JSPS Postdoctoral Research Fellow TBRC, University of the Ryukyus Sesoko 3422, Motobu, Okinawa 905-0227, Japan Cell:+81-90-7587-7387 Email:alam.tbrc@gmail.com
Ph.D (Molecular Endocrinology), University of the Ryukyus, Japan
M.Sc. (Reproductive Biology/Endocrinology), University of the Ryukyus, Japan
M.S. (Fish Biology and Genetics), Bangladesh Agricultural University, Bangladesh
B.Sc. Fisheries (Hons), Bangladesh Agricultural University, Bangladesh Short training course (Molecular genetic softwares), University of Aarhus, Denmark
FELLOWSHIPS AND AWARDS
Japan Society for the Promotion of Science (JSPS) Research Fellowship, University of the Ryukyus (2008-2010).
Scholarship from the Ministry of Education, Government of Japan (Monbukagakusho) for PhD program at University of the Ryukyus (October, 2005-September, 2008).
Scholarship from the Ministry of Education, Government of Japan (Monbukagakusho) for Master’s program at University of the Ryukyus (October, 2004-September, 2005).
Short-term(three months) training fellowship from Associate Professor Vibeke Simenson, Aarhus University, Denmark (November 2002-January 2003).
National Science and Technology (NST) fellowship, Ministry of Science and Technology, Government of Bangladesh (April 2000-September 2000).
RESEARCH INTEREST
Changing from one sex to another is not just a biological ingenuity; it is a way of life in some hermaphrodite fish. Honeycomb grouper is a protogynous hermaphrodite, inhabiting coral reefs areas in Asia-Pacific regions. They born as female and commence sex change, when they grow approximately 13-17cm in total length, coinciding with the sexual maturity, i.e. it usually happens when they complete their one or two spawning cycle(s). This is an interesting event, but what triggers this transformation is not known yet. The sex hormones are likely factors to regulate this change, however, which hormones and when exactly they act on germ cells to change their fate are as yet unknown. Recently, our laboratory has unveiled a key factor that is essential for maintenance of female sex, i.e. estradiol-17beta (E2). One of my plan was to unveil what triggers testicular differentiation during the onset of sex change. At the first phase of my research I have found that androgen-producing cells are located in the tunica near blood vessel of ovary. According to my investigation, this site plays important role in producing androgen, that eventually triggers male germ cell development in the ovary and initiate sex change.
ON-GOING PROJECTS
How does FSH and FSHR regulates androgen biosynthesis in Leydig cells?
Abstract: Determination of the sex and gonadal maturity of fish is necessary for successful commercial aquaculture operations. Sex identification is problematic in grouper fish, because they change sex at certain ages or sizes. Here we represent an accurate and reliable method for sex determination of the live grouper, using 5-10 mg gonadal tissue samples, harvested using non-lethal gonadal biopsy. Sex and sexual maturity of biopsied individuals were determined using standard histological method. All biopsied fish survived and there were no serious infections resulting from the surgery. Therefore, this biopsy technique is a simple and cost-effective tool for grouper fishery management.
Abstract: The honeycomb grouper (Epinephelus merra) is one of the smallest members of the Serranidae family and is often used to study protogynous sex change. To determine the role of the male-determining gene Dmrt1 and the ovarian-specific gene Foxl2 in sex change, we cloned these two markers from E. merra gonads by reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). Two isoforms, Dmrt1a and Dmrt1b, resulted from alternative splicing in the coding region, causing the insertion of one glutamine residue in Dmrt1b. RT-PCR revealed that Dmrt1 was expressed only in the gonads, with higher levels in the testis than in the ovary. cDNA encoding Foxl2 was isolated from the ovary; Foxl2 was expressed extensively in the brain, pituitary, gonads, and gill, with its highest level in the ovary, indicating a potential role for Foxl2 in the brain-pituitary-gonad axis. Real-time quantitative RT-PCR analyses showed that Foxl2 mRNA expression was significantly downregulated from the late transitional phase to the completion of sex change. Conversely, Dmrt1 expression increased with the progression of spermatogenesis and continued until the formation of the testis. The expression profiles of these two sex-specific marker genes corresponded closely with the histological process of sex change. The down-regulation of Foxl2 most likely facilitates oocyte degeneration, whereas the up-regulation of Dmrt1 causes the proliferation of gonial germ cells into spermatogina and initiates sex change. (C) 2008 Elsevier Inc. All rights reserved.
