Morten Krog Larsen et al. (2007) International Worm Meeting "A new Calponin Homology domain protein required for efficient engulfment of apoptotic germline cells."

Morten Krog Larsen, Jyothsna Devi Chitturi, Simon Tuck

[International Worm Meeting, 2007]

The engulfment and removal of apoptotic cells is important both for development in metazoans and for maintaining tissue homeostasis in adult animals. The process has been studied extensively in C. elegans and pioneering work has revealed much of the underlying genetic program[1, 2]. Dying cells activate two parallel pathways in engulfing cells involving, in one case, ced-1, ced-6 and ced-7, and in the other, ced-2, ced-5 and ced-12[2]. These two pathways have been shown to converge on ced-10, which encodes the worm Rac1 homologue[3, 4]. ced-10 is required for the cytoskeletal changes necessary for efficient engulfment; in ced-10 mutants the actin halos that are normally generated within the engulfing cell fail to form[3]. Here we describe a new calponin homology domain protein that promotes engulfment of apoptotic germline cells. The protein binds directly to F-actin in vitro, suggesting that it affects engulfment by altering actin dynamics. Furthermore, the protein is found to localise around the periphery of germline apoptotic cells with highly condensed chromatin. Reduction of gene activity by RNAi causes defects in engulfment of germline cells. To investigate the gene in more detail we isolated two deletion alleles, sv63 and sv64, both likely to be strong hypomorphic or null alleles. The homozygous mutants display a fully penetrant sterile phenotype. Phalloidin staining of the maternally rescued animals indicates gross changes in actin distribution, particularly within the germline. When depleted of maternal gene activity, the mutant embryos display ventral enclosure defects similar to those seen in embryos completely lacking ced-10 activity[5]. In support of this finding, the protein is highly expressed in the leading migrating cells during ventral enclosure. Our experiments thus identify a new modulator of the actin cytoskeleton that affects both the engulfment of apoptotic cells in the germline as well as embryonic enclosure. References: 1.Ellis, R.E., J.Y. Yuan, and H.R. Horvitz, Annu Rev Cell Biol, 1991. 7: p. 663-98. 2.Lettre, G. and M.O. Hengartner, Nat Rev Mol Cell Biol, 2006. 7(2): p. 97-108. 3.Kinchen, J.M., et al., Nature, 2005. 434(7029): p. 93-9. 4.Reddien, P.W. and H.R. Horvitz, Nat Cell Biol, 2000. 2(3): p. 131-6. 5.Lundquist, E.A., et al., Development, 2001. 128(22): p. 4475-88.

Wu, M. et al. (2017) International Worm Meeting "Investigating the role and mechanism of UBR-1, the C. elegans homolog of the Johanson-Blizzard Syndrome causative E3 ligase."

Zhen, M., Hung, W., Wu, M., Susoy, V., Meng, J., Chitturi, J., Wang, Y.

[International Worm Meeting, 2017]

Johanson-Blizzard syndrome (JBS) is a recessive systemic disorder, characterized by a combination of congenital abnormalities including defects in the nervous system and pancreas. Loss of function mutations in an E3 ligase UBR1 are responsible for the disorder, but the underlying mechanisms of how the loss of UBR1 activity gives rise to the pleotropic symptoms of JBS remains elusive. Previously, our lab isolated several loss-of-function alleles of the C. elegans UBR-1, and found it to exhibit an altered bending pattern during reversal locomotion (Chitturi et al., manuscript in preparation). Here I present results that investigate the circuit defects that underlie this defect. Using CRISPR-Cas9-mediated genomic editing, I generated an allele of ubr-1 where the RING domain, critical for the E3 ligase activities, is removed. I found that the motor defects of this and other alleles of ubr-1 mutants are likely caused by motor state transitions. I am currently identifying the key cells through which UBR-1 regulates motor state transitions. Through investigating the C. elegans UBR-1 model, I aim to uncover the molecular pathways through which UBR-1 regulates neuronal and cellular functions.