Molecular mechanisms controlling development and ageing in C. elegans
Co-workers: Sara Maxwell, Hayley Lees, Huajiang Xiong, Sophie Gilbert, Serena Ding, Karolina Chocian
Research in my group focuses on developmental genetics in the nematode Caenorhabditis elegans, Our overall aim is to understand how gene networks encode developmental and life span programmes, and in doing this we seek to integrate molecular mechanisms into a whole organism level of understanding. One major interest at present is the regulation of cell number and positioning during development. The transition from cell proliferation to differentiation is a key regulatory step in the development and subsequent maintenance of an organism's tissues and organs, and is of course at the heart of disease processes such as cancer. At present, molecular mechanisms controlling the balance between proliferation and differentiation of cells are poorly understood and we aim to use C. elegans as a powerful model organism in which to gain a molecular understanding of how this balance is achieved during normal development. Stem cells have the ability to both self-renew as well as give rise to differentiating daughters that can sometimes generate (or even re-generate) a particular tissue over the lifetime of an organism. Stem cells therefore need to constantly juggle the conflicting demands of proliferation and differentiation in order for a multicellular organism to develop and operate properly.
Our main focus at present involves trying to understand the molecular genetics of cell proliferation and differentiation in a particular stem cell lineage, the seam cell lineage, involved in the generation of male specific sense organs. Seam cells in C. elegans are neuroectodermal cells that provide a useful paradigm for the stem cell mode of division, as they divide throughout larval development to produce one daughter that retains the seam stem cell fate of further proliferation, and one daughter that differentiates, as a result of asymmetric division. They also undergo symmetrical self-renewing divisions at the beginning of each larval stage (and additionally in males) in order to expand the number of progenitors.
The great strength of using C. elegans as a model system for studying cell fate patterning, apart from its excellent genetic and genomic resources, is the fact that the developmental cell lineage is invariant and has been completely described. This means that lineage aberrations can be analysed at cellular resolution.
We have isolated and analysed various genes that act as key regulators of seam cell development. For example, the rnt-1 and bro-1 transcription factors are required for seam self proloferation. These genes are homologous to mammalian Runx and CBFβ factors, which are known to be de-regulated in various forms of cancer, particularly those, like leukaemias, that involve stem cell lineage aberrations. Thus, our work on these genes in C. elegans is likely to shed light on the function and regulation of these important cancer-associated genes. Other genes of current interest include Meis/Pbx transcription factors, Cdx class homeobox genes and other non-transcription factor genes. The overall aim is to delineate a framework for the molecular control of the development of a whole cell lineage.
A second more recent focus is the control of biological ageing. How is it that the extraordinarily complex process of ageing can be manipulated by mutations in just a single gene? An important aim is not simply to understand how the lifespan of an organism is regulated but to understand more about healthspan. Is it possible to manipulate genes such that age-associated disease and morbidity is alleviated? We have two main approaches to studying the genetics of ageing. The first is to try to understand the epigenetic architecture of ageing animals and to this end we have isolated and are analysing a number of chromatin modulators that lengththen lifespan and healthspan when inactivated. The second approach is to look at novel mutant combinations that have unexpected longevity effects - for example inactivating two deleterious genes and finding that double mutant animals have enhanced lifespan. Thus, existing genetic resources can be exploited in new ways to provide novel insights.
Finally we are interested in using the unique features of C. elegans as a useful invertebrate model organism in more applied areas of biological research. This involves collaboration with industries focussed on drug testing, acquisition of resistance and developmental and reproductive toxicity assessment.
Samantha Hughes, Henry Wilkinson, Sophie Gilbert, Marcia Kishida, Serena Ding and Alison Woollard. The C. elegans TPR containing protein, TRD-1, regulates cell fate choice in the developing germ line and epidermis. PLoS One 9, e114998, 2014
LaBonty et al. CACN-1/Cactin plays a role in Wnt signaling in C. elegans. PLoS One 9, e101945, 2014
Samantha Hughes, Charles Brabin, Peter J Appleford and Alison Woollard. CEH-20/Pbx and UNC-62/Meis control asymmetric cell divisions in the C. elegans seam stem-like cells by regulating WRM-1/b-catenin localization. Biol. Open 2, 718-727, 2013
Sara Maxwell, Joanne Harding, Charles Brabin, Peter J Appleford, Ruth Brown, Carol Delaney, Garry Brown and Alison Woollard. The SFT-1 and OXA-1 respiratory chain complex factors influence lifespan by distinct mechanisms in C. elegans. Long. Healthspan 2:9, 2013
Promel et al. The GPS motif is a molecular switch for bimodal signaling of the Adhesion-class G protein-coupled receptor LAT-1/Latrophilin. Cell Reports 2,321-31, 2012
Brabin,C., Appleford, P.J. and Woollard, A. The Caenorhabditis elegans GATA factor ELT-1 work through the cell proliferation regulator BRO-1 and the fusogen EFF-1 to maintain the seam stem-like fate. PLoS Genetics 7, e1002200, 2011
Figure 1: Cartoon of seam stem cell division patterns during post-embryonic hermaphrodite development. In males, extra symmetrical divisions in the posterior seam lineages (V5, V6 and T) expand the pool of seam progenitor cells that eventually give rise to male specific neuroblasts, the ray precursor cells. Male specific ray sub-lineages then give rise to nine sensory rays found on each side of the tail
Figure 2: Over-expression of rnt-1 and bro-1 in C. elegans causes hyperplasia of the stem-like seam cells (white nuclei visible). In humans, mis-expression of the rnt-1 and bro-1 homologues Runx and CBFβ are associated with various cancers including Leukaemias. Therefore, worms provide an important model system in which to analyse these genes
Figure 3: Stem-like seam cell expressing rnt-1::gfp (green) in the nucleus and the ajm-1::cherry (red) adherens junction marker outlining the cells