Nicole Saad, Hiroshi Kagoshima, and Alison Woollard.
rnt-1 is the C. elegans orthologue of the Runx family of transcriptional regulators implicated in various human cancers. There are three Runx genes in humans; Runx1 is associated with acute myeloid leukaemia and is thought to act both as an oncogene and as a tumour suppressor. Runx2 is associated with cleidocranial dysplasia and Runx3 is postulated to be associated with gastric cancer. Previous work in the lab has identified
rnt-1 as the defective gene in
mab-2 mutants. Mab mutants have defects in the formation of the male tail, arising from seam cell lineages.
mab-2/rnt-1 mutants have missing rays because there is a reduction in the number of ray precursor cells. The reduction in ray precursor cell number is a direct consequence of a reduction in the number of seam cells. The reduction in seam cell number in
rnt-1 mutants is usually the result of a failure in particular cell divisions. Overexpressing
rnt-1 results in an increase in seam cell number. This is compelling evidence that
rnt-1 is a rate limiting regulator of cell proliferation.. The CBFbeta orthologue
bro-1 has a similar function to
rnt-1 in regulating seam cell proliferation.
bro-1 deletion alleles have reduced numbers of seam cells and are missing rays in the male tail.
bro-1 animals have similar cell proliferation defects to
rnt-1 animals. CBFbeta has also been linked with leukaemia, and been shown to act as a binding partner for Runx factors. We are currently investigating
bro-1 further. We would now like to explore whether over expression of
bro-1 results in seam cell hyperplasia, and whether a synergistic effect is seen if
rnt-1 and
bro-1 are co-overexpressed. We are also testing whether
rnt-1-induced seam cell hyperplasia is dependent on
bro-1 function.. In order to assess the conservation of the Runx genes we are currently pursuing complementation experiments using mouse Runx cDNAs. Expression will be driven in worms using both the endogenous worm promoter and the
hsp16.2 heatshock promoter to see if it is able to complement the function of the worm orthologue. We are also making transgenic worms expressing mammalian CBFbeta along with Runx1, Runx2 or Runx3, and testing these combinations for rescue of a
rnt-1 mutant and induction of hyperplasia. C. elegans
bro-1 is much more highly diverged from CBFbeta than
rnt-1 is from Runx genes, therefore it is possible that mammalian Runx proteins will not function in C. elegans in the absence of CBFbeta. Therefore, we will also test interactions between
bro-1 and mammalian Runx genes in yeast two-hybrid assays. We hope to present results from these experiments at the meeting.