Abstract
BackgroundThe full maturational capability of mammalian oocytes is accompanied by nuclear and cytoplasmic modifications, which are associated with proliferation and differentiation of surrounding cumulus cells. These events are regulated on molecular level by the expression of target genes involved in signal transduction pathways crucial for folliculogenesis and oogenesis. Transforming growth factor beta signaling includes several molecules that are involved in the regulation of oogenesis and embryo growth, including bone morphogenetic protein (BMP). However, the BMP-related gene expression profile in oocytes at different maturational stages requires further investigation.MethodsOocytes were isolated from pubertal crossbred Landrace gilts follicles, selected with a use of BCB staining test and analyzed before and after in vitro maturation. Gene expression profiles were examined using an Affymetrix microarray approach and validated by RT-qPCR. Database for Annotation, Visualization, and Integrated Discovery (DAVID) software was used for the extraction of the genes belonging to a BMP-signaling pathway ontology group.ResultsThe assay revealed 12,258 different transcripts in porcine oocytes, among which 379 genes were down-regulated and 40 were up-regulated. The DAVID database indicated a “BMP signaling pathway” ontology group, which was significantly regulated in both groups of oocytes. We discovered five up-regulated genes in oocytes before versus after in vitro maturation (IVM): chordin-like 1 (CHRDL1), follistatin (FST), transforming growth factor-beta receptor-type III (TGFβR3), decapentaplegic homolog 4 (SMAD4), and inhibitor of DNA binding 1 (ID1).ConclusionsIncreased expression of CHRDL1, FST, TGFβR3, SMAD4, and ID1 transcripts before IVM suggested a subordinate role of the BMP signaling pathway in porcine oocyte maturational competence. Conversely, it is postulated that these genes are involved in early stages of folliculogenesis and oogenesis regulation in pigs, since in oocytes before IVM increased expression was observed.
Highlights
The full maturational capability of mammalian oocytes is accompanied by nuclear and cytoplasmic modifications, which are associated with proliferation and differentiation of surrounding cumulus cells
The set of genes consisting of chordin-like 1 (CHRDL1), FST, TGFβR3, SMAD4, and inhibitor of DNA binding 1 (ID1) was subjected to hierarchical clusterization procedure and presented as a heatmap
The set of differentially expressed genes belonging to “bone morphogenetic protein (BMP) signaling pathway” GO Gene ontology biological process group (BP) term category is presented in Table 2 where their symbols, names, fold changes, and corrected p-values are shown
Summary
The full maturational capability of mammalian oocytes is accompanied by nuclear and cytoplasmic modifications, which are associated with proliferation and differentiation of surrounding cumulus cells. These events are regulated on molecular level by the expression of target genes involved in signal transduction pathways crucial for folliculogenesis and oogenesis. The mammalian cumulus-oocyte complexes (COCs) undergo growth, as well as substantial morphological and biochemical differentiation, during the long stages of folliculogenesis and oogenesis [1]. The biochemical changes include nuclear and cytoplasmic maturation of the oocyte and formation of gap junction connections (GJCs) between the gamete and surrounding somatic cells, which are associated with the bi-directional transport of small substances [2, 3]. Some differentially expressed genes may be recognized as new markers of maturational competence [5]
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