The Comparative Research Of Paternal Mitochondrial DNA Elimination In Yellow Catfish And Hybrid Yellow Catfish

Mitochondrial genome is inherited uniparentally from the maternal parent in the great majority of eukaryotes.The delayed elimination of paternal mtDNA is always shown in the interspecies hybrid,and even the phenomenon of paternal mtDNA leakage.In mammals,mtDNA heteroplasmy usually leads to abnormal or diseased phenotypes.And the high embryonic lethality is caused by the delayed elimination of paternal mtDNA in C.elegans.Therefore,mitochondria homoplasmy is essential for normal development.In recent years,hybrid yellow catfish from mating female yellow catfish(Pelteobagrus fulvidraco)with male darkbarbel catfish(Pelteobaggrus vachelli)has been widely cultured in China.However,a high rate of abnormal and defective embryos was observed in hybrid yellow catfish.Therefore we propose that the delayed elimination of paternal mitochondrial DNA may be one of the main factors that cause the high malformation in hybrid yellow catfish.In this study,we systematically investigate the elimination process of paternal mitochondria DNA(mtDNA)in yellow catfish and hybrid yellow catfish.First,the mature sperms are separated by centrifugation on discontinuous Percoll gradient,and we calculate the mtDNA copies of semen and mature sperm with the absolute quantitative real-time PCR assay.The results show that the mtDNA contents significantly decrease in the isolated mature sperm compared with the semen between yellow catfish and hybrid yellow catfish.Then we search the different sites of the parents between yellow catfish and hybrid yellow catfish,and detect that paternal mtDNA is immediately eliminated after fertilization in yellow catfish by direct sequencing.Moreover,the sequencing results show that paternal mtDNA is detected at as later as gastrula stage in hybrid yellow catfish,and we have further proved this result by enzyme digestion,indicating a delay of elimination for paternal mtDNA during embryogenesis in hybrid yellow catfish.The reasons of delayed paternal mitochondrial elimination are not clear yet,but there are some recognized mechanisms,including autophagy,ubiquitin-proteasome system and specific nuclease-dependent system.We treat the hybrid yellow catfish embryos with rapamycin and observe the percentage of embryo malformation.The results show that rapamycin can't reduce the percentage of embryo malformation.We guess that there are many pathways to induce autophagy,and rapamycin is mTOR inhibitor,which promotes autophagsome formation only by inhibiting MTORC1 activity.And it's also possible that paternal mtDNA elimination of hybrid yellow catfish depends primarily on ubiquitin-proteasomal system,specific nuclease-dependent system or the synergistic effect of autophagy and the ubiquitin-proteasomal system.In conclusion,our findings confirmed the delayed elimination of paternal mitochondrion in hybrid yellow catfish,which may provide a possible research clue of abnormal embryonic development of hybrid progeny.