Regassa et al. BMC Genomics 2011, 12:57 http://www.biomedcentral.com/1471-2164/12/57 important for oocyte growth and maturation and granu- losa cells proliferation [85]. Although a number of genes were differentially expressed between CCs that were cultured with or with- out their enclosed oocytes, it is not easy to conclude that removal of oocyte completely changes the expres- sion of CCs genes at MII stage. For instance, except HAS2, the majority of CCs genes previously identified as molecular bio markers for developmental competence including INHbA, EGFR, BTC, CD44, TNFAIP6, PTX3 and PTGS2 [40,48] were not differentially expressed between the two sample groups. From these results, we hypothesize that either these differentially expressed genes predict oocyte developmental competence better than the previously indentified ones or the transcription of these previously identified genes is completed earlier at GV stage before the ooplasm is removed and hence they are not differentially expression at MII stage. How- ever, the assertion of both hypotheses requires further investigation. The dynamics of CCs transcriptome during the transition of COCs from GV to MII stages is associated with functional changes Massive transcript degradation during in vitro matura- tion of bovine [86], human [42,59] and mouse [59] oocytes has been reported. Similarly, considerable shift of transcripts and associated functional changes were observed in CCs during the transition of COCs from GV to MII stage. For instance, while transcripts that are involved in cell cycle, DNA replication, metabolic process, steroid and cholesterol biosynthesis, signal transduction and regulation of catalytic activity are over expressed in CCs at GV stage, these involved in cell adhesion, protein metabolic process, regulation of cellular component organization and biogenesis and actin filament polymerization are over expressed in CCs at MII stage (Figure 13). The most interesting finding of this experiment is not only the change in the number of transcripts but also the identity of tran- scripts that are involved in a given GO term at the two developmental stages. Cell cycle and DNA replication are the two successive events which play significant roles in meiotic process resulting in the formation of four haploid cells. The functioning of a cell depends upon its ability to extract and use chemical energy stored in organic molecules via metabolic pathways. On the other hand, MAPK activa- tion in CCs rather than in oocytes exerts essential func- tions during mammalian oocyte meiotic resumption [66,87] and steroids such as progesterone have been suggested to induce cAMP dependent MAPK signaling cascade leading to meiotic resumption [88]. Hence, over expression of transcripts that are involved in cell cycle, Page 16 of 20 metabolic and steroid biosynthetic pathways in CCs at GV stage suggest that these pathways are more active in GV than in MII stage. As the oocyte lacks gonadotropin receptors, it has been hypothesized that FSH exerts its effect via a posi- tive meiosis factor (EGF) synthesized by CCs indirectly via signal transduction pathway that involves cAMP dependent MAPK to induce meiotic resumption [89]. From these findings, we propose that over expression of transcripts that are involved in signal transduction path- way at GV stage CCs relative to MII is an indication that this pathway is more active at the former than the latter. Focal adhesions are large macromolecular assemblies through which both mechanical force and regulatory signals are transmitted [90]. They serve not only to anchor the cell, but also to carry signals, which inform the cell about the condition of the ECM and thus affect their behaviour [91]. In view of their increased expres- sion at MII relative to their expression at GV stage, we propose that these genes are involved in one of the reg- ulatory network that connects the oocyte to its compa- nion CCs during in vitro maturation. Actin filaments localize to specific regions within mammalian oocytes and their modelling including poly- merization are important for oocyte maturation, fertili- zation and embryo development [76,92,93]. Interestingly, we found higher expression of transcripts that are involved in actin filament polymerization at MII than in GV CCs. Consistent with the notion that in vitro meio- tic resumption in bovine oocytes is triggered by FSH [76,93]; we observed higher expression of FSHR mRNA in GV CCs than in MII stage. Prior to in vitro meiotic resumption, FSH is received by CGCs via FSHR and this activates the release of cAMP and MAPK signaling pathways to initiate meiotic resumption [88]. CCs expansion is a key biological event for successful oocyte maturation, ovulation and fertility [40,48,94,95]. HAS2 is an important enzyme for the biosynthesis of HA to form stable matrix during CCs expansion [96]. The binding proteins of HA (TNFAIP6 and PTX3) and its receptor protein (CD44) plays significant roles in attaining full CC expansion. CD44 is a widely expressed cell adhe- sion molecule that binds the extracellular matrix compo- nent, HA in a tightly regulated manner [97]. The interaction between HA and CD44 is the key molecular mechanism for the activation of signalling cascades that contribute to cell adhesion, proliferation, migration and differentiation [98,99]. This interaction is also important for MAPK signalling pathway in oocyte and may promote meiotic resumption [100]. Oocytes can’t attain cytoplasmic maturation when cultured in the absence of their compa- nion CCs as they can’t store sufficient mRNAs, proteins and transcription factors that are important for maturation