A preliminary comparative analysis of primate segmental duplications shows elevated substitution rates and a great-ape expansion of intrachromosomal duplications

Compared with other sequenced animal genomes, human segmental duplications appear larger, more interspersed, and disproportionately represented as high-sequence identity alignments. Global sequence divergence estimates of human duplications have suggested an expansion relatively recently during hominoid evolution. Based on primate comparative sequence analysis of 37 unique duplication-transition regions, we establish a molecular clock for their divergence that shows a significant increase in their effective substitution rate when compared with unique genomic sequence. Fluorescent in situ hybridization (FISH) analyses from 1053 random nonhuman primate BACs indicate that great-ape species have been enriched for interspersed segmental duplications compared with representative Old World and New World monkeys. These findings support computational analyses that show a 12-fold excess of recent (>98%) intrachromosomal duplications when compared with duplications between nonhomologous chromosomes. These architectural shifts in genomic structure and elevated substitution rates have important implications for the emergence of new genes, gene-expression differences, and structural variation among humans and great apes.     

Genotoxicity of vanadium compounds in yeast and cultured mammalian cells.

The ability of vanadium compounds to induce genetic activity was investigated in D7 and D61M strains of Saccharomyces cerevisiae and in Chinese hamster V79 cell line. In our previous work, ammonium metavanadate (pentavalent form, V5) induced mitotic gene conversion and point reverse mutation in the D7 strain of yeast. The genotoxicity was reduced by the presence of S9 fraction, which probably reduced pentavalent vanadium to the tetravalent form. In the present study, vanadyl sulfate (tetravalent form, V4) induced no convertants and revertants in yeast cells harvested from stationary growth phase. With yeast cells from logarithmic growth phase, which contain high levels of cytochrome P-450, a significant increase in genetic effects was observed. Further experiments, performed by treating cells harvested from logarithmic growth phase in the presence of cytochrome P-450 inhibitors, indicated that the monooxygenase system influenced the genotoxicity of metavanadate while the genetic activity of vanadyl remained unaffected. Aneuploidy effect in the D61M strain of Saccharomyces cerevisiae was induced by either V5 or V4, confirming that vanadium compounds are potentially antitubulin agents in eukaryotic cells. Although these compounds are very toxic in V79 cells, no mutagenic effect was observed in the presence or in the absence of S9 fraction.     

Could EMA and cytokeratin 7 be useful in distinguishing tricholemmal carcinoma from clear-cell squamous cell carcinoma? A case series from our department and a brief review of the literature

Tricholemmal carcinoma is a malignant cutaneous adnexal tumor showing outer root sheath differentiation, thought to be the malignant counterpart of trichilemmoma. Although the real existence of tricholemmal carcinoma continues to be a matter of debate, it has been introduced in the recently published 4th edition of World Health Organization classification of skin tumors. Herein, we evaluated whether immunohistochemistry (EMA, CK7, CK5/14, p63, p16, and Ber-EP4) supports tricholemmal carcinoma as a separate entity and whether it could be useful in this differential diagnosis. A total of 9 cases, 3 tricholemmal carcinomas and 6 clear-cell squamous cell carcinomas were evaluated on the basis of histological criteria suggested by the WHO. In our opinion, although these results need to be validated in larger series, they support tricholemmal carcinoma as a separate entity and suggest an immunohistochemical profile (clear-cell squamous cell carcinomas: EMA diffusely positive, CK7 negative; tricholemmal carcinoma: EMA negative, CK7 patchy or moderately positive) that could be useful for this differential diagnosis.     

Characterization of antigenic peptides presented by HLA-B44 molecules on tumor cells expressing the gene MAGE-3

The amino acid sequence of the protein encoded by the gene MAGE-3was screened for peptides containing the binding motif for HLA-B44. Nine peptides were synthesized, and their binding affinity for HLA-B*4402 and -B*4403 was analyzed in an HLA class I α-chain refolding assay. Four peptides with binding affinity for HLA-B*4403 were chosen for in vitro cytotoxic T-lymphocyte induction assays using as antigen-presenting cells peptide-pulsed, autologous activated B lymphoblasts from a healthy, B*4403⁺ donor. Peptide-specific effectors could be raised only against one peptide, M3-167. Cytotoxic T lymphocytes specific for this peptide were also able to recognize melanoma cell lines expressing HLA-B44 and the gene MAGE-3, strongly suggesting that M3-167is a naturally processed MAGE-3-encoded epitope presented by HLA-B44.M3-167 is a 1 amino acid N-terminal extension of M3-168, a naturally processed epitope MAGE-3-encoded epitope presented by HLA-A1 that has been previously described. TAP binding studies of these 2 peptides revealed that the TAP affinity of M3-167 is about 9-fold higher than that of M3-168. M3-167 or a longer precursor could be transported into the endoplasmatic reticulum, where it could be trimmed for presentation by HLA-A1 or -B44 molecules. Taken together, our data suggest that M3-167 could be an immunodominant peptide encoded by the gene MAGE-3. © 1996 Wiley-Liss, Inc.