This study presents novel findings on the dynamics of growing oocytes in the ovary of the medaka fish, Oryzias latipes. In the ovary of mature females, all follicles are anchored tightly to the ...abdominal ovarian rete via fibrous follicular stalks on the follicle surface. The follicular stalks lie at the end of the follicle opposite the site of its attachment to the ovarian wall. Various lengths of the follicular stalks reflect the spatial arrangement of follicles in the ovary. Herein, a line that connects the follicular stalk to the opposite side of the follicle toward or attaching to the ovarian wall is called the follicle axis. The animal-vegetal axis in late stage III oocytes is already recognizable as a line that connects the center of the oocyte nucleus and the vegetal pole area; this is ascertainable by the morphological landmark of a compact distribution of granulosa cells or rudimentary attachment filaments. In growing oocytes later than stage V, the beginning of vitellogenesis, the tufted attachment filaments are located on a discrete region of the vegetal pole area. Our observations reveal that during growth, oocytes are arranged randomly between the animal-vegetal axis and the follicle axis, whereas the vegetal pole area of full-grown oocytes in preovulatory follicles turns close to the inner surface of the ovarian wall, from which mature oocytes subsequently ovulate into the ovarian lumen. It is suggested that in the O. latipes ovary, mature oocytes always transpose the vegetal pole area to the ovulatory site of the ovarian wall prior to ovulation. The expulsion of mature oocytes from the vegetal pole appears to be the regular mode of ovulation in O. latipes.
Involvement of
Ad4BP/
SF-
1 was investigated using the serial sex changing goby
Trimma okinawae. First, a cDNA encoding
Ad4BP/
SF-
1 was cloned from ovarian follicles. The open reading frame of goby
...Ad4BP/
SF-
1 encodes a protein of 489 amino acids.
Ad4BP/
SF-
1 was expressed in gonadal tissues, brain, and kidney. Second, transcript levels of
Ad4BP/
SF-
1 were measured in the ovary and testis of the same individuals. Expressions were related to sexual phases. Moreover, ovarian expression of
Ad4BP/
SF-
1 increased during vitellogenesis and declined sharply during the post-vitellogenic period. Finally, the expression profile of
Ad4BP/
SF-
1 was measured during serial sex change in the ovary.
Ad4BP/
SF-
1 increased in parallel with the onset of the female-phase and decreased as female became male. Therefore,
Ad4BP/
SF-
1 probably acts as an important indirect regulator of oocyte growth and maturation at female-phase of serial sex changing gobiid fish
T. okinawae.
Commercially significant groupers are protogynous hermaphrodites. Since their sex change from female (ovary) to male (testis) occurred in a larger size and older age, capturing or maintaining males ...in the aquaculture farm is very difficult. In the present study, juvenile longthooth groupers (2+ years old) were implanted with two doses of 17alpha-methyltestosterone (MT) cholesterol pellet (2 mg or 5 mg MT kg-1 BW) for the induction of artificial sex reversal. Individuals were sampled at 30 and 80 days after treatment. All the control group fish had immature ovaries contained with primary oocytes and germ cells. Fish treated with MT for 30 days had sex-transitional gonad consisted of few primary oocytes and testicular tissues. By using immunohistochemistry, we identified the proliferating and apoptotic cells in the gonad of this sexual stage. After 80 days for MT treatment, gonads of all individuals were filled with germ cells at all stages of spermatogenesis, and the newly formed efferent duct contained active spermatozoa. Since sperm motility was confirmed, MT treatment successfully induced functional sex reversal in pre-pubertal longtooth grouper. This method may dramatically reduce the cost and time required for the production of longtooth grouper.
A subset of gustatory cells are serotonin immunoreactive (ir) in the mammalian taste bud. In the taste bud of lamprey, elongated gustatory-like cells are also serotonin-ir. In contrast, flattened ...serotonin-ir cells are located only in the basal region of the taste buds in the teleosts and amphibians. These serotonin-ir cells are termed as basal cells. To evaluate the evolution and diversity of serotonergic cells in the taste bud of amniote animals, we explored the distribution and morphology of serotonin-ir cells in the taste buds of ancestral actinopterygian fish (spotted gar, sturgeon,
Polypterus senegalus
) and elasmobranch (stingray). In all examined animals, the taste buds contained serotonin-ir cells in their basal part. The number of serotonin-ir basal cells in each taste bud was different between these fish species. They were highest in the stingray and decreased in the order of the
Polypterus
, sturgeon, and gar. While serotonin immunoreactivity was observed only in the basal cells in the taste buds of the ancestral actinopterygian fish, some elongated cells were also serotonin-ir in addition to the basal cells in the stingray taste buds. mRNA of
tryptophan hydroxylase 1
(
tph1
), a rate-limiting enzyme of the serotonin synthesis, is expressed in both the elongated and basal cells of stingray taste buds, indicating that these cells synthesize the serotonin by themselves. These results suggest that the serotonin-ir basal cells arose from the ancestor of the cartilaginous fish, and serotonin-ir cells in the elasmobranch taste bud exhibit an intermediate aspect between the lamprey and actinopterygian fish.
