The Runt gene family is a new family of heteromeric DNA binding transcription factors. Recent work has revealed that members of this family play  important roles in embryonic development of sea urchin, segmentation of Drosophila, and hematopoiesis and osteoblast differntiation in mouse and human. The heteromeric complex consists of two subunits, a DNA binding subunit aand its partner subunit b. The a subunit binds directly to a specific DNA sequence (PuCCPuCAG [Pu=A/G]) while theb subunit associates with ato form a heterodimer that has a greater affinity for DNA. The asubunit shares a region of high homology, termed the Runt domain (Fig. 1), with the products of the Drosophila segmentation gene runt and the human acute myeloid leukemia-related gene AML1. A series of biochemical analyses revealed that the Runt domain is sufficient for both functions of the asubunit: DNA binding and heterodimerization with the bsubunit. In mammals, there are 3 types of asubunits, aA,aB and aC. Targeted disruption of aA in mouse results in a complete lack of ossification in their skeletal systems. The human homolog of aB, AML1, is known as the most frequent target of chromosomal translocations associated with leukemia, and targeted mice lacking AML1 showed no fetal liver hematopoiesis. aB has thus proved to be essential for hematopoiesis of all lineages. We found a C. elegans homolog of runt by searching in the C. elegans databases, which we propose to call rnt-1. We made a promoter-gfp-lacZ reporter construct to examine the temporal and spatial expression pattern.  We observed gfp expression in the hypodermis, the seam and probably their precursor cells starting from the 2-fold stage embryo to adult. This result implied that rnt-1 might have quite different functions in different organisms, which contrasts with the high sequence conservation. Moreover, so far  no bsubunit gene has been found in C. elegans; this subunit has important regulatory functions for the Runt domain. To elucidate the function of rnt-1 in worms, we are going to do RNAi experiments and screen knock-out mutant libraries. This should give us new insights into the function of this gene family.  

Affiliation:
- Biozentrum der Universität Basel, Klingelbergstrasse 70,4056 Basel, Switzerland