Hannah Nicholas et al. (2007) International Worm Meeting "The C. elegans CTBP-1 repressor protein contains a DNA-binding THAP domain."

Joel Mackay, Chu Kong Liew, Tina Wu, Merlin Crossley, Hannah Nicholas

[International Worm Meeting, 2007]

Transcriptional co-repressors of the C-terminal binding protein (CtBP) family interact with other proteins that contain amino acid motifs of the form PXDLS. These motifs occur in many transcription factors, and serve to recruit CtBP and its associated repression complex to DNA-regulatory elements. In mammals there are two CtBP genes, with overlapping functions. Disruption of both genes leads to early lethality. In C. elegans there is a single CtBP-related gene. We have shown that the worm CtBP (CTBP-1) binds PXDLS-containing transcription factors and can repress transcription, indicating that the nematode protein is functionally orthologous to other CtBPs. C. elegans therefore provides a tractable model system for investigating CtBP function. Interestingly, the CTBP-1 protein contains an additional domain not found in other characterised members of the CtBP family, which homology searches have identified as a THAP domain. We have shown that this domain can bind to double-stranded DNA and, through site-selection experiments, we have identified a consensus binding sequence. Using nuclear magnetic resonance spectroscopy we have determined the structure of the THAP domain of CTBP-1 and shown that it contains a positively charged face that may correspond to the DNA-contact surface. The C. elegans CtBP protein is the first CtBP protein with intrinsic DNA-binding capacity and may serve as a DNA-binding transcriptional repressor in vivo. In order to examine the in vivo roles of CTBP-1, we have obtained a ctbp-1 deletion allele from the C. elegans knockout consortium. Worms carrying this allele display a mild uncoordinated phenotype. Progress towards a molecular understanding of this phenotype will be presented.

Hannah Nicholas et al. (2007) First Australian C. elegans Meeting "Caenorhabditis elegans as a model in which to investigate the functions of a transcriptional co-repressor"

Joel Mackay, Hannah Nicholas, Tina Wu, Merlin Crossley, Chu Kong Liew

[First Australian C. elegans Meeting, 2007]

Transcriptional co-repressors of the C-terminal binding protein (CtBP) family interact with other proteins that contain amino acid motifs of the form PXDLS. These motifs occur in many transcription factors, and serve to recruit CtBP and its associated repression complex to DNA-regulatory elements. In mammals there are two CtBP genes, with overlapping functions. Disruption of both genes leads to early lethality. We have identified a single CtBP-related gene in C. elegans. This worm CtBP (CTBP-1) binds PXDLS-containing transcription factors and can repress transcription, indicating that the nematode protein is functionally orthologous to other CtBPs. C. elegans therefore provides a tractable model system for investigating CtBP function. We have begun investigating CTBP-1. This protein contains an additional domain not found in other characterised members of the CtBP family, which homology searches have identified as a THAP domain. We have shown that the domain can bind to double-stranded DNA. We have also determined the structure of this domain and shown that it contains a positively charged face that may correspond to the DNA-contact surface. The C. elegans CtBP protein is the first CtBP protein with an intrinsic DNA-binding function and may serve as a DNA-binding transcriptional repressor in vivo.. In order to examine the in vivo roles of CTBP-1, we have obtained a ctbp-1 deletion allele from the C. elegans knockout consortium. Worms carrying this allele display a mild uncoordinated phenotype. Progress towards a molecular and cellular explanation of this phenotype will be presented.

Lord , A. et al. (2019) International Worm Meeting "TXBP-3 regulates C. elegans cell adhesion and spermathecal contractility."

Cram, Erin, Zaidel-Bar, Ronen, Lord , A.

[International Worm Meeting, 2019]

Proteins containing PDZ domains function primarily as molecular scaffolds that recruit target proteins in order to promote cell signaling, cell adhesion, and protein scaffolding. TAX1BP3 is a highly conserved protein with a single atypical PDZ domain. Little is known about the C. elegans homolog, TXBP-3, although it has been shown to interact with the FERM family protein NFM-1/merlin. TXBP-3 is expressed in the pharynx, vulval precursor cells, spermatheca, and rectal epithelial cells of C. elegans. The current study investigates the role of TXBP-3 in the spermatheca as a model for understanding the coordination of contractility in a tube and to elucidate the function of TXBP-3 in the regulation of anchoring proteins, such as actin, to the cytoskeleton. TXBP-3 relocalizes from the apical to the basal surface of the spermatheca upon ovulation of oocytes into the spermatheca. Overexpression of TXBP-3 results in more rapid embryo transit times during the first three ovulations, which may be caused by a downstream effect on RHO-1, a major contributor to spermathecal contractility. Previous research indicates that TAX1BP3 is necessary for the redistribution of Rhotekin, a Rho GTPase effector that is conserved in C. elegans, which suggests a potential role of TXBP-3 in the regulation of this important pathway. We also demonstrate that CRISPR deletion of a coding region of TXBP-3 results in slower transit times and causes a "lace nose" phenotype, where the worm appears to have large vacuoles along both sides of the nose, possibly due to mis-localization of anchoring proteins. We aim to characterize the TXBP-3 gene and identify its interactors in order to better understand how it affects cytoskeletal organization and cell signaling.

Verena Goebel et al. (2001) International C. elegans Meeting "The cytoskeletal linker ERM is required for the integrity of epithelial luminal surfaces of internal organs in C. elegans"

John Fleming, Olaf Bossinger, Verena Goebel, Peter Barrett, David H Hall

[International C. elegans Meeting, 2001]

We are interested in the role of submembraneous cytoskeletal linker proteins of the protein 4.1 family in growth regulation and morphogenesis and have previously reported the identification of two C. elegans members of the ezrin-radixin-moesin-merlin family, erm and nfm (previously called nf2 ). The highly conserved C. elegans homolog of ezrin-radixin-moesin, erm , is predominantly expressed in apical epithelial membranes of the digestive tract, excretory system and somatic gonad. Its loss during embryonic development induces early larval lethality with extensive morphogenesis defects in the digestive and excretory organs. Death occurs at L1 subsequent to the appearance of cysts that were found to be diverticula of the lumina of the intestine and excretory system. The intestinal cysts can run the full length of the gut, and the excretory cysts can fill the head, pressing the pharynx or anterior intestine against the bodywall. Confocal analysis of the intestine using antibodies against proteins localized to adherens junctions, to the apical and baso-lateral membranes and to actin, indicate that the polarity of the epithelium is preserved, but that cell shapes can be grossly distorted by the cysts or by defects of the epithelial tube formation. Ultrastructural analysis of L1s by TEM demonstrates loss of microvilli in the intestinal lumen in the cystic region, but adherens junctions are still intact. Judging by TEM, posterior intestinal cells appear to be less well organized into an epithelial tube. By TEM, the excretory canals are found to be missing, shortened and/or to contain large cysts, and connections between the canal, duct and pore cells are often missing. ERM is also expressed within the somatic gonad in the spermatheca, the uterus and the vulval opening. Loss of erm during larval development induces severe defects in gonad morphogenesis. The uterine wall (and perhaps the spermatheca) may fail to form a proper epithelium or may fail during use, so that developing embryos and adult sperm leak into the body cavity. Thus all three organ systems show defects in luminal epithelia. We propose that erm is required for the integrity of luminal surfaces of internal organs in C. elegans .