Background

Macroautophagy (hereafter autophagy) is an essential, evolutionarily conserved cellular degradation and recycling process in all eukaryotes [1]. The role of autophagy is to maintain cellular homeostasis by degrading intracellular components. Autophagy is a process involving induction, cargo recognition and packaging, vesicle formation, and breakdown. A series of autophagy-related (Atg) genes are required for the initiation, nucleation, expansion, and completion of bodies known as autophagosomes, which eventually fuse with lysosomes [2]. Autophagy is essential to many physiological and developmental processes, and defects in autophagy are often associated with diseases and tumor progression [3, 4].

Autophagy is regulated by several ATG proteins, which are evolutionary conserved from yeast to mammals, ATG proteins are classified into six functional complexes including ATG1-kinase complex, phosphatidylinositol-3-kinase complex, ATG2-ATG18 complex, ATG9 membrane protein, ATG8 conjugation system and ATG12 conjugation system [5]. ATG4 is the only cysteine protease specific to ATG8, and essential for the conjugation and deconjugation of ATG8. Although ATG4 and ATG8 are evolutionarily conserved, higher eukaryotes have multiple homologs for both proteins. In contrast to the Atg4 and Atg8 in yeast, there are four ATG4 and six ATG8 homologs in mammals, the protease activity of the ATG4 homologs is markedly different, but ATG4B exhibits much higher activity than the other homologs [6, 7]. ATG4 homologs are important for autophagosome formation, autophagy is inhibited by suppressing ATG4 expression [8]. In B. mori, 15 Atgs have been identified in the genome [9, 16]. In the last decades, advances in transcriptome sequencing have led to the identification of a large number of lncRNAs in various eukaryotic organisms using new technologies and bioinformatics methods [17,18,19,20,21,22], but there are still few studies into their functions. Recently, lncRNAs have attracted attention because of their critical roles in organismal growth, development, senescence, and death. There is evidence that lncRNAs participate in a range of biological processes, such as X-chromosome silencing [Full size image

Based on these results, and those of previous studies [Full size image