Ovary

High Transcript Level of Fatty Acid-Binding Protein 11 But Not of Very Low-Density Lipoprotein Receptor Is Correlated to Ovarian Follicle Atresia in a Teleost Fish (Solea senegalensis)

Abstract
Transcripts encoding a fatty acid-binding protein (FABP), Fabp11, and two isoforms of very low-density lipoprotein receptor (Vldlr) (vitellogenin receptor) were characterized from the ovary of Senegalese sole (Solea senegalensis). Phylogenetic analyses of vertebrate FABPs demonstrated that Senegalese sole Fabp11, as zebrafish (Danio rerio) homologous sequences, was part of a newly defined teleost fish FABP subfamily which was a sister clade of tetrapod FABP4/FABP5/FABP8/FABP9. Reverse transcriptase polymerase chain reaction (RT-PCR) revealed high levels of vldlr transcript splicing variants in the ovaries and, to a lesser extent, in somatic tissues, while fabp11 was highly expressed in the ovaries, liver, and adipose tissue. In situ hybridization analysis showed vldlr and fabp11 mRNAs in previtellogenic oocytes, while no hybridization signals were detected in the larger vitellogenic oocytes. fabp11 transcript expression was strongly up-regulated in somatic cells surrounding atretic follicles. Real-time quantitative RT-PCR demonstrated that ovarian transcript levels of vldlr and fabp11 had a significant positive correlation with the percentage of follicles in previtellogenesis and atresia, respectively. These results suggest that the expression level of vldlr transcripts may be used as a precocious functional marker to quantify the number of oocytes recruited for vitellogenesis and that fabp11 mRNA may be a very useful molecular marker for determining cellular events and environmental factors that regulate follicular atresia in fish.

Key words: Ovary • Follicular development • Gametogenesis • Gene regulation • Oocyte development