It is well established that mitochondrial genome is strictly maternally inherited in mammalian, despite the fact that paternal mitochondria enter into oocyte during fertilization. To date, although some mechanisms have been extrapolated to interpret the elimination of paternal mitochondria, the exact mechanism still is unclear. Recent studies suggest that autophagy process and the ubiquitin-mediated degradation pathway may be involved in elimination of paternal mitochondria. However, the dynamic profiles of autophagy and ubiquitination associated with paternal mitochondria degradation have not been determined in mouse model. Through immunostaining with specific antibody LC3 and Ubiquitin and confocal microscopy, we investigated the dynamic profiles of LC3 and Ubiquitin signals in mouse embryos during preimplantation development. In addition, embryos were stained with MitoTracker Red for tracking the degradation process of paternal mitochondria. Our results showed that paternal mitochondria gradually degraded during postfertilization development, and sporadic paternal mitochondria were found at least in 16 cell embryos. LC3 and Ubiquitin signals appeared in the midpiece of sperm at 3 h postfertilization, and they were strictly colocalizated with paternal mitochondria from zygote to 2 cell embryo. Nevertheless, the colocalization became loose at 4 cell embryos, and gradually disappeared beyond 4 cell embryos. Our results confirmed that autophagy process and the ubiquitin-mediated degradation pathway may take part in the postfertilization remove of paternal mitochondria.

β-catenin is a cytoplasmic protein that participates in the assembly of cell-cell adherens junctions by binding cadherins to the cytoskeleton. In addition, it is a key component of the Wnt signaling pathway. Activation of this pathway triggers the accumulation of β-catenin in the nucleus, where it activates the transcription of target genes. Abnarmal accumulation of β -catenin is characteristic of polyposis coli(APC) or Axin tumor suppressor proteins, which regulates β-catenin degradation, or activating mutations in β-catenin molecule itself. Here we show that overexpression of Sox4 down-regulates wild type β-catenin in HEK 293 cells. The inhibitory effect of Sox4 on wild type β-catenin is apparently mediated by the ubiquitin- proteasoem system and requires an active glycogen synthase kinase 3β(GSK3β). Mutations in the N-terminus of β -catenin(S33Y) which compromise its degradation by the proteasomes or inhibition of GSK3β activity rendered β-catenin resistant to down-regulation by Sox4. In light of recent evidence that Sox4 expression is activated in colon and other tumors with β-catenin dysregulation, our findings suggest that Sox4 is part of a feedback inhibitory pathway for Wnt signaling in normal cells. Moreover, the mutations in APC, Axin or β-catenin in cancer cells appear to render β-catenin resistant to the effects of Sox4 inhibition.

Ubiquitin is a small polypeptide (10kDa) and ubiquitination is one of the post-translational modifications (PTMs) by ubiquitin protein, resulting in degradation of the target proteins by 26S proteasome complex. Here, we found that E3 ubiquitin ligase SINAT5, an Arabidopsis homolog of the Drosophila SINA RING-finger protein, directly interacts with LHY (late elongated hypocotyls), a component of the circadian oscillator, and DET1 (De-etiolated 1), a negative regulator of light-regulated gene expression. In addition, we also found that SINAT5 has an E3 ubiquitination activity for LHY but not for DET1. Interestingly, LHY ubiquitination by SINAT5 was inhibited by DET1, suggesting that flowering time through regulation of LHY stability by SINAT5 may be controlled by DET1. We are now investigating whether DET1 indeed involves in the regulation of the proteolytic turnover of the LHY by SINAT5 in vivo.