Jiravat Visanuvimol et al. (2005) International Worm Meeting "A role for strabismus/van gogh in axon outgrowth."

Jiravat Visanuvimol, Antonio Colavita

[International Worm Meeting, 2005]

We use the VC motorneurons to investigate the molecular mechanisms regulating axon outgrowth and branching. VC neurons display a simple bipolar morphology with axons projecting along the ventral nerve cord and branching at the vulva. We are undertaking a genetic screen to identify VC axon outgrowth mutants using a cat-1::gfp reporter to label VC4 and VC5 neurons. So far, two classes of mutants that alter the normal bipolar morphology of VC neurons have been identified: mutants displaying a tripolar morphology and those displaying a single neurite morphology. We mapped one complementation group (2 alleles) that displayed a highly penetrant tripolar VC phenotype to a small interval on LGX near B0410.2, a homolog of the cell polarity gene Strabismus/Van Gogh (referred to as Stbm). We confirmed Stbm as our gene by rescuing with a genomic PCR fragment containing a single open reading frame and identifying sequence alterations in our mutants. Because Stbm acts in a Wnt signalling pathway to regulate planar cell polarity (PCP) and gastrulation movements in flies and vertebrates we are examining VC axon morphology in Wnt and PCP mutants to determine if C. elegans Stbm acts in a similar pathway to regulate VC neurite outgrowth or polarity. A preliminary characterization of tm306, a mutation in the PCP gene Flamingo (F15B9.7) (a gift from S. Mitani), however did not reveal defects in VC axon guidance or morphology. We will present our genetic and molecular characterization of Stbm and other mutants arising from the screen.

Jiravat Visanuvimol et al. (2007) International Worm Meeting "Planar Cell Polarity (PCP) signaling is involved in multiple aspects of C. elegans development."

Anna Su, Ian Chin-Sang, Leticia Sanchez Alvarez, Antonio Colavita, Jiravat Visanuvimol, Jeffrey Boudreau

[International Worm Meeting, 2007]

The Planar Cell Polarity (PCP) pathway is a highly conserved signaling pathway involved in organizing cells within tissues to create polarized structures or promote directed cell movements. For example, in mammals PCP signaling is involved in convergent extension and neural tube closure, inner ear development and hair orientation. In a genetic screen for neuronal polarity defects affecting the bipolar VC4 and VC5 egg-laying neurons, we identified missense mutations in the worm homologs of the core PCP genes van gogh/strabismus (vang-1(B0410.2)) and prickle (prkl-1(ZK381.5)). In addition to VC4/5 neuronal polarity defects we also observe cell migration defects, embryonic lethality and notched head phenotypes. While our primary focus is on understanding the novel role for PCP signaling in generating neuronal polarity in C. elegans we have begun to characterize the role of these PCP genes on other aspects of development. We will present localization data from GFP translational fusions and 4D analysis of the embryonic defects. We are also generating antibodies to VANG-1 and PRKL-1. Understanding how PCP signaling functions in different developmental contexts should provide insights into both the general and specific mechanisms employed to polarize cells.

Leticia Sanchez Alvarez et al. (2007) International Worm Meeting "A Novel Role for Planar Cell Polarity Pathway Genes in the Establishment or Maintenance of Neuronal Polarity."

Leticia Sanchez Alvarez, Jiravat Visanuvimol, Antonio Colavita, Anna Su, Janice Imai

[International Worm Meeting, 2007]

Most neurons in C. elegans are initially polarized along either the anterior-posterior (A/P) or dorsal-ventral (D/V) body axes. The bipolar VC4 and VC5 neurons are unique in sending processes around the vulva along a new medial-lateral axis created by the developing vulva. To understand how neuronal polarity is established along this late developing axis we performed a genetic screen to identify VC4/5 neurons with defects in bipolar morphology. In a large-scale genetic screen we identified 15 mutants that displayed highly penetrant ‘tripolar VC4/5 morphologies. In other words, in addition to normal VC4/5 processes extending laterally around the vulva, we also observed a third process projecting along the A/P axis away from the vulva. We mapped these mutants to 4 complementation groups: 3 alleles of a van gogh/strabismus homologue (vang-1), 4 alleles of a prickle homologue (prkl-1), 1 allele of dishevelled homologue (dsh-1), and 7 alleles of pvd-1 (Prkl and Vang-like Defects), a new gene on LGV. van gogh, prickle, and dishevelled are core components of Frizzled/Planar Cell Polarity (Fz/PCP) signaling, a highly conserved pathway involved in organizing cells within tissues to create polarized structures or promote directed cell movements. Several groups have recently shown that Wnt/Fz signaling regulates neuronal polarity and axon guidance along the A/P axis. Exploring this possibility, preliminary data suggest that Fz signaling may also be involved in the ectopic A/P process outgrowth observed in PCP mutants. Cell-specific rescue experiments indicate that these PCP genes act cell autonomously to promote VC4/5 bipolar morphology. Functional translational fusions to fluorescent proteins indicate that some of these components are also asymmetrically localized in VC4/5 cells. Overexpression experiments show that this asymmetric localization is functionally important for normal polarization. For example, prkl-1 overexpression in VC4/5 cells result in unipolar neurons. Taken together, we hypothesize that VC4/5 polarity along the mediolateral axis may be established and/or maintained by antagonizing Wnt/Fz signaling along the A/P axis. To the best of our knowledge, this is the first report that the PCP pathway regulates the polarity of individual neurons.

Leticia Sanchez-Alvarez et al. (2009) International Worm Meeting "PCP signalling polarizes C elegans motorneurons along the medial-lateral axis during organogenesis."

Antonio Colavita, Jiravat Visanuvimol, Anna Su, Janice Imai, Andrea McEwan, Leticia Sanchez-Alvarez

[International Worm Meeting, 2009]

To understand how neurons polarize in vivo we studied the morphology of two bipolar motorneurons (VC4 and VC5), which polarize medial-laterally (ML) to innervate the egg-laying system of C elegans. To identify genes responsible for the bipolar ML morphology we performed genetic screens to isolate worms with defective VC4/5 polarity. So far we have isolated mutations in prickle-1 (prickle homolog-1 LGIV, 4 alleles), vang-1 (Van Gogh homolog-1 LGX, 3 alleles) and dsh-1 (dishevelled homolog-1 LGII, 1 allele) genes that result in ectopic misdirected axons. VC4 & 5 neurons in prkl-1, vang-1 and dsh-1 mutants extend a third axon in the AP axis rendering neurons with tripolar morphology. Here we report that evolutionary conserved Planar Cell Polarity (PCP) genes prkl-1, vang-1 and dsh-1 mediate the ML orientation of VC4 and VC5 by suppressing ectopic axon outgrowth along the anterior-posterior axis. We explore the biological mechanism underlying the novel role for prkl-1, vang-1 and dsh-1 in the polarity of VC4 and VC5 by performing cell rescue experiments, loss and gain-of-function studies, examining the localization of functional translational fusions and analyzing the expression of transcriptional reporters.