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Basic reproductive biology

A significant amount of the research programme of the EABRG is focused on understanding the mechanisms controlling sexual development and reproduction in fish. This work provides a fundamental underpinning for much of our research on endocrine disruption and other chemical effects measures.

Major research activities and findings under this theme include:

Sexual differentiation. We have established the timing and mapped histologically the process of sexual differentiation in the roach, Rutilus rutilus, a sentinel species for studies on chemical effects in wild fish in UK freshwaters, and in the fathead minnow and zebrafish, both key laboratory species. We are actively studying the molecular mechanisms controlling sexual differentiation in these fish and have identified suites of genes involved with this process.

Oogenesis (egg development) and Spermatogenesis. We have mapped histologically the process of oogenesis and spermatogenesis in roach, fathead minnow and zebrafish. In this work we have especially focused on the process of vitellogenesis (provision and uptake of yolk into oocytes) and established some of the endocrine and molecular mechanisms controlling yolk uptake and processing. Our work has included the cloning and sequencing of the first cDNA for a fish vitellogenin receptor, establishing the developmental expression and cellular localisation of the vitellogenin receptor mRNA in fish oocytes, and the cloning and sequencing of some of the first yolk processing enzymes (cathepsins) in oocytes. We also developed some of the first assays to quantify vitellogenins in fish, which have been vital for our work (and other laboratories worldwide) on endocrine disruption.

Endocrine control of fecundity. Very little is known about the determinants of fecundity in any animal. Fish, because they are highly fecund, provide excellent model systems for investigating the endocrine control of oocyte recruitment and growth - the associated titres of plasma hormones are considerably higher than for most other animals. We have applied the technique of unilateral ovariectomy (to manipulate oocyte recruitment) to identifiy some of the hormones control ling ovarian development. In this work, an assay we developed for follicle stimulation hormone (FSH) in trout has been used effectively to determine the effects of endocrine active chemicals on pituitary function.

Puberty. Recently in mammals a novel pituitary receptor, KiSS I receptor and its associated ligands (KiSS peptins) have been cloned and shown to play key roles in initiating puberty. We have a project researching into the mechanisms controlling puberty in fish. To date we have cloned the KiSS I receptor in various fish species, identified and cloned some of the KiSS peptin ligands (the first to do so in fish) and mapped them to their chromosomes. We have established the ontogeny and localization of expression of KiSS 1 receptor in the brain in both male and female fathead minnow during sexual development and shown how this expression aligns with the expression of an extensive suite if other genes involved in mediating sexual development (e.g. the GnRHs). The ability to control puberty in fish would be of great significance in the aquaculutre of many fish species. Our work on puberty includes how endocrine active chemicals in the environment may alter the timing of puberty in wild fish populations.

Sexual behaviour. The zebrafish is one of the major models for studies in ecotoxicology, yet very little is known about its basic biology. We have contributed to filling this knowledge gap through extensive studies on its reproductive biology. In this work we have projects studying the behaviour of the zebrafish in breeding colonies. This work is principally focused on understanding the interactions and hierarchies that develop in zebrafish colonies to advance our understanding on their breeding dynamics in natural populations. In this work, detailed studies on male-male, male-female and female-female interactions are being established for different sized colonies and the reproductive success of individuals in those colonies are determined through genotyping of the offspring produced (through the use of DNA microsatellites). Our work on zebrafish is principally laboratory based, but we also have some ongoing studies on natural colonies in Pakistan. This work also includes the development and application of population models. Working with colleagues in the School of Biosciences at Exeter (Dr Wilson) we are also studying the interactions between behaviour, social hierarchy the endocrinology of Atlantic salmon.