Maturation conditions do not affect Myst1, Hat1 and Sirt1 mRNA abundance in horse oocytes

Introduction We recently demonstrated that in vitro maturation (IVM) is associated with defects in histone H4 lysine 16 (H4K16) acetylation in horse oocytes, together with a higher incidence of spindle anomalies and aneuploidy. In the present study we investigated whether maturation conditions can alter the abundance of transcripts involved in histone acetylation and deacetylation. The specific H4K16 acetyl-transferase Myst1, the general acetyl-transferase Hat1 and the specific H4K16 deacetylase Sirt1 were examined in GV-stage oocytes and after in vivo maturation or IVM. Methods Follicle growth was followed by daily ultrasound scanning in adult mares. When a follicle >33mm emerged, hCG was injected. After 35h the in vivo mature oocyte was collected by ultrasound-guided transvaginal aspiration. For IVM, oocytes were collected from follicles 5-25mm and cultured for 28h with EGF and serum. GV-stage oocytes and follicular cell samples were also collected from follicles 5-25mm. Samples were retro-transcribed using random hexamers and analyzed by real-time Q-PCR. Gapdh and Renilla Luciferase served as internal and external housekeeping, respectively. Results and Discussion Our study reports for the first time the expression of Hat1, Myst1 and Sirt1 in horse oocytes and follicular cells. Hat1, Myst1 and Sirt1 were expressed at the same extent in GV-stage oocytes and after maturation, independently from the maturation conditions. Our findings show that the transcript abundance of Hat1, Myst1 and Sirt1 does not decrease during horse oocyte maturation, strongly suggesting that IVM does not promote/accelerate the degradation of transcripts, but rather affects H4K16 acetylation machinery at translational or post-translational level. (L’Oreal2012)