NEW BIOTECHNOLOGIES IN ANIMAL PRODUCTION AND REPRODUCTION

Coordinator: Mônica Rodrigues Ferreira Machado

Among the approximately 24,000 species of fish found in rivers and oceans, 96% of them are teleosts. These individuals present different reproductive strategies that include tactics such as: hermaphroditism, courtship and mating, and migration. However, with the construction of hydroelectric plants, urbanization, agriculture, and the introduction of exotic species, there has been a decline in natural stocks, and the production of breeding stocks has become increasingly necessary. To this end, it is also necessary for these breeding stocks to have adequate feeding management that promotes both growth and increased precocity and prolificacy. Among fish, there are different types of follicular and oocyte growth. Thus, we can mention fish with total and partial spawning. Fish with partial spawning present asynchronous follicular growth, having different types of follicles present in their ovary. Fish that spawn completely have only one follicle size in their ovaries, and all of them are ovulated at the same time. This variation in follicular dynamics also influences metabolism during the reproductive process, with fish that spawn partially reproducing throughout the year, while fish that spawn completely reproducing only once during the year. Most fish that spawn completely migrate and are not able to spawn in lentic environments. Therefore, artificially manipulating their cycle to induce spawning allows these individuals to reproduce at the desired time and under controlled conditions. The reproductive cycle in fish is divided into two phases: first, the proliferation, growth and differentiation of gametes (spermatogenesis and vitellogenesis) occurs. Then, the maturation and extrusion of oocytes and spermatozoa and insemination occur. These events are coordinated by the hypothalamic-pituitary-gonadal axis, which, after processing external and internal stimuli, initiates the release of gonadotropin-releasing hormone (GnRH). These events are inhibited by dopamine, and knowledge about fish reproductive endocrinology is of great practical importance in induced reproduction in fish. The hypothalamic-pituitary system is responsible for the initiation of folliculogenesis. Initially, gonadotropin-releasing hormone (GnRH) is released, which determines the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), while dopamine inhibits them. Using primary culture of tilapia pituitary glands, it was observed that when stimulated with sGnRH, there is an increase in ERK1/2 phosphorylation, promoting phosphorylation of PKC, which in turn determines an increase in the expression of growth hormone (GH) and luteinizing hormone (LH), but not of follicle-stimulating hormone (FSH). The increase in FSH is also determined by GnRH, but via an increase in cAMP-PKA. Dopamine acts directly on the pituitary gland, inhibiting the expression of GnRH receptors. It also inhibits the synthesis and release of GnRH in the hypothalamus and the induction of the release of pituitary gonadotropins induced by this hormone. In this way, dopamine functions as a physiological antagonist of GnRH, both at the pituitary and hypothalamic levels. FSH synthesized by the pituitary gland is responsible for the conversion of testosterone produced by the follicular thecal cells into estradiol in the granulosa cells, which is subsequently secreted into the blood. This increase in estrogen levels promotes both the incorporation of vitellogenin by the pre-vitellogenic follicles and the synthesis of the M-phase promoting factor (MPF) by the follicles, which is responsible for oocyte maturation, determining the resumption of meiosis and germinal vesicle breakdown (GVBD), chromosome condensation, formation of the meiotic spindle, and progression to phase II of meiosis. Another hormone that induces MPF is anti-mullerian hormone (MIH), which is synthesized during the final phase of oocyte maturation. MIH stimulates the production of 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17α, 20β-DP), which is associated with 17α, 20β-DP for the formation of maturation-stimulating steroids (MIS) by granulosa and theca cells. Gonadotropins stimulate the production of 17 alpha hydroxyprogesterone, which is later converted to 17α, 20β-DP by follicular cells. The high concentrations of MIS during the final phase of oocyte maturation are due to the decrease in the aromatase enzyme. If we take into account steroidogenesis, the precursor of steroids is pregnenolone, formed from arachidonic acid that will be converted to progesterone (P4) and can later be metabolized into 17-hydroxy progesterone (17P4) by 17α hydroxylase (CYP17). 17P4 is later converted into androstenedione (AD) by C17,20 lyase (CYP17) or into 17α,20β-dihydroxyprogesterone (17α,20β-DP) by 20β hydroxysteroid dehydrogenase (20β-HSD). 17α,20β-