Research Projects

I. Apoptosis

Our lab has a long standing interest in cellular suicide, also known as programmmed cell death (PCD, or apoptosis). This includes understanding how the p53-like gene cep-1 integrates stresses, such as damage to the genmoe, to determine whether a cell lives or dies.  We have identified several novel regulators of cep-1-dependent apoptosis through genetics and functional genomics methods, such as RNA interference (RNAi) screens.

i) Insulin/PI3K signaling

We recently discovered that the Akt/PKB gene akt-1 regualtes cep-1-dependent germline apoptosis by a novel mechanism (Quevedo et al., 2007).   One mechanism by which mammalian Akt/PKB regulates apoptosis is through the phosphorylation and activation of the p53-directed E3 ubiquitin ligase Mdm2.   However, we have not been able to identify an Mdm2 orthologue in the C. elegans genome or an E3 ligase that functions between akt-1 and cep-1. Therefore, to determine how akt-1 regulates cep-1 we are using a combination of genetics and proteomics approaches to uncover AKT-1 substrates that control CEP-1 activity.

We have expanded our analysis of akt-1 to the insulin/PI3K signaling pathway where we have uncovered several unexpected bifurcations in this "linear" pathway that intersect the apoptosis pathway at different levels. We are currently investigating the genetic and biochemical mechanisms by which the insulin signaling communicates with the apoptosis pathway to promote apoptosis independently of cep-1.

ii) Ubiquitination

Based on an RNAi screen that uncovered genes in the ubliquitin proteolysis cascade we carried out a comprehensive screen of all predicted E3 ubiquitin ligases in the C. elegans genome for roles in DNA damage-induced germ cell apoptosis. We discovered that the transcriptional activity and levels of endogenous CEP-1 protein are negatively regulated by neddylation (a ubiquitin like protein modification) that converges on the Skp1/cullin/F-box E3 ligase SCF^FSN-1 (Gao et al., 2008).   This ligase was originally shown by our collaborator Dr. Mei Zhen to regulate neuromuscular synapse formation in C. elegans.  We are collaborating with Dr. Zhen to investigate how genetic modifiers of fsn-1 regulate cep-1-dependent germline apoptosis.

From the ubiquitin ligase screen we also identified the HECT class of E3 ubiquitin ligases eel-1 as a positive regulator of DNA damage-induced germline apoptosis (Ross et al., 2011).   EEL-1 is homologous to the human Huwe1 protein (also known as ARF-BP1 or Mule) and has been shown to target p53 and Mcl-1 for degradation.  We are investigating how eel-1/Huew1 regulates germline apoptosis independent of cep-1/p53.

iii) Cell-nonautonomy

The activation of apoptosis by DNA damage has been thought to occur in a cell autonomous manner. We identified a gene called kri-1 that is required to activate germline apoptosis in response to genotoxic stress by a mechanism that is independent (or downstream) of cep-1. Interestingly, we showed that kri-1 is required outside the germline (in somatic tissue) to promote germ cell apoptosis, suggesting a cell-nonautonomous contribution to apoptosis that is similar to "assisted suicide" (Ito et al., 2010). The kri-1 gene is an orthologue of CCM1/Krit1, which is frequently mutated in the human neurovascular disease cerebral cavernous malformations (CCM). We are currently developing a worm model of CCM disease and screening for genes in the operate in the kri-1 pathway to promote germline apoptosis. 

II. Modeling cerebral cavernous malformations

Our discovery of an apoptotic function for kri-1 stimulated our interests in CCM disease.  The three familial CCM genes (CCM1/Krit1, CCM2/malcavernin, CCM3/PDCD10) all function in cross-tissue signaling in vertebrates and are required for proper cell adhesion in the neural vasculature. We extended our analysis of the CCM regulatory network to include the worm ccm-3 gene, which we found to be required for development of the excretory cell, a vascular structure in the worm that is believed to functions as a primitive kidney. Our long term goal is to define the CCM regulatory network and proteome in collaboration with our local colleagues, Dr. Anne-Claude Gingras,Dr. Frank Sicheri andDr. Ian Scott.