Here we report the genome sequence of the honeybee Apis mellifera, a key model for social behaviour and essential to global ecology through pollination. Compared with other sequenced insect genomes, the A. mellifera genome has high A+T and CpG contents, lacks major transposon families, evolves more slowly, and is more similar to vertebrates for circadian rhythm, RNA interference and DNA methylation genes, among others. Furthermore, A. mellifera has fewer genes for innate immunity, detoxification enzymes, cuticle-forming proteins and gustatory receptors, more genes for odorant receptors, and novel genes for nectar and pollen utilization, consistent with its ecology and social organization. Compared to Drosophila, genes in early developmental pathways differ in Apis, whereas similarities exist for functions that differ markedly, such as sex determination, brain function and behaviour. Population genetics suggests a novel African origin for the species A. mellifera and insights into whether Africanized bees spread throughout the New World via hybridization or displacement.

DNA methylation systems are well characterized in vertebrates, but methylation in Drosophila melanogaster and other invertebrates remains controversial. Using the recently sequenced honey bee genome, we present a bioinformatic, molecular, and biochemical characterization of a functional DNA methylation system in an insect. We report on catalytically active orthologs of the vertebrate DNA methyltransferases Dnmt1 and Dnmt3a and b, two isoforms that contain a methyl-DNA binding domain, genomic 5-methyl-deoxycytosine, and CpG-methylated genes. The honey bee provides an opportunity to study the roles of methylation in social contexts.

The transcription factors Snail, Slug, and bHLH E47 have been recently described as direct repressors of E-cadherin and inducers of epithelial-mesenchymal transition (EMT) and invasion when overexpressed in epithelial cells. Although a role of those factors in tumor progression and invasion has been proposed, whether the different repressors play distinct or redundant roles in the tumorigenic process has not been established. To further investigate this important issue, we have analyzed the gene expression profiling of MadinDarby canine kidney (MDCK) epithelial cells expressing the different repressors (MDCK-Snail, MDCK-Slug, and MDCK-E47 cells) versus control MDCK cells by cDNA microarrays. A total of 243 clones (228 genes and 15 expressed sequence tags) were found to be differentially expressed between either of the three MDCK-derived cell lines and control MDCK cells. Twenty two of the candidate genes were validated by Northern blot, Western blot, immunofluorescence, and promoter analyses in cell lines and by immunohistochemistry in xenografted tumors. Gene clustering analysis indicated that about a third of the 243 candidate genes were common to MDCK cells expressing Snail, Slug, or E47 factors, whereas the rest of the genes were regulated in only one or two cell types. Differentially regulated genes include those related to EMT (45 genes), transcriptional regulation (18 genes), cell proliferation and signaling (54 genes), apoptosis (12 genes), and angiogenesis (9 genes). These results indicate that Snail, Slug, and E47 transcription factors induce common and specific genetic programs, supporting a differential role of the factors in tumor progression and invasion. (Cancer Res 2006; 66(19): 9543-56)

Overexpression of the transcription factor Snail in epithelial MDCK cells promotes the epithelial-mesenchymal transition (EMT) and the acquisition of an invasive phenotype. We report here that the expression of Snail is associated with an increase in the promoter activity and expression of the matrix metalloproteinase MMP-9. The effect of Snail silencing on MMP-9 expression corroborates this finding. Induced transcription of MMP-9 by Snail is driven by a mechanism dependent on the MAPK and phosphoinositide 3-kinase (PI3K) signalling pathways. Although other regions of the promoter were required for a complete stimulation by Snail, a minimal fragment (nucleotides -97 to +114) produces a response following an increased phosphorylation of Sp-1 and either Sp-1 or Ets-1 binding to the GC-box elements contained in this region. The expression of a dominant negative form of MEK decreased these complexes. A moderate increase in the binding of the nuclear factor κB (NFκB) to the upstream region (nucleotide -562) of the MMP-9 promoter was also observed in Snail-expressing cells. Interestingly, oncogenic H-Ras (RasV12) synergistically co-operates with Snail in the induction of MMP-9 transcription and expression. Altogether, these results indicate that MMP-9 transcription is activated in response to Snail expression and that it might explain, at least in part, the invasive properties of the Snail-expressing cells.