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The role of homeobox genes in defining the axial patterns of the bilateral symmetry of the Acropora millepora (coral) body is studied.

Author(s): Amy E. Pasquinelli [1, 2]; Brenda J. Reinhart [1, 2]; Frank Slack [3]; Mark Q. Martindale [4]; Mitzi I. Kuroda [5]; Betsy Maller [3]; David C. Hayward [6]; Eldon [...]

Considerable attention has recently been focused on the potential involvement of DNA methylation in regulating gene expression in cnidarians. Much of this work has been centered on corals, in the context of changes in methylation perhaps facilitating adaptation to higher seawater temperatures and other stressful conditions. Although first proposed more than 30 years ago, the possibility that DNA methylation systems function in protecting animal genomes against the harmful effects of transposon activity has largely been ignored since that time. Here, we show that transposons are specifically targeted by the DNA methylation system in cnidarians, and that the youngest transposons (i.e. those most likely to be active) are most highly methylated. Transposons in longer and highly active genes were preferentially methylated and, as transposons aged, methylation levels declined, reducing the potentially harmful side effects of CpG methylation. In Cnidaria and a range of other invertebrates, correlation between the overall extent of methylation and transposon content was strongly supported. Present transposon burden is the dominant factor in determining overall level of genomic methylation in a range of animals that diverged in or before the early Cambrian, suggesting that genome defense represents the ancestral role of CpG methylation. [ABSTRACT FROM AUTHOR]

The integrin family of cell surface receptors is strongly conserved in higher animals, but the evolutionary history of integrins is obscure. We have identified and sequenced cDNAs encoding integrin [Beta] subunits from a coral (phylum Cnidaria) and a sponge (Porifera), indicating that these proteins existed in the earliest stages of metazoan evolution. The coral [[Beta].sub.Cn1] and, especially, the sponge [[Beta].sub.o1] sequences are the most divergent of the '[[Beta].sub.1]-class' integrins and share a number of features not found in any other vertebrate or invertebrate integrins. Perhaps the greatest difference from other [Beta] subunits is found in the third and fourth repeats of the cysteine-rich stalk, where the generally conserved spacings between cysteines are highly variable, but not similar, in [[Beta].sub.Cn1] and [[Beta].sub.Po1]. Alternatively spliced cDNAs, containing a stop codon about midway through the full-length translated sequence, were isolated from the sponge library. These cDNAs appear to define a boundary between functional domains, as they would encode a protein that includes the globular ligand-binding head but would be missing the stalk, transmembrane, and cytoplasmic domains. These and other sequence comparisons with vertebrate integrins are discussed with respect to models of integrin structure and function.

We have cloned and characterized the Antennapedia (Antp) gene from the grasshopper Schistocerca americana. The Antennapedia protein contains seven blocks of sequence, including the homeodomain, that are conserved in the homologous proteins of other inserts, interspersed with (usually repetitive) sequences unique to each species. There is no similarity between 1.8 kb of 3' untranslated sequence in grasshopper and Drosophila. We examined Antennapedia protein expression in grasshopper using an antibody raised against a grasshopper fusion protein and reexamined its expression in Drosophila using several different antibodies. Early patterns of expression in the two insects are quite different, reflecting differing modes of early development. However, by the germband stage, expression patterns are quite similar, with relatively uniform epithelial expression throughout the thoracic and abdominal segments which later retracts to the thorax. Expression is observed in muscle pioneers, the peripheral nervous system, and the central nervous system (CNS). In the CNS expression is initially limited to a few neurons, but eventually becomes widespread. Both insects show strong expression in certain homologous identified neurons and similar temporal modulation of expression.