190 SPINDLIN 1 IS REQUIRED FOR METAPHASE II ARREST IN PORCINE OOCYTES

Spindlin 1 (Spin1), is a histone methylation effecter protein. It can specifically recognise and bind to trimethylated histone 3 lysine 4 (H3K4). Spin1 localizes to the active rDNA repeats and facilitates the expressions of rRNA genes. For exploring the function of Spin1 in porcine oocyte and embryo development, siRNA of Spin1 (siSpin1) was used in the present study. Messenger RNA level of Spin1 was more highly expressed in the ovary than other tissues. During oocyte maturation, Spin1 was highly expressed from germinal vesicle to metaphase II stage in oocyes but sharply decreased after zygotic genome activation. The SPIN1 protein was localised to the cytoplasm and showed a similar expression pattern with mRNA through all stages of early embryonic development. Spin1 was successfully knocked down by siRNA injection. The siRNA of green fluorescent protein (siGFP) was used as positive control, and distilled water (DW) was used as a negative control. All were injected at metaphase II stage. Oocyte maturation was not altered by siSpin1 microinjection, but the rate of embryo development was significantly decreased from 4-cell stage when compared with the control group. The Spin1 had an effect on the blastocyst formation, which may have been altered by polymerase I-mediated rRNA gene transcription via regulation of H3K4 methylation. On the other hand, pronuclear formation was reduced by Spin1 siRNA. All data were analysed with a one-way analysis of variance, and differences between treatment groups were assessed by l.s.d. test, using SPSS software. In conclusion, Spin1 may be involved in metaphase arrest in oocyte and zygotic genome activation during early embryo development in pigs.