Regassa et al. BMC Genomics 2011, 12:57 http://www.biomedcentral.com/1471-2164/12/57 Page 14 of 20 Figure 21 Immunoflourescence images taken from sections of ovarian follicles showing the protein of IRF6 expressed only in oocytes and that of MSX1 expressed in both oocyte and CCs. Lanes A and E. = ovarian sections incubated with IRF6 and MSX1 primary antibodies showing the location of IRF6 and MSX1 proteins, respectively. B and F = Protein and nuclear staining showing IRF6 and MSX1 proteins and DNAs together. C = Sections incubated only with DAPI showing the nucleus of the cells D. Negative control staining in which the sections were incubated only with secondary antibodies. The red arrows indicate the location of each protein. Scale bars below each picture represent 20 μm. are shown in Figure 20. Previous studies have suggested that higher expression of HAS2, PTX3, TNFAIP6, PTGS2, CD44, INHBA and BTC in CCs can be used as molecular bio-markers to select quality embryo in women [40] and cow [48]. Higher expression of PTX3, PTGS2, ADAMTS1, INHA and INHBA was also reported in human CCs [42]. But, data that clearly demonstrate whether these transcripts are oocyte or CC specific or expressed in both is not available. Here, we show that none of HAS2, PTX3, INHA, INHBA and CD44 are CC specific as they are expressed in both samples (supple- mental tables S3 and S6, Figure 20). Additionally, we report for the first time that POU class 5 homeobox 1 (POU5F1), interferon regulatory fac- tor 6 (IRF6), sex determining region Y box2 (SOX2) and insulin like growth factor 2 binding protein 3 (IGF2BP3) are expressed only in oocytes while secreted protein, acidic, cysteine-rich (SPARC), glutamate pyruvate transa- minase (GPT), ADAM metallopeptidase with thrombos- pondin type 1 (ADAMTS1) and heparanase (HPSE) are expressed only in CCs. Significantly higher expression of POU5F1 has been reported in developmentally compe- tent bovine oocytes and its loss of function has resulted in preimplantation lethality in mouse embryos as it is a central regulator of pluripotency [69]. Similarly, SOX2, which is expressed only in oocyte, is a developmental pluripotency marker and has been hypothesized as a regulator of POU5F1 controlled genes [70] suggesting a possible synergetic effect of the two genes on oocyte maturation. IRF6 has been suggested as a key mediator of cellular proliferation and differentiation in mammary epithelial cells by facilitating entry into the G0 phase of the cell cycle [71]. It regulates cell proliferation and differentia- tion in different cell types and its higher expression in oocyte sample in the present study at both mRNA and protein levels (Figure 21) may show IRF6 as a maternal candidate transcript that play a role in acquiring devel- opmental competence. ADAMTS1 is also expressed only in CCs but more abundantly at MII compared to at GV stage (Figure 20). Previously, increased expression of ADAMTS1 protein has been reported in mouse GCs in response to preovulatory LH surge [72] where it targets Versican (VCAN), one of the proteins that cross link hyaluronic acid (HA) rich CCs matrix and contributes to oocyte maturation, ovulation and/or fertilization [73]. Transcripts specifically expressed in CCs also include SPARC, a multifunctional calcium-binding glycoprotein that modulates extracellular matrix interactions and influences cell-cell adhesion, migration and invasion in vitro and in vivo [74]. Although the role of SPARC in the biology of oocytes is not documented, the fact that it is expressed only CCs supports previous reports where it has been expressed only in the somatic cells of germarium and follicles during oogenesis [74]. The absence of CCs during in vitro maturation alters the gene expression profile of MII oocyte Despite the fact that we did not observe significant mor- phological differences between oocyte matured with or without the surrounding cumulus cells including the polar body extrusion, previous study in bovine [38] has shown that oocytes matured without the surrounding cumulus cells resulted in significantly reduced blasto- cysts rates compared to those matured in the presence of the surrounding cumulus cells. Therefore, we hypothesized that the absence of cumulus cells during maturation can affect the nuclear and molecular maturation of the resulting oocytes. Maternal gene expression is an important biological process in oocyte maturation. If the oocyte is to complete normal