A systematic screen of Cdc42 targets was carried out in human bronchial epithelial cells. Two kinases, PAK4 and Par6B/aPKC, were identified and are required for maturation of primordial junctions into apical junctions. PAK4 recruitment to primordial junctions is Cdc42-dependent, but maintenance at junctions during maturation is Par6B-dependent.

SUMMARY Sensory neurons are an animal’s gateway to the world, and their receptive endings, the sites of sensory signal transduction, are often associated with glia. While glia are known to promote sensory-neuron functions, the molecular bases of these interactions are poorly explored. Here we describe a post-developmental glial role for the PROS-1/Prospero/PROX1 homeodomain protein in sensory-neuron function in C. elegans. Using glia expression profiling, we demonstrate that, unlike previously characterized cell fate roles, PROS-1 functions post-embryonically to control sense-organ glia-specific secretome expression. PROS-1 functions cell autonomously to regulate glial secretion and membrane structure, and non-cell autonomously to control the shape and function of the receptive endings of sensory neurons. Known glial genes controlling sensory-neuron function are PROS-1 targets, and we identify additional PROS-1-dependent genes required for neuron attributes. Drosophila Prospero and vertebrate PROX1 are expressed in post-mitotic sense-organ glia and in astrocytes, suggesting conserved roles for this class of transcription factors.

Rho GTPases regulate multiple signaling pathways to control a number of cellular processes during epithelial morphogenesis. To investigate the downstream pathways through which Rho regulates epithelial apical junction formation, we screened a small interfering RNA (siRNA) library targeting 28 known Rho target proteins in 16HBE human bronchial epithelial cells. This led to the identification of the serine-threonine kinase PRK2 (protein kinase C-related kinase 2, also called PKN2). Depletion of PRK2 does not block the initial formation of primordial junctions at nascent cell-cell contacts but does prevent their maturation into apical junctions. PRK2 is recruited to primordial junctions, and this localization depends on its C2-like domain. Rho binding is essential for PRK2 function and also facilitates PRK2 recruitment to junctions. Kinase-dead PRK2 acts as a dominant-negative mutant and prevents apical junction formation. We conclude that PRK2 is recruited to nascent cell-cell contacts through its C2-like and Rho-binding domains and promotes junctional maturation through a kinase-dependent pathway.

Sensory organ glia surround neuronal receptive endings (NREs), forming a specialized compartment important for neuronal activity, and reminiscent of glia-ensheathed synapses in the central nervous system. We previously showed that DAF-6, a Patched-related protein, is required in glia of the C. elegans amphid sensory organ to restrict sensory compartment size. LIT-1, a Nemo-like kinase, and SNX-1, a retromer component, antagonize DAF-6 and promote compartment expansion. To further explore the machinery underlying compartment size control, we sought genes whose inactivation restores normal compartment size to daf-6 mutants. We found that mutations in igdb-2, encoding a single-pass transmembrane protein containing Ig-like and fibronectin type III domains, suppress daf-6 mutant defects. IGDB-2 acts in glia, where it localizes to glial membranes surrounding NREs, and, together with LIT-1 and SNX-1, regulates compartment morphogenesis. Immunoprecipitation followed by mass spectrometry demonstrates that IGDB-2 binds to LGC-34, a predicted ligand-gated ion channel, and lgc-34 mutations inhibit igdb-2 suppression of daf-6. Our findings reveal a novel membrane protein complex and suggest possible mechanisms for how sensory compartment size is controlled.

SUMMARY Animals encounter microorganisms in their habitats, adapting physiology and behavior accordingly. The nematode Caenorhabditis elegans is found in microbe-rich environments; however, its responses to fungi are not extensively studied. Here, we describe interactions of C. elegans and Penicillium brevicompactum , an ecologically relevant mold. Transcriptome studies reveal that co-culture upregulates stress response genes, including xenobiotic-metabolizing enzymes (XMEs), in C. elegans intestine and AMsh glial cells. The nuclear hormone receptors (NHRs) NHR-45 and NHR-156 are induction regulators, and mutants that cannot induce XMEs in the intestine when exposed to P. brevicompactum experience mitochondrial stress and exhibit developmental defects. Different C. elegans wild isolates harbor sequence polymorphisms in nhr-156 , resulting in phenotypic diversity in AMsh glia responses to microbe exposure. We propose that P. brevicompactum mitochondria-targeting mycotoxins are deactivated by intestinal detoxification, allowing tolerance to moldy environments. Our studies support the idea that C. elegans NHRs may be regulated by environmental cues.