium passed into the ooplasm through the microvilli of the envelope. Yolk granules and multivesicular bodies were involved in the formation of proteinecious yolk granules in the late vitellogenic oocyte. Vitellogenesis occurrs by endogenous autosynthesis and exogenous heterosynthesis. The auxiliary cells function as nutritive cells in the formation and development of the previtellogenic and early vitellogenic oocytes in their earlr stages. Monthly changes in the gonadosomatic index were closely associated with ovarian developmental phases. The reproductive cycle of this species can be classified into five stages: early active stage (January to March), late active stage (March to April), ripe stage (April to August), partially spawned stage (June to August), and spent/inactive stage (August to December). Spawning occurred from June to August, and the major spawning season was from July to August when the sea water was at high temperature.

• Journal of Embryo Transfer
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• v.5 no.1
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• pp.1-20
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• 1990

Follicular atresia is a universal and characteristic phenomenon of both non-mammalian and mammalian vertebrates. Generally it is estimated that greater than 99% of follicles become atretic in higher domestic animals and human. The number of selected follicles developing to the preovulatory stage are thus fewer. Follicles can become atretic at any stage of development. The previous studies emphasized on descriptive and retrospect aspects of a limited population of the fully grown preovulatory follicle. The main efforts in ovarian physilogical researches are focused on follicular development culminating in ovulation but recent advances have resulted in a better understanding of atresia. Nowadays, recent studies are concentrated on the induction of atresia in a selected population of follicles and of the associated cellular, endocrine, biochemical and molecular changes. The factors initiating atresia and follicle selections are worthy of investigations. Another intriguing question is whether one can predict when a follicle will become atretic, i.e., what biochemical markers indicate that a follicle is destined for atresia. It is generally agreed that atretic process may vary even in antral follicles at different stages of their differentiations and among species. The dicisive factors are follicular responsiveness and the hormonal milieu. Some generalizations can be made on the basis of experimental induction of atresia. Alteration of the pattern of follicular steroid production is associated with the initiation stage of atretic process. Atresia appears to be a process unfolding gradually and affecting progressively in increasing number of functions and components of the follicle. The oocyte may be the latest to be afflicted in the atretic process. The high steroidogenic activity of atretic follicles lends support to the notion that atresia is not necessarily a degenerative process and that atretic follicles may play an essential role in ovarian physiology. The simultaneous occurence of growth and atretic processes may render the search for regulatory mechanisms involved in atresia difficult extremely. The questions such as how follicles are selected to undergo ovulation rather than atresia or what the mechanism of atresia is remain unanswered. However, the factors regulating or modifying ovarian hormonal milieu for the initiation of follicular growth and maturation or of atresia are being elucidated.

• The Korean Journal of Malacology
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• v.27 no.3
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• pp.261-271
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• 2011

The gametogenic cycle, the spawning season and the biological minimum sizes in female and male Protothaca (Notochione) jedoensis were investigated by quantitative statistical analysis. In females, monthly changes in the percents of the follicle areas to the ovarian tissue areas and the percents of the oocyte areas to the ovarian tissue areas increased in February and reached the maximum in April, and then gradually decreased from May to July, with the spawning peak between June and July. In males, monthly changes in the percents of the testicular tissue areas to total tissue areas and the percents of the spermatogenic stage areas to the testicular tissue areas increased in February and reached the maximum in April, and then showed a rapid decrease from May to July. From these data, it is apparent that the number of spawning seasons in female and male P. (N.) jedoensis occurred once a year, from May to July. Therefore, P. (N.) jedoensis in both sexes showed a unimodal gametogenic cycle during the year. Compared the gametogenic cycle by quantitative statistical analysis in 2007 with the previous qualitative results of this species, the results of the gametogenic cycle calculated by quantitative statistical analysis showed some differentiations in the spawning seasons evaluated by the gonad index by qualitative histological analysis. The intervals of the beginning of two spawning seasons showed one month between the results of quantitative and qualitative analyses. The biological minimum sizes (considering to 50% of group sexual maturity) in female and male clams by quantitative analysis of this species are 32.01 mm in shell length in females and 30.58 mm in males, respectively. According to the mean shell length fitted to von Bertalanffy's equation, 30.58 and 32.01 mm in shell length were considered to be two years old. Therefore, we assume that both sexes of this population begin reproduction from two years of age.