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Identification of Novel Bovine Cumulus Cell Molecular Markers Predictive of Oocyte Competence: Functional and Diagnostic Implications¹

Laboratory of Mammalian Reproductive Biology and Genomics³ and Departments of Animal Science⁴ and Physiology,⁵ Michigan State University, East Lansing, Michigan 48824 Division of Animal and Nutritional Sciences,⁶ West Virginia University, Morgantown, West Virginia 26506

ABSTRACT

The present study was undertaken to discover molecular markers in bovine cumulus cells predictive of oocyte competence and to elucidate their functional significance. Differences in RNA transcript abundance in cumulus cells harvested from oocytes of adult versus prepubertal animals (a model of poor oocyte quality) were identified by microarray analysis. Four genes of interest encoding for the lysosomal cysteine proteinases cathepsins B, S, K, and Z and displaying greater transcript abundance in cumulus cells surrounding oocytes harvested from prepubertal animals were chosen for further investigation. Greater mRNA abundance for such genes in cumulus cells of prepubertal oocytes was confirmed by real-time RT-PCR. Elevated transcript abundance for cathepsins B, S, and Z also was observed in cumulus cells surrounding adult metaphase II oocytes that developed to the blastocyst stage at a low percentage following parthenogenetic activation versus those that developed at a high percentage. Functional significance of cumulus cell cathepsin expression to oocyte competence was confirmed by treatment of cumulus-oocyte complexes during in vitro oocyte maturation with a cell-permeable cysteine proteinase (cathepsin) inhibitor. Inhibitor treatment decreased apoptotic nuclei in the cumulus layer and enhanced development of parthenogenetically activated and in vitro-fertilized adult oocytes to the blastocyst stage. Stimulatory effects of inhibitor treatment during meiotic maturation on subsequent embryonic development were not observed when oocytes were matured in the absence of cumulus cells. The present results support a functional role for cumulus cell cathepsins in compromised oocyte competence and suggest that cumulus cell cathepsin mRNA abundance may be predictive of oocyte quality.

apoptosis, assisted reproductive technology, cathepsins, cumulus cells, embryo, oocyte quality

¹Supported by funding from the Michigan State University Reproductive and Developmental Sciences Program, the Michigan Agricultural Experiment Station, and the Rackham Foundation to G.W.S. Microarray data can be accessed via Gene Expression Omnibus (accession no. GSE10809).

Correspondence: ²George W. Smith, 1230 Anthony Hall, Michigan State University, East Lansing, MI 48824. FAX: 517 353 1699; e-mail: smithge7{at}msu.edu

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