Cryptocyanin, a crustacean molting protein: evolutionary link with arthropod hemocyanins and insect hexamerins.
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Cryptocyanin, a copper-free hexameric protein in crab (Cancer magister) hemolymph, has been characterized and the amino acid sequence has been deduced from its cDNA. It is markedly similar in sequence, size, and structure to hemocyanin, the copper-containing oxygen-transport protein found in many arthropods. Cryptocyanin does not bind oxygen, however, and lacks three of the six highly conserved copper-binding histidine residues of hemocyanin. Cryptocyanin has no phenoloxidase activity, although a phenoloxidase is present in the hemolymph. The concentration of cryptocyanin in the hemolymph is closely coordinated with the molt cycle and reaches levels higher than hemocyanin during premolt. Cryptocyanin resembles insect hexamerins in the lack of copper, molt cycle patterns of biosynthesis, and potential contributions to the new exoskeleton. Phylogenetic analysis of sequence similarities between cryptocyanin and other members of the hemocyanin gene family shows that cryptocyanin is closely associated with crustacean hemocyanins and suggests that cryptocyanin arose as a result of a hemocyanin gene duplication. The presence of both hemocyanin and cryptocyanin in one animal provides an example of how insect hexamerins might have evolved from hemocyanin. Our results suggest that multiple members of the hemocyanin gene family-hemocyanin, cryptocyanin, phenoloxidase, and hexamerins-may participate in two vital functions of molting animals, oxygen binding and molting. Cryptocyanin may provide important molecular data to further investigate evolutionary relationships among all molting animals. (+info)
Molecular studies suggest that cartilaginous fishes have a terminal position in the piscine tree.
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The Chondrichthyes (cartilaginous fishes) are commonly accepted as being sister group to the other extant Gnathostomata (jawed vertebrates). To clarify gnathostome relationships and to aid in resolving and dating the major piscine divergences, we have sequenced the complete mtDNA of the starry skate and have included it in phylogenetic analysis along with three squalomorph chondrichthyans-the common dogfish, the spiny dogfish, and the star spotted dogfish-and a number of bony fishes and amniotes. The direction of evolution within the gnathostome tree was established by rooting it with the most closely related non-gnathostome outgroup, the sea lamprey, as well as with some more distantly related taxa. The analyses placed the chondrichthyans in a terminal position in the piscine tree. These findings, which also suggest that the origin of the amniote lineage is older than the age of the oldest extant bony fishes (the lungfishes), challenge the evolutionary direction of several morphological characters that have been used in reconstructing gnathostome relationships. Applying as a calibration point the age of the oldest lungfish fossils, 400 million years, the molecular estimate placed the squalomorph/batomorph divergence at approximately 190 million years before present. This dating is consistent with the occurrence of the earliest batomorph (skates and rays) fossils in the paleontological record. The split between gnathostome fishes and the amniote lineage was dated at approximately 420 million years before present. (+info)
Coalescent estimates of HIV-1 generation time in vivo.
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The generation time of HIV Type 1 (HIV-1) in vivo has previously been estimated using a mathematical model of viral dynamics and was found to be on the order of one to two days per generation. Here, we describe a new method based on coalescence theory that allows the estimate of generation times to be derived by using nucleotide sequence data and a reconstructed genealogy of sequences obtained over time. The method is applied to sequences obtained from a long-term nonprogressing individual at five sampling occasions. The estimate of viral generation time using the coalescent method is 1.2 days per generation and is close to that obtained by mathematical modeling (1.8 days per generation), thus strengthening confidence in estimates of a short viral generation time. Apart from the estimation of relevant parameters relating to viral dynamics, coalescent modeling also allows us to simulate the evolutionary behavior of samples of sequences obtained over time. (+info)
Evolutionary relationships among diverse bacteriophages and prophages: all the world's a phage.
