Abstract
The insulin/IGF-1 signalling (IIS) pathway plays an important role in the regulation of larval diapause, the long-lived growth arrest state called dauer arrest, in Caenorhabditis elegans. In this nematode, 40 insulin-like peptides (ILPs) have been identified as putative ligands of the IIS pathway; however, it remains unknown how ILPs modulate larval diapause. Here we show that the secretory polarity of INS-35 and INS-7, which suppress larval diapause, is changed in the intestinal epithelial cells at larval diapause. These ILPs are secreted from the intestine into the body cavity during larval stages. In contrast, they are secreted into the intestinal lumen and degraded during dauer arrest, only to be secreted into the body cavity again when the worms return to developmental growth. The process that determines the secretory polarity of INS-35 and INS-7, thus, has an important role in the modulation of larval diapause.
Highlights
WT # N.S. # #ins-35p ges-1p osm-6p myo-3p ins-35(ok3297)likely to be due to uptake into coelomocytes of secreted INS-35::VENUS
We found that knockdown of only ins-35 resulted in statistically significant promotion of dauer arrest (Supplementary Table 1)
From L1 to L4 stages, INS-35::VENUS fluorescence was observed in the intestine, chemosensory neurons and coelomocytes, which are scavenger cells that constitutively endocytose material secreted into the body cavity[17,18] (Fig. 1a)
Summary
INS-35 critically suppresses dauer arrest in the intestine. To investigate whether type-a ILPs modulate larval diapause, we first performed RNAi-mediated knockdown[12] of type-a insulin-like genes. 13) resulted in statistically significant promotion of dauer arrest (Supplementary Table 1). This promotion was shown by ins-35(ok3297) mutants in the presence of dauer-inducing pheromone[14] (Fig. 1). From L1 to L4 stages, INS-35::VENUS fluorescence was observed in the intestine, chemosensory neurons and coelomocytes, which are scavenger cells that constitutively endocytose material secreted into the body cavity (pseudocoelom)[17,18] (Fig. 1a). The fluorescence was observed in the intestine and coelomocytes (Fig. 1b). At the non-dauer (L2-L3) stages, VENUS fluorescence was observed in the intestine and chemosensory neurons. We could not detect fluorescence in coelomocytes at both non-dauer and dauer stages likely due to absence of a signal sequence in VENUS (Supplementary Fig. 2).
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