Abstract
The RUNX genes encode conserved transcription factors that play vital roles in the development of various animals and human diseases. Recent studies by a few groups including ours have demonstrated that this gene family, as represented by a single ortholog designeated rnt‐1, also occurs and plays intriguing roles in the simple model organism, Caenorhabditis elegans. Our genetic and molecular analyses revealed that rnt‐1 is allelic to mab‐2, which had previously been known to cause an abnormal development of the male tail. rnt‐1 was further shown to be predominantly expressed in the stem cell‐like lateral seam hypodermal cells. These cells are characterized by their abilities to undergo stem cell‐like asymmetric divisions giving rise to self‐renewing seam cells and various differentiated descendants of hypodermal and neuronal fates. We found that rnt‐1 mutants exhibit an impaired asymmetry in the division of T cells, the posterior‐most member of the seam cells. Mutant analysis indicated that rnt‐1 is involved in regulating T blast cell polarity in cooperation with the Wnt signaling pathway. On the other hand, Nimmo et al. independently discovered that rnt‐1 acts as a rate limiting regulator of cell proliferation in the seam cells, V1‐6. In this review, we will outline these new findings and discuss their general implications in the mechanism of coordination between proliferation and differentiation of stem cells. J. Cell. Biochem. 100: 1119–1130, 2007. © 2007 Wiley‐Liss, Inc.