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We report DNA and predicted protein sequence similarities, implying homology, among genes of double-stranded DNA (dsDNA) bacteriophages and prophages spanning a broad phylogenetic range of host bacteria. The sequence matches reported here establish genetic connections, not always direct, among the lambdoid phages of Escherichia coli, phage phiC31 of Streptomyces, phages of Mycobacterium, a previously unrecognized cryptic prophage, phiflu, in the Haemophilus influenzae genome, and two small prophage-like elements, phiRv1 and phiRv2, in the genome of Mycobacterium tuberculosis. The results imply that these phage genes, and very possibly all of the dsDNA tailed phages, share common ancestry. We propose a model for the genetic structure and dynamics of the global phage population in which all dsDNA phage genomes are mosaics with access, by horizontal exchange, to a large common genetic pool but in which access to the gene pool is not uniform for all phage. (+info)
A glycyl radical site in the crystal structure of a class III ribonucleotide reductase.
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Ribonucleotide reductases catalyze the reduction of ribonucleotides to deoxyribonucleotides. Three classes have been identified, all using free-radical chemistry but based on different cofactors. Classes I and II have been shown to be evolutionarily related, whereas the origin of anaerobic class III has remained elusive. The structure of a class III enzyme suggests a common origin for the three classes but shows differences in the active site that can be understood on the basis of the radical-initiation system and source of reductive electrons, as well as a unique protein glycyl radical site. A possible evolutionary relationship between early deoxyribonucleotide metabolism and primary anaerobic metabolism is suggested. (+info)
Expression pattern of Brachyury and Not in the sea urchin: comparative implications for the origins of mesoderm in the basal deuterostomes.
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This work concerns the expression of two transcription factors during the development of the sea urchin Strongylocentrotus purpuratus: SpNot, the orthologue of the vertebrate Not gene, and SpBra, the orthologue of the vertebrate Brachyury gene. SpNot transcripts are detected by in situ hybridization in the vegetal plate at the mesenchyme-blastula stage. Later the gene is expressed in the secondary mesenchyme, but expression is no longer detectable after gastrulation. SpNot is upregulated during larval development, in the invaginating vestibule of the adult rudiment. Transcripts are also found in several larva-specific tissues, including the epaulets, blastocoelar cells, and pigment cells. SpBra also displays a discontinuous pattern of expression. Much like SpNot, this gene is expressed during embryogenesis in the embryonic vegetal plate and secondary mesenchyme founder cells, and expression is then extinguished. The gene is upregulated over a week later in the feeding larva, in the vestibule of the adult rudiment. In contrast to SpNot, SpBra is also expressed in the mesoderm of both left and right hydrocoels, and it is not expressed in any larva-specific tissues. We compare the spatial expression profile determined in this study with that of the orthologous Brachyury gene in an indirectly developing enteropneust hemichordate, a representative of the sister group to the echinoderms within the deuterostomes. These observations illuminate the genetic basis underlying the process of maximal indirect development in basal deuterostomes. Finally, Brachyury appears to be an excellent marker for the progeny of the set-aside cells of the sea urchin embryo. (+info)
Evolution of visual pigments in geckos.
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Most geckos are nocturnal forms and possess rod retinas, but some diurnal genera have pure-cone retinas. We isolated cDNAs encoding the diurnal gecko opsins, dg1 and dg2, similar to nocturnal gecko P521 and P467, respectively. Despite the large morphological differences between the diurnal and nocturnal gecko photoreceptor types, they express phylogenetically closely related opsins. These results provide molecular evidence for the reverse transmutation, that is, rods of an ancestral nocturnal gecko have backed into cones of diurnal geckos. The amino acid substitution rates of dgl and dg2 are higher than those of P521 and P467, respectively. Changes of behavior regarding photic environment may have contributed to acceleration of amino acid substitutions in the diurnal gecko opsins. (+info)
Cellular localization and evolution of prolactin receptor mRNA in ovine endometrium during pregnancy.
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In this study, we have investigated the expression of the prolactin receptor gene in ovine endometrium during oestrus cycle and pregnancy. Using reverse transcription-PCR analysis, we provided evidence that the prolactin receptor gene is specifically transcribed in this tissue. As shown by Northern blot analysis, the level of the prolactin receptor transcripts increased dramatically during late pregnancy. In situ hybridization experiments revealed that prolactin receptor mRNA was specifically expressed in the glandular compartment and confirmed the dramatic increase of its expression that occurs at the end of pregnancy. Taken together, these findings are consistent with a putative role of prolactin and/or related molecules in the regulation of the proliferation of the glandular compartment and/or in the control of the secretory activity of the endometrium. (+info)