Molecular evaluation of oocyte maturation and use of cytoplasmic transfer to increse oocyte competence of repeat breeder dairy cows

Abstract

Repeat breeder (RB) cows are defined as animal with subfertility that do not become pregnant even after many services. Its incidence is quite variable, averaging 14%, causing large economic loss. Although studies indicate RB may have a lack of oocyte competence, it is still unclear why these cows become RB and which molecular alterations are related to this syndrome. Recently, reduced number of copies of mitochondrial DNA was associated to reduced blastocyst rate when oocytes where retrieved from RB cows under heat stress and fertilized in vitro. Moreover, traces of the activation of pro-apoptotic mechanisms (greater expression of ITM2B and Bax/Bcl2) and compensatory mechanisms of the mitochondrial function deficiency (greater expression of PPARG, POLG, POLG2 and TFAM) were evidenced. Several other mechanisms may be related to the reduction of oocyte competence of RB cows. The study of the expression of local factors secreted by the oocyte that are essential to control an adequate maturation (i.e. GDF9, BMP15 and FGFs, for example), may be an important step to help the understanding oocyte disruption of RB cows. One of the great challenges that remain in the field of reproductive biology, retarding the creation of new strategies, is the understanding of the nature of the molecular and cellular processes that control oocyte quality. Thus, aiming to improve the understanding of the molecular basis related to reduced oocyte quality of RB cows, and to improve these oocytes competence to develop into blastocysts it is proposed herein: (1) the investigation of the expression of target transcripts (GDF9, BMP15, FGF8, FGF10, FGF16 and FGF17) associated to oocyte maturation of RB cows and (2) the use of cytoplasmic transfer from heifers zygotes to RB zygotes to evaluate its efficiency to improve the competence to develop into blastocyst of the receptor oocytes. Hence, this research goal is to better understand the extension of the molecular alteration and to establish a possible therapy to overcome the fertility problems of RB cows. (AU)