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How to Build a Worm Gut

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The C. elegans embryo shown in the figure has a total of ~ 550 cells, of which ~100 are in the digestive tract.  Every cell in the digestive tract contains either ELT-2 or PHA-4, two transcription factors studied in the McGhee Lab.   "green" = GFP reporter construct driven by the promoter of the gut-specific elt-2 gene.  " red" = Antibody to the PHA-4 protein, present in every cell of the pharynx and rectum.

Our aim is to understand, as completely as possible, the development of the digestive tract of the simple nematode worm Caenorhabditis elegans.  The C. elegans digestive tract, in its simplest description, has three distinct sections: pharynx, intestine (or gut) and rectum.  Approximately two thirds of our efforts is on gut development, about one third on the organogenesis of the pharynx and rectum.  Our emphasis throughout is on transcriptional regulation: what genes are turned on in the various parts of the digestive tract, what genes control them, how is digestive-tract specificity and correct timing of transcription achieved and how is gene expression throughout the entire organ system co-ordinated.  We have every expectation that important factors identified in C. elegans digestive tract formation will have counterparts in the digestive tracts of humans.

We began by studying the regulation of a simple esterase gene called ges-1, which is expressed in every cell of the C. elegans digestive tract.  Regulation of ges-1 shows several interesting and unusual features; for example, regulation centres on a tandem pair of GATA sites in the ges-1 promoter but deletion of these sites causes ges-1 to be expressed in other sections of the digestive tract, indicating a "system-wide" level of gene control.  We have used this observation to approach the mechanism of anterior-posterior patterning within the C. elegans endoderm and to study the evolution of this novel control mechanism in other nematodes.

Most of our work now focuses on two transcription factors that, between them, are expressed in every cell of the C. elegans embryonic digestive tract (see Figure above).  The first factor is a GATA transcription factor called elt-2, which is expressed in every cell of the gut, beginning when the gut has two cells and persisting for the life of the worm; null mutants in elt-2 are lethal.  elt-2 appears homologous to Drosophila serpent and vertebrate GATA4,5,6, other endoderm associated GATA factors.  The second factor is a fork head homolog that we cloned and recently identified with a gene called pha-4, previously shown by others to be necessary for crucial early steps in pharynx and rectum organogenesis.  The questions to be asked are similar for elt-2 and for pha-4: What downstream genes do they control and how do they control them?  What upstream genes control elt-2 and pha-4 and how do they control them?  The experimental approaches range from classical genetic screens, molecular genetic analysis of promoters and the detailed biochemistry of DNA-protein interactions, all with the aim of understanding how genes (and embryos) do what they do.

Our overall view is that knowing how individual transcription factors control individual genes will not be enough to understand gut development.  Rather, it will be necessary to understand how these factors interact within a complex and redundant regulatory network.  We wish to understand how the stable behaviours of such networks give rise to stable "cell fates" and how such networks respond to evolutionary pressure.  The power of C. elegans as an experimental system may actually make it feasible to understand digestive tract development at a satisfying, perhaps even a quantitative level.

Members of the McGhee Lab (2002)

The McGhee Lab
Health Sciences Centre, Rooms 2205 and 2232
Genes and Development Research Group
Department of Biochemistry and Molecular Biology
The University of Calgary
3330 Hospital Drive N.W.
Calgary, Alberta
T2N 4N1

Phone:   (403) 220 4476 (Office)
               (403) 220 3006 (Lab)
Fax:        (403) 270 0737

Email: jmcghee@ucalgary.ca