Figure 1. HIM-18 is a conserved protein that localizes in both mitotic and late meiotic prophase germline nuclei. (A) Schematic representation of the predicted HIM-18 protein structure. The region deleted in the
tm2181 mutant allele is indicated (codons 161 through 277). The various conserved domains are indicated by the following abbreviations: ZF, zinc finger; CC, coiled coil; BTB, Bric-a-brac, Tramtrack, Broad-complex; SAP, SAF-A/B, Acinus and PIAS; LZ, leucine zipper. The black bar indicates the N-terminal region used for antibody production. (B) Schematic representation of Caenorhabditis elegans HIM-18 and related predicted proteins in Homo sapiens, Mus musculus, Drosophila melanogaster, Saccharomyces cerevisiae, and Schizosaccharomyces pombe. Protein names and accession numbers are indicated. Percent identity and similarity (I and S, respectively) are indicated in parentheses. The brown horizontal bar indicates the region of homology in Dm-MUS312 shared with Sc-Slx4. (C) Immunolocalization of HIM-18 in germline nuclei of wild type hermaphrodites. Low magnification images show nuclei progressing from the premeiotic tip through all the stages of meiotic prophase, in a left to right orientation. Arrowheads indicate the beginning of transition zone and entrance into meiosis. A single focal plane from a representative nucleus of each stage is shown at a higher magnification. Detection thresholds for anti-HIM-18 signals in transition zone and mid-pachytene panels were lower than for other panels to permit imaging of the lower levels of chromosome-associated HIM-18 observed in these stages. Bars, 20 um for whole gonad, 1 um in insets.