C. elegans BLOC-1 functions in trafficking to lysosome-related gut granules

PLoS One. 2012;7(8):e43043. doi: 10.1371/journal.pone.0043043. Epub 2012 Aug 15.

Abstract

The human disease Hermansky-Pudlak syndrome results from defective biogenesis of lysosome-related organelles (LROs) and can be caused by mutations in subunits of the BLOC-1 complex. Here we show that C. elegans glo-2 and snpn-1, despite relatively low levels of amino acid identity, encode Pallidin and Snapin BLOC-1 subunit homologues, respectively. BLOC-1 subunit interactions involving Pallidin and Snapin were conserved for GLO-2 and SNPN-1. Mutations in glo-2 and snpn-1,or RNAi targeting 5 other BLOC-1 subunit homologues in a genetic background sensitized for glo-2 function, led to defects in the biogenesis of lysosome-related gut granules. These results indicate that the BLOC-1 complex is conserved in C. elegans. To address the function of C. elegans BLOC-1, we assessed the intracellular sorting of CDF-2::GFP, LMP-1, and PGP-2 to gut granules. We validated their utility by analyzing their mislocalization in intestinal cells lacking the function of AP-3, which participates in an evolutionarily conserved sorting pathway to LROs. BLOC-1(-) intestinal cells missorted gut granule cargo to the plasma membrane and conventional lysosomes and did not have obviously altered function or morphology of organelles composing the conventional lysosome protein sorting pathway. Double mutant analysis and comparison of AP-3(-) and BLOC-1(-) phenotypes revealed that BLOC-1 has some functions independent of the AP-3 adaptor complex in trafficking to gut granules. We discuss similarities and differences of BLOC-1 activity in the biogenesis of gut granules as compared to mammalian melanosomes, where BLOC-1 has been most extensively studied for its role in sorting to LROs. Our work opens up the opportunity to address the function of this poorly understood complex in cell and organismal physiology using the genetic approaches available in C. elegans.

MeSH terms

  • Animals
  • Caenorhabditis elegans / genetics
  • Caenorhabditis elegans / metabolism*
  • Caenorhabditis elegans Proteins / genetics
  • Caenorhabditis elegans Proteins / metabolism*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cytoplasmic Granules / metabolism*
  • Hermanski-Pudlak Syndrome / genetics
  • Hermanski-Pudlak Syndrome / metabolism
  • Humans
  • Lysosomes / metabolism*
  • Protein Binding
  • Two-Hybrid System Techniques

Substances

  • Caenorhabditis elegans Proteins
  • Carrier Proteins

Grants and funding

This work was supported by grants from the National Science Foundation (MCB-0716280 and MCB-1120835), the Howard Hughes Medical Institute, the James F. and Marion L. Miller Foundation and the John S. Rogers Summer Research Program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.