Abstract: Groupers are commercially important coral reef fishes because of their excellent flavor and high price. Due to their sex changing nature, commercial aquaculture operations have not yet been developed for groupers. Sex steroids play a critical role in the initiation of sex change, but their exact function and mechanism of action are unknown. We have investigated the role of sex steroids in protogynous sex change using the honeycomb grouper, Epinephelus merra, for a number of years. Our studies have shown that sex steroids play a major role in sex change. In this review, we integrate our findings to better understand the mechanism of sex change in groupers.
Notes: Conference on Ecophysiology in Marine Organisms OCT 03-04, 2006 Natl Taiwan Ocean Univ, Keelung, TAIWAN
Abstract: Efferent duct (ED) differentiation was examined histologically during female-to-male sex change in the honeycomb grouper Epinephelus merra. During natural sex change, ED differentiation began with the appearance of slit-like structures between the stromal tissue and the tunica ovary and small oval-shaped spaces within the wall of the ovarian cavity, accompanied by oocyte degeneration and the initiation of spermatogenesis, i.e. the early transitional phase. In the late transitional phase, ED structure formation expanded and further ED differentiation occurred, including the rapid multiplication of spermatogonial germ cells. In sex-changed males, the slit-like structures increased in size, fused with each other and finally formed a well-developed ED. The oval-shaped spaces also increased in size and fused to form an ED. In contrast, during artificial sex change, induced by aromatase inhibitor (AI, 1 mg kg(-1)), ED differentiation in E. merra was first observed as the appearance of slit-like structures and small oval-shaped spaces in the restructuring gonads in the third week after AI treatment. These were accompanied by oocyte degeneration and the proliferation of gonial germ cells into spermatogonia. In the fifth week, the rapid multiplication of spermatogonial germ cells, increases in 11-ketotestosterone (11-KT), and further differentiation of EDs were observed. Sex-changed males had testes containing sperm in the completely differentiated EDs; the significantly highest levels of 11-KT were observed in the sixth week. Simultaneous increases in 11-KT and initiation of ED differentiation were observed, suggesting a role of 11-KT in ED differentiation during sex change. There were no basic differences in the mechanisms of natural and artificially induced ED differentiation. Two types of structure led to the formation of EDs in two different areas of the newly formed testis during sex change. (c) 2007 The Authors.
Abstract: 11-ketotestosterone (11-KT), a potent male-specific androgen in fish, has important roles on spermatogenesis, male behavior, and nuptial coloration. The site of 11-KT synthesis and its role on male germ cell development during protogynous sex change is not clearly understood. We examined the dynamics of steroidogenic enzymes immunolocalization, viz cholesterol side-chain cleavage (P450scc), biomarker of steroids and cytochrome P45011 beta-hydroxylase (P45011 beta), downstream to 11-KT production, throughout the process of sex change in honeycomb grouper (Epinephelus merra). In female, P450scc immunoreactivity (-ir) was observed in the theca layer and tunica near blood vessels (BV). During the onset of sex change, P450scc reactive cells were observed in the remaining follicle layer of degenerated oocyte of the ovo-testis in early transitional (ET) and late transitional (LT). In male, P450scc-ir was localized in the interstitial Legdig cells of testis. P45011 beta reactive cells were observed in the tunica near BV in female but not in theca layer. In ET and LT phases gonads P45011 beta localized in remaining follicle layer of degenerated oocyte and tunica near BV. On the other hand, in male, both interstices and tunica near BV showed strong signals against P45011 beta. Moreover, in vivo and in vitro levels of 11-KT related with the changes in the nuclei diameter of P45011 beta-positive cells in both tunica near BV and remaining follicle layer of degenerated oocyte to interstices during the progress of sex change. The present results suggest that 11-KT produced in the tunica near BV may provide the stimulus for female to degenerate oocytes and initiate sex change. However, 11-KT produced both in tunica near BV and remaining follicle layer of degenerated oocyte possibly plays critical role during testicular differentiation as well as gonadal restructuring at mid to late phases (ET to LT) of sex change in honeycomb grouper.
