Full-length cDNA cloning of M and F-type COⅡ genes and expression in different age freshwater mussel Hyriopsis cumingii

The mitochondrial genetic patterns of bivalve mollusc are different from the traditional maternal inheritance. The mitochondria of bivalve molluscs have two kinds of mtDNA of M type and F type, which are called doubly uniparental inheritance (DUI). In order to explore the mechanism of DUI, the full-length cDNA of M and F-type COⅡ genes in Hyriopsis cumingii was obtained by RACE. qRT-PCR was used to detect the expression of M and F-type COⅡ genes in different tissues and stages. The results are as follows: 1.The full-length cDNA sequences of M-type COⅡ gene and F-type COⅡ gene were 1244 bp and 808 bp respectively, and the 3′ end of M-type COⅡ gene had a prolonged sequence of 546 bp. The transmembrane structure prediction showed that there were four transmembrane structures in the C-terminus extension region of the M-type COⅡ gene, suggesting that this extension sequence has certain function. 2. M-type COⅡ gene and F-type COⅡ gene were all expressed in the early juvenile (embryonic to 5-month-old) of H.cumingii, and the expression level of F-type COⅡ gene was significantly higher than that of M-type COⅡ gene. 3. In the tissues of six-month-old mussels, the expression of M-type COⅡ gene was the highest in gonads, and the expression of F-type COⅡ gene was still at a high level in the same tissues. 4. In the one-year-old female tissues, M and F-type COⅡ genes can be detected in all tissues. In male tissues, the F-type COⅡ gene was detected in each tissues, but M-type COⅡ gene was only expressed in gonads. 5. In the two-year-old female tissues, F and M type both expressed in each tissue, but the expression of M-type COⅡ gene is very low. In the two-year-old male tissues, the F-type COII gene was detectable in addition to the gonad, and the M-type COⅡ gene was detected only in the gonad. In the two-year-old male tissues, the F-type COⅡ gene was detectable except for the gonad, and the M-type COⅡ gene was detected only in the gonad. These results suggested that M-type mtDNA is selectively degraded or aggregated in tissues during male and female development of H. cumingii.