To explore the scope and significance of alternate promoter usage and its putative inter-relationship to alternative splicing, we searched expression sequence tags for the 5 region of acetylcholinesterase (ACHE) genes. Three and five novel first exons were identified in human and mouse ACHE genes, respectively. Reverse transcription-PCR and in situ hybridization validated most of the predicted transcripts, and sequence analyses of the corresponding genomic DNA regions suggest evolutionarily conserved promoters for each of the novel exons identified. Distinct tissue specificity and stress-related expression patterns of these exons predict combinatorial complexity with known 3 alternative AChE mRNA transcripts. Unexpectedly one of the 5 exons encodes an extended N terminus in-frame with the known AChE sequence, extending the increased complexity to the protein level. The resultant membrane variant(s), designated N-AChE, is developmentally regulated in human brain neurons and blood mononuclear cells. Alternative promoter usage combined with alternative splicing may thus lead to stress-dependent combinatorial complexity of AChE mRNA transcripts and their protein products.Alternative splicing and alternate promoter usage both expand the complexity of gene products. While the massive contribution of alternative splicing to such expansion is widely recognized (1), less is known about the scope and significance of alternate promoter usage. Moreover the directionality of transcription processes raises the yet unresolved possibility that these two phenomena are inter-related, namely that the choice of the first exon determines downstream splice choices (2). The recent accumulation of genomic and gene expression data bases together with the development of sophisticated bioinformatic tools makes these questions amenable for experimental analysis as multiple gene products display both alternate promoter usage and alternative splicing variations. By alignment of expression sequence tags (ESTs) 1 against genomic sequences, for example, it is possible to explore the different alternatively spliced products of a single gene (3, 4). However, EST data bases are biased toward the 3Ј end of mRNAs and occasionally contain genomic contaminations that may cause misinterpretation of the genomic information (5). To correctly evaluate the inter-relationship between alternate promoter usage and alternative splicing, it is therefore necessary to characterize the identified variants using traditional molecular biology tools at the RNA level and, if applicable, at the protein level as well.The acetylcholine-hydrolyzing enzyme acetylcholinesterase (AChE) provides an adequate example for such a study. AChE pre-mRNA is subject to stimulus-induced 3Ј alternative splicing (6), and previous evidence has suggested that it is also subject to alternate promoter usage (7,8). We analyzed the genomic regions flanking the human and mouse ACHE genes and found an unexpected, evolutionarily conserved diversity of alternate exons at their 5Ј end. The newly id...

Gill bacterial communities of Chama pacifica, an Indo-Pacific invasive oyster to the eastern Mediterranean Sea, were compared with those of Chama savignyi, its northern Red Sea congeneric species. Summer and winter bacterial populations were characterized and compared using 16S rDNA clone libraries, and seasonal population dynamics were monitored by automated ribosomal intergenic spacer analysis (ARISA). Clone libraries revealed a specific clade of bacteria, closely related to marine endosymbionts from the Indo-Pacific, found in both ecosystems, of which one taxon was conserved in oysters from both sites. This taxon was dominant in summer libraries and was weakly present in winter ones, where other members of this group were dominant. ARISA results revealed significant seasonal variation in bacterial populations of Mediterranean Sea oysters, as opposed to Red Sea ones that were stable throughout the year. We suggest that this conserved association between bacteria and oyster reflects either a symbiosis between the oyster host and some of its bacteria, a co-invasion of both parties, or both.

The Indo‐Pacific oyster Chama pacifica Broderip, 1835 (Mollusca, Bivalvia, Chamidae) is rarely found in the Northern Red Sea reefs of Eilat (Gulf of Aqaba), where it is outnumbered by its indigenous congener, Chama savignyi Lamy, 1921. The influx of Eritrean biota from the Red Sea into the Mediterranean Sea via the Suez Canal has led to the formation of massive Chama oyster beds along the Eastern Mediterranean shore. However, unlike the Northern Red Sea, the Eastern Mediterranean Chama beds are dominated by C. pacifica oysters, whereas C. savignyi is absent from this region. In an attempt to understand this difference in their respective distribution, the reproductive biology of both species was compared. Histological analysis of the male and female gonads, monitored monthly from March 2009 to August 2010 in both regions, revealed a similar reproductive cycle, comprising six stages: onset of gametogenesis, advanced gametogenesis, ripe, ready to spawn, spent and sexual rest. Female gonads demonstrated an additional, seventh stage – restoration, coinciding with inferred spawning of ripe gametes. Both species were found to be dioecious spawners, with a single, annual, temperature‐dependent inferred spawning period. Chama pacifica was found to reproduce efficiently in maximal Mediterranean seawater temperatures not experienced by the Northern Red Sea Chama populations. This study demonstrates the high invasive potential of an oyster species despite its rarity in its source region.

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