Overexpression of Atg4.1 Promote Parental Macronucleus Programmed Degradation in Tetrahymena thermophila
Zheng Wenping1, Bo Tao1, Liu Ya1, Xu Jing1,2, Wang Wei1*
Nuclear autophagy plays an important role in the evolution of eukaryotes. However, the molecular mechanism of the autophagy is not fully understood in different organisms. The programmed nuclear death (PND) of the parental macronucleus during the sexual reproduction of Tetrahymena thermophila is a novel selective autophagy. In this study, autophagy-related gene TtATG4.1 (TTHERM_00526270) encoding 677 amino acids was identified from T. thermophila. TtATG4.1 was not expressed during vegetative growth and starvation, but specifically expressed during conjugation stage. The expression level of TtATG4.1 was the highest during anlagen period with parental macronucleus degradation. MTT1-HA-Atg4.1 mutants were created by homologous recombination. Immunostaining showed that HA-Atg4.1 localized in the cytoplasm during early stage of sexual reproduction, and localized in the parental macronucleus in later conjugation stage. When Atg4.1 was overexpressed, the volume of parental macronucleus failed to condense normally and became larger. The acidification of parent macronuclei was not affected in overexpressing TtATG4.1 paired cells. However, the degradation rate of parental macronucleus was faster in overexpressing TtATG4.1 cells at 12 h for sexual reproduction stage. The results indicated that the autophagy-related protein Atg4.1 was involved in the regulation of parental macronucleus programmed degradation during the stage of sexual reproduction of T. thermophila.
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