Development of the Caenorhabditis elegans foregut (pharynx) is regulated by a network of proteins that includes the Retinoblastoma protein (pRb) ortholog LIN-35; the ubiquitin pathway components UBC-18 and ARI-1; and PHA-1, a cytoplasmic protein. Loss of pha-1 activity impairs pharyngeal development and body morphogenesis, leading to embryonic arrest. We have used a genetic suppressor approach to dissect this complex pathway. The lethality of pha-1 mutants is suppressed by loss-of-function mutations in sup-35/ztf-21 and sup-37/ztf-12, which encode Zn-finger proteins, and by mutations in sup-36. Here we show that sup-36 encodes a divergent Skp1 family member that binds to several F-box proteins and the microtubule-associated protein PLT-1/t. Like SUP-35, SUP-36 levels were negatively regulated by UBC-18-ARI-1. We also found that SUP-35 and SUP-37 physically associated and that SUP-35 could bind microtubules. Thus, SUP-35, SUP-36, and SUP-37 may function within a pathway or complex that includes cytoskeletal components. Additionally, SUP-36 may regulate the subcellular localization of SUP-35 during embryogenesis. We carried out a genome-wide RNAi screen to identify additional regulators of this network and identified 39 genes, most of which are associated with transcriptional regulation. Twenty-three of these genes acted via the LIN-35 pathway. In addition, several S-phase kinaseassociated protein (Skp)1-Cullin-F-Box (SCF) components were identified, further implicating SCF complexes as part of the greater network controlling pharyngeal development.

To adapt to stress, cells must undergo major changes in their gene expression profiles. We have previously described a largely uncharacterized stress response pathway in Caenorhabditis elegans that acts through an evolutionarily conserved motif, termed ESRE, for ethanol and stress response element. We characterize here the requirements for ESRE gene expression and show that the ESRE network is regulated by a conserved SWI/SNF family nucleosome remodeling complex termed PBAF. Depletion of PBAF subunits SWSN-7/BAF200 and PBRM-1/BAF180 results in decreased expression of ESRE genes and increased sensitivity to thermal stress. When overexpressed, SWSN-7/BAF200 and PBRM-1/BAF180 led to increased ESRE transcription, enhanced thermotolerance, and induction of a nuclear ESRE-binding activity. Our data support a model in which PBAF is recruited by an ESRE-binding protein to genomic ESRE sites. We also show that the closely related SWI/SNF complex, BAF, which regulates stress induction through DAF-16/FOXO, does not contribute to ESRE gene expression or bind directly to ESRE sites. To our knowledge, this is the first report demonstrating direct and specific regulation of a stress response network by the PBAF nucleosome-remodeling complex in vivo in metazoa. In addition, we show that PBAF cooperates with the histone demethylase, JMJC-1/NO66, to promote expression of ESRE genes following stress.

No abstract