The C1orf9 gene encodes a putative transmembrane member of a novel protein family

Absence of SUN-domain protein Slp1 blocks karyogamy and switches meiotic recombination and synapsis from homologs to sister chromatids

Karyogamy, the process of nuclear fusion is required for two haploid gamete nuclei to form a zygote. Also, in haplobiontic organisms, karyogamy is required to produce the diploid nucleus/cell that then enters meiosis. We identify sun like protein 1 (Slp1), member of the mid-Sad1p, UNC-84-domain ubiquitous family, as essential for karyogamy in the filamentous fungus Sordaria macrospora, thus uncovering a new function for this protein family. Slp1 is required at the last step, nuclear fusion, not for earlier events including nuclear movements, recognition, and juxtaposition. Correspondingly, like other family members, Slp1 localizes to the endoplasmic reticulum and also to its extensions comprising the nuclear envelope. Remarkably, despite the absence of nuclear fusion in the slp1 null mutant, meiosis proceeds efficiently in the two haploid "twin" nuclei, by the same program and timing as in diploid nuclei with a single dramatic exception: the normal prophase program of recombination and synapsis between homologous chromosomes, including loading of recombination and synaptonemal complex proteins, occurs instead between sister chromatids. Moreover, the numbers of recombination-initiating double-strand breaks (DSBs) and ensuing recombinational interactions, including foci of the essential crossover factor Homo sapiens enhancer of invasion 10 (Hei10), occur at half the diploid level in each haploid nucleus, implying per-chromosome specification of DSB formation. Further, the distribution of Hei10 foci shows interference like in diploid meiosis. Centromere and spindle dynamics, however, still occur in the diploid mode during the two meiotic divisions. These observations imply that the prophase program senses absence of karyogamy and/or absence of a homolog partner and adjusts the interchromosomal interaction program accordingly.

KIAA1096, a gene on chromosome 1q, is amplified and overexpressed in bladder cancer

Chromosomal gain on 1q23-24 is a cytogenetic finding found in approximately 30% of bladder tumors. Currently, no defined or candidate tumor-associated genes from this region have been identified. The objective of this study was to identify and quantitate the expression of putative cancer genes located at this chromosome locus in normal urothelium, superficial, and muscle invasive bladder tumors. We examined both normal and bladder cancer tissue specimens (N = 40-80 RNA, DNA, and protein) by semiquantitative RT/PCR, genomic PCR, and by Western blotting. The KIAA1096 gene is located at 1q23-24 with no overexpression or amplification in normal urothelium, but was significantly upregulated in 30% of tumors (P = 0.0001). There was a trend towards increased expression in invasive compared to superficial lesions (P = 0.06). A significant increase in gene copy was also found in a 38% of TCC of the bladder compared to normal bladder mucosa or peripheral blood lymphocytes. Immunohistochemistry (IHC) demonstrated KIAA1096 expression in nonmalignant bladder mucosa tissue but apparent upregulation in invasive transitional cell carcinoma. Two other genes, CH1 and RGS5, which are situated in the same region of chromosome 1q, demonstrated disparate patterns of expression. In summary, KIAA1096 is a gene situated at 1q23-24, which demonstrated a pattern of RNA and DNA expression consistent with the 38% expression of cytogenetic amplification noted on previous studies. This gene may, therefore, be a putative marker for this cytogenetic phenomenon and provide an opportunity to evaluate the clinical significance of previous cytogenetic findings.