Regulated nuclear entry of the C-elegans Pax-6 transcription factor

It is shown that the C. elegans Pax-6 locus encodes two protein isoforms. O ne contains a Paired DNA binding domain as well as a homeodomain; the other consists only of the carboxy-terminal portion of the locus encoding the ho meodomain. These two isoforms are expressed in a variety of postembryonic c ell lineages. In one set of lineages, nuclear localization of a homeodomain -only form (MAB-18 isoform) appears to be under temporal and spatial contro l. Nuclear localization of MAB-18 is correlated with the genetic requiremen t for mab-18 and with activation of a reporter gene driven by a mab-18 prom oter, Reporter gene expression is dependent on mab-18 gene activity. It is hypothesized that a positive feedback loop is activated by regulated nuclea r entry. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.