Growth differentiation factor 9 and bone morphogenetic protein 15 expression in previtellogenic oocytes and during early embryonic development of Yellow-tail Kingfish Seriola lalandi.

Jaime Palomino,Giannina Herrera,Víctor Martínez,Phillip Dettleff

doi:10.1186/0717-6287-47-60

Abstract

BackgroundDuring fish oocyte maturation, specific molecules are expressed and accumulated within oocyte until fertilization and embryo development. Special attention have been paid in members of the transforming growth factor (TGF-β) superfamily; growth differentiation factor 9 (GDF9/gdf9) and bone morphogenetic protein 15 (BMP15/bmp15), which exert regulatory functions during oocyte maturation and follicle development. However, little attention has been paid to the involvement of these molecules during embryogenesis considering its importance for the formation of a good quality egg and subsequent embryo survival. The purpose of this study was to analyze the expression of gdf9 and bmp15 in previtellogenic oocytes and during early embryonic development in Seriola lalandi, a pelagic fish with increasing prospect for its aquaculture development, which however, show high mortality at embryo and larval stages.ResultsThrough RT-qPCR it was found that gdf9 expression was higher in previtellogenic oocytes decreasing after ovulation. This expression profile agrees with its participation in early stages of the follicular development. The transcripts for bmp15 also showed the highest levels in previtellogenic oocytes, however this expression was lower than obtained with gdf9. Conversely, in recently spawned oocytes mRNA bmp15 levels were highest than observed to gdf9. This, is consequent with the main role proposed for this growth factor at the final fish oocyte maturation: avoid the ovulation of an immature oocyte. During embryo development, low levels of mRNA were detected to gdf9, with an increase in 48 H post-fertilization embryos. The bmp15 expression did not change throughout development and was higher than gdf9 at 16 cells, blastula and appearance embryos stages.ConclusionsBoth (gdf9 and bmp15) expression profiles in previtellogenic oocytes and newly spawned eggs are consistent with the described functions for these growth factors in vertebrate ovarian physiology in early and late stages of the follicular development. So, these genes could be considered as quality biomarkers at these stages. However, further studies of these proteins throughout folliculogenesis, are necessaries to fully understand their functions during the oocyte formation. In addition, the persistent expression of these growth factors during development, allows us to speculate possible roles in embryonic processes, which must also be addressed.

Highlights

During fish oocyte maturation, specific molecules are expressed and accumulated within oocyte until fertilization and embryo development
This, is consequent with the main role proposed for this growth factor at the final fish oocyte maturation: avoid the ovulation of an immature oocyte
Both expression profiles in previtellogenic oocytes and newly spawned eggs are consistent with the described functions for these growth factors in vertebrate ovarian physiology in early and late stages of the follicular development

Summary

Introduction

Specific molecules are expressed and accumulated within oocyte until fertilization and embryo development. Evidence regarding to the active role of the oocyte in its maturation during folliculogenesis and the effect on embryonic development, has been accumulated [1,2] This role is performed through molecules secreted by the oocyte which could regulate the folliculogenesis and steroidogenesis in both granulose and theca cells [3]. Some of the key molecules involved in these processes are the members of the transforming growth factor β super family (TGF-β), GDF9 and BMP15 [4,5] These growth factors stimulate the proliferation of granulose cells, and suppress follicle stimulating hormone (FSH)-induced granulose cell differentiation [6,7]. It has been purposed that BMP-5 participate in the regulation of cumulus cell apoptosis, but the molecular mechanism it is still unknown [13]

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