Artificial sex change was induced within two full moons by an aromatase inhibitor (AI; 1 mg/fish) during the breeding season to establish the quickest method of sex change and natural spawning of the ...honeycomb grouper (
Epinephelus merra). The sex change from female (ovary) to male (testis) occurred during the time between the two full moons (3 weeks) following AI implantation, and the efferent ducts of sex-changed males were filled with sperm. To examine sperm fertility, sex-changed males were mated with natural, normal females and produced fertilized eggs. Most of the hatched larvae grew normally without any morphological deformities. Therefore, the use of this method which is the quickest known sex change method using AI, may contribute to quality sperm production for grouper aquaculture.
To clarify the cause of sex change recovery after the withdrawal of androgen treatment, immature female Malabar grouper were fed a diet containing 17alpha-methyltestosterone (MT) at 50 μg/g for 7 mo ...and then a normal diet for 6 mo. The MT brought about precocious sex change from immature ovaries to mature testes with active spermatogenesis, including the development of spermatozoa, and sex change reversed soon after MT treatment withdrawal. This result indicates that precocious sex change in immature Malabar grouper with oral MT treatment is impermanent. The expression of three steroidogenic enzymes (Cyp11a, Cyp19a1a, and Cyp11b) in the gonads of the Malabar grouper were analyzed immunohistochemically at the end of the 7-mo treatment. No apparent differences were seen in the expression pattern of these enzymes between the mature testes of MT-treated fish and the immature ovaries of control fish. In addition, serum estradiol-17beta and 11-ketotestosterone levels in treated fish were the same as those in control fish. These results indicate that in the case of immature Malabar grouper MT might have little effect on endogenous steroidogenesis during precocious sex change even though it induced active spermatogenesis in the gonads of treated fish. From these results, we also concluded that MT might have little effect on the steroidogenic endocrine pathway, and this is one cause of sex change recovery after treatment withdrawal.
In order to obtain basic information about the role played by endogenous sex hormones in bringing about sex changes in the serial‐sex changing gobiid fish Trimma okinawae, the gonadal structure of ...male and female phases were observed histologically. Steroid‐producing cells (SPC; Leydig cells in a testis) were observed ultrastructurally in the ovaries and testes of both female‐phase and male‐phase fish. In addition, gonadal expression of P450 cholesterol side‐chain‐cleavage (scc) was examined immunohistochemically. Gonads of fish in female and male phases were observed to have both ovaries and testes simultaneously. Female‐phase fish had matured with many developed vitellogenic oocytes, while male‐phase individuals had immature ovaries with many numbers of previtellogenic oocytes at the perinucleolus stage. Testes of fish in different sexual phases had active spermatogenic germ cells. Organellae of SPC in the ovaries of female‐phase fish had active structures of steroid production. In contrast, SPC in the ovaries of male‐phase fish did not show active structures of steroid production. Immunopositive reactions against the scc antibody in the ovaries of female‐phase fish were very strong, but immunoreactions in the ovaries of male‐phase fish were very weak. In the testis, moderate immunopositive signals were obtained from dual‐phase male/females.
Size-advantage and low-density models have been used to explain how mating systems favor hermaphroditism or gonochorism. However, these models do not indicate historical transitions in sexuality. ...Here, we investigate the evolution of bidirectional sex change and gonochorism by phylogenetic analysis using the mitochondrial gene of the gobiids
Trimma
(31 species),
Priolepis
(eight species), and
Trimmatom
(two species).
Trimma
and
Priolepis
formed a clade within the sister group
Trimmatom
. Gonadal histology and rearing experiments revealed that
Trimma marinae
,
Trimma nasa
, and
Trimmatom
spp. were gonochoric, whereas all other
Trimma
and
Priolepis
spp. were bidirectional sex changers or inferred ones. A maximum-likelihood reconstruction analysis demonstrated that the common ancestor of the three genera was gonochoristic. Bidirectional sex change probably evolved from gonochorism in a common ancestor of
Trimma
and
Priolepis.
As the gonads of bidirectional sex changers simultaneously contain mature ovarian and immature testicular components or vice versa, individuals are always potentially capable of functioning as females or males, respectively. Monogamy under low-density conditions may have been the ecological condition for the evolution of bidirectional sex change in a common ancestor. As
T. marinae
and
T. nasa
are a monophyletic group, gonochorism should have evolved from bidirectional sex change in a common ancestor.
Recent studies have suggested that the hypothalamic-pituitary-gonadal axis is involved in gonadal sex change in sex-changing teleosts. However, its underlying mechanism remains largely unknown. In ...this study, we focused on the distinct roles of two gonadotropins (GTHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), in the protogynous hermaphrodite teleost, honeycomb grouper (Epinephelus merra). First, we investigated the expression pattern of mRNAs for GTH subunits (cga, fshb, and lhb) in the pituitaries from fish at the different sexual phases. Real-time RT-PCR analyses showed that fhsb mRNA levels in the female pituitary were low. However, fshb transcripts increased dramatically in association with testis development. In contrast, levels of cga and lhb mRNAs did not significantly vary during sex change. In addition, immunohistochemical observations of Fshb- and Lhb-producing cells in the pituitary, through the use of specific antibodies for detections of teleost GTH subunits, were consistent with sexually dimorphic expression of Fshb. In order to identify the role of GTH in gonad of honeycomb grouper, we treated females with bovine FSH (50 or 500 ng/fish) or LH (500 ng/fish) in vivo. After 3 wk, FSH treatments induced female-to-male sex change and up-regulated endogenous androgen levels and fshb transcripts, whereas LH treatment had no effect on sex change. These results suggest that FSH may trigger the female-to-male sex change in honeycomb grouper.
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