Ancient origin of the Hox gene cluster.

The Hox gene cluster has a crucial function in body patterning during animal development. How and when this gene cluster originated is being clarified by recent data from Cnidaria, a basal animal phylum. The characterization of Hox-like genes from Hydra, sea anemones and jellyfish has revealed that a Hox gene cluster is extremely ancient, having originated even before the divergence of these basal animals.

Phospholipase C cDNAs from sponge and hydra: antiquity of genes involved in the inositol phospholipid signaling pathway.

To know whether or not the set of genes involved in the inositol phospholipid signaling pathway already existed in the early evolution of animals, we carried out cloning of cDNAs encoding phospholipase Cs (PLCs) from Ephydatia fluviatilis (freshwater sponge) and Hydra magnipapillata strain 105 (hydra). We isolated two PLC cDNAs, PLC-betaS and PLC-gammaS, from sponge and three cDNAs, PLC-betaH1, PLC-betaH2, and PLC-deltaH, from hydra. From the domain organization and the divergence pattern in the PLC family tree, the sponge PLC-betaS and PLC-gammaS and the hydra PLC-deltaH are possibly homologous to the vertebrate PLC-beta, PLC-gamma and PLC-delta subtypes, respectively. A detailed phylogenetic analysis suggests that the hydra PLC-betaH1 and PLC-betaH2 are homologs of the vertebrate PLC-beta1/2/3/Drosophila PLC21 and the vertebrate PLC-beta4/Drosophila norpA, respectively. A phylogenetic analysis of the PLC family and the protein kinase C (PKC) family, together with that of the G protein alpha subunit (Galpha) family, revealed that the origin of the set of genes G(alpha)q, PLC, PKC involved in the inositol phospholipid signaling pathway is very old, going back to dates before the parazoan-eumetazoan split, the earliest branching among extant animal phyla.

Dangers in the ocean: the traveler and marine envenomation. I. jellyfish.

Envenomation by marine creatures is more common than is often realized, and regularly accounts for both death and severe morbidity in humans. Worldwide marine envenomation morbidity and mortality result from two main animal groups: (1) jellyfish, and (2) "other" marine animals. Venomous jellyfish are discussed in part I of this article, with relevant information on their distribution and appearance, and on symptoms of envenomation; first aid and medical treatment are also suggested.

Homology of Hox genes and the zootype concept in early metazoan evolution.

The correct identification of homologous Hox genes within and between diplo- and triploblastic animals is of crucial importance for recent hypotheses on the anagenetic evolution of animal bauplans. While the homology discussion in general has reached new heights, we apply traditional homology criteria to assign homology to Hox genes from diploblastic animals. Comparison of the Trox-2 gene from the presumably most basal metazoan animal, the placozoan Trichoplax adhaerens, to other Hox genes suggests the presence of unambiguous homologs in Hydrozoa and Scyphozoa and the absence of any specific homolog in triploblasts. Furthermore, the comparisons provide support for the idea that Hox genes-at least in diploblastic animals-are composed of functional subunits (modules), which to some degree have undergone independent evolution. The findings are not readily compatible with the existence of the "zootype" in diploblastic animals.

Evolution of paired domains: isolation and sequencing of jellyfish and hydra Pax genes related to Pax-5 and Pax-6.

Pax proteins are a family of transcription factors with a highly conserved paired domain; many members also contain a paired-type homeodomain and/or an octapeptide. Nine mammalian Pax genes are known and classified into four subgroups: Pax-1/9, Pax-2/5/8, Pax-3/7, and Pax-4/6. Most of these genes are involved in nervous system development. In particular, Pax-6 is a key regulator that controls eye development in vertebrates and Drosophila. Although the Pax-4/6 subgroup seems to be more closely related to Pax-2/5/8 than to Pax-3/7 or Pax-1/9, its evolutionary origin is unknown. We therefore searched for a Pax-6 homolog and related genes in Cnidaria, which is the lowest phylum of animals that possess a nervous system and eyes. A sea nettle (a jellyfish) genomic library was constructed and two pax genes (Pax-A and -B) were isolated and partially sequenced. Surprisingly, unlike most known Pax genes, the paired box in these two genes contains no intron. In addition, the complete cDNA sequences of hydra Pax-A and -B were obtained. Hydra Pax-B contains both the homeodomain and the octapeptide, whereas hydra Pax-A contains neither. DNA binding assays showed that sea nettle Pax-A and -B and hydra Pax-A paired domains bound to a Pax-5/6 site and a Pax-5 site, although hydra Pax-B paired domain bound neither. An alignment of all available paired domain sequences revealed two highly conserved regions, which cover the DNA binding contact positions. Phylogenetic analysis showed that Pax-A and especially Pax-B were more closely related to Pax-2/5/8 and Pax-4/6 than to Pax-1/9 or Pax-3/7 and that the Pax genes can be classified into two supergroups: Pax-A/Pax-B/Pax-2/5/8/4/6 and Pax-1/9/3/7. From this analysis and the gene structure, we propose that modern Pax-4/6 and Pax-2/5/8 genes evolved from an ancestral gene similar to cnidarian Pax-B, having both the homeodomain and the octapeptide.