Morphological markers to select populations of oocytes with different cultural needs for dedicated pre-maturation systems

Introduction Several studies support the notion that in vitro pre-maturation treatments aimed to improve the developmental capability of immature oocytes have a different effect depending on the oocyte metabolic status at the time of its removal from the follicle. We demonstrated that changes in large-scale chromatin configuration within the germinal vesicle (GV) of fully-grown bovine oocytes are related to the acquisition of developmental competence. In particular, only a limited percentage of GV1 oocytes reached the blastocyst stage, while GV2 and GV3 oocytes showed a higher embryonic developmental potential. The present study aimed at identifying possible correlations between cumulus-oocyte complex (COC) morphology and chromatin configurations. Methods COCs were collected from 2-6mm follicles, selected according to commonly accepted criteria for in vitro embryo production and those with evident signs of atresia were discarded. Selected COCs were further divided into 3 groups based on the texture of the ooplasm (homogenous or granulated) and on the morphology of the cumulus oophorus (layers number, degree of expansion of outer layer). After cumulus cell removal, chromatin configuration was assessed by DAPI staining. Results and Discussion Our study indicate that GV1 is present only in group 1 (homogenous ooplasm and absence of outer layer expansion), representing one third of group 1 total COCs, while group 2 and 3 are similarly enriched of GV2 and GV3. This can provide a non-invasive approach to select populations of oocytes with different cultural needs to be subjected to dedicated in vitro development protocols. This hypothesis is currently under investigation.