Abstract: 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. (c) 2006 Elsevier B.V All rights reserved.
Abstract: The honeycomb grouper, Epinephelus merra, is a protogynous hermaphrodite fish. Sex steroid hormones play key roles in sex change of this species. A significant drop in endogenous estradiol-17 beta (E2) levels alone triggers female-to-male sex change, and the subsequent elevation of 11-ketotestosterone (11KT) levels correlates with the progression of spermatogenesis. To elucidate the role of an androgen in sex change, we attempted to induce female-to-male sex change by exogenous 11KT treatments. The 75-day 11KT treatment caused 100% masculinization of pre-spawning females. Ovaries of the control (vehicle-treated) fish had oocytes at various stages of oogenesis, while the gonads of the 11KT-treated fish had transformed into testes; these contained spermatogenic germ cells at various stages, including an accumulation of spermatozoa in the sperm duct. In the sex-changed fish, plasma levels of E2 were significantly low, while both testosterone (T) and 11KT were significantly increased. Our results suggest that 11KT plays an important role in sex change in the honeycomb grouper. Whether the mechanism of 11 KT-Induced female-to-male sex change acts through direct stimulation of spermatogenesis in the ovary or via the inhibition of estrogen synthesis remains to be clarified.
Abstract: Circulating estradiol-17 beta (E2) levels decrease precipitously during female to male (protogynous) sex change in fish. Whether this drop in E2 levels is a cause or consequence of sex change is still largely unknown. The present study treated adult female honeycomb groupers (Epinephelus merra) with aromatase inhibitor (AI, Fadrozole), either alone or in combination with E2, to investigate the role of estrogen in protogynous sex change. Control fish had ovaries undergoing active vitellogenesis; the gonads of AI-treated fish had already developed into testes, which produced sperm capable of fertilization. In contrast, co-treatment of fish with E2 completely blocked AI-induced sex reversal. AI treatment significantly reduced circulating levels of E2, whereas the addition of E2 to AI prevented the loss. The plasma androgen (testosterone and 11-ketotestosterone) levels were increased in the AI-treated fish, while the levels in the E2-supplemented fish were low compared to controls. Present results show that E2 plays an important role in maintaining female sex of hermaphrodite fishes, and that the inhibition of E2 synthesis causes oocyte degeneration leading to testicular differentiation in the ovary. (c) 2005 Wiley-Liss, Inc.
Abstract: Androgen plays an important role in the developing ovaries of female fish. However, little is known regarding either the sites of production of androgen or its functional roles. In the present study, we investigated immunohistochemically the localization of cholesterol-side-chain-cleavage (P450scc) and cytochrome P45011 beta-hydroxylase (P45011 beta) with antibodies P450scc and P45011 beta in the ovary of the female honeycomb grouper Epinephelus merra during its reproductive cycle. Clusters of strongly immunopositive cells, with 100-1000 cells in each cluster, against both P450scc and P45011 beta, were observed throughout the annual reproductive cycle in tissue near blood vessels in the tunica ovary surrounding the outer periphery of the ovary. The ultrastructural characteristics of these cells showed that they were steroid-producing cells. In contrast, immunopositive cells against P450scc but not against P45011 beta were localized in the theca layer surrounding the outer periphery of oocytes. These results suggest that two distinct steroid biosynthesis sites exist in the ovary and that cells at the two sites differ functionally. The only cells that biosynthesize 11-ketotestosterone are found in clusters in the vicinity of blood vessels; they possibly play a physiological role in oocyte growth and gonadal restructuring during the sex change of individuals of this species.
