Yonathan Zohar, Ph.D.
Laboratory of Fish Reproductive Endocrinology
This laboratory studies the hormonal regulation of gametogenesis and final oocyte maturation, ovulation and spawning in fish. Our primary models are commercially important farmed fish, including striped bass and seabream. Endocrine, biochemical and molecular approaches are used in the laboratory. Special emphasis is given to studying vertebrate gonadotropin-releasing hormones (GnRH), their nature, mechanisms of actions, and regulation of synthesis and release. We have recently discovered a new form of GnRH, seabream GnRH (sbGnRH) and have demonstrated that the brain of many evolved fish contains three forms of GnRH: salmon GnRH (sGnRH), chicken GnRH II (cGnRH II) and sbGnRH. We have shown that sbGnRH is the most abundant form in the pituitary of sexually mature fish. We are studying the endocrine functions of the three forms of GnRH in striped bass and seabream. Our goal is to understand their relative roles in inducing gonadotropin release and in the processes of puberty, oogenesis and spermatogenesis. We have cloned the genes and cDNA of the three forms of GnRH present in striped bass and seabream brains and are studying the pattern of expression of the genes coding each of the three forms. This includes studies on the regulation of the expression of each of the three GnRH genes by environmental and endocrine factors. A specific focus is on the promoter region of the fish GnRH genes, to determine which hormonal factors regulate their expression. Based on our basic research, this laboratory develops technologies for the exogenous manipulation of fish reproduction to be used in the aquaculture industry. We have demonstrated that the absence of final oocyte maturation, ovulation and spawning in many farmed fish is the result of a lack of gonadotropin release. We have thus developed a GnRH based therapy to induce farmed fish to spawn in captivity. We combine the hormonal treatment with environmental manipulations to obtain spawning all year round. Another important area of research in this lab is the endocrine control of the onset of puberty. We are presently developing a combined GnRH and steroid treatment to induce precocious puberty in fish that reach sexual maturity at a late age. Our laboratory at the Columbus Center contains all the necessary equipment for the endocrine and the molecular work, as well as a state of the art Aquaculture Research Center for holding and studying fish.
Recent Publications
Zohar Y, Elizur A, Sherwood NM, Rivier JF, Zmora N 1995 Gonadotropin-releasing potencies of the three native forms of gonadotropin-releasing hormones present in the brain of gilthead seabream, Sparus aurata. Gen Comp Endocrinol 97:289-299.
Gothilf Y, Munoz-Cueto JA, Sagrillo CA, Selmanoff M, Chen TT, Kah O, Elizur A, Zohar Y 1996 Three forms of gonadotropin-releasing hormone in a perciform fish (Sparus aurata): cDNA characterization and brain localization. Biol Repro 55:636-645.
Mylonas CC, Scott AP, Vermeirssen ELM, Zohar Y 1997 Changes in plasma gonadotropin II and sex-steroid hormones, and sperm production of striped bass after treatment with controlled-release GnRHa-delivery system. Biol Reprod 57:669-675.
Gothilf Y, Meiri I, Elizur A, Zohar Y 1997 Changes in mRNA levels of the three GnRH forms during final oocyte maturation, ovulation and spawning in the gilthead seabream, Sparus aurata. Biol Repro 57:1145-1154.
