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41.
Sea urchin Hox genes: insights into the ancestral Hox cluster 总被引:3,自引:0,他引:3
We describe the Hox cluster in the radially symmetric sea urchin and
compare our findings to what is known from clusters in bilaterally
symmetric animals. Several Hox genes from the direct-developing sea urchin
Heliocidaris erythrogramma are described. CHEF gel analysis shows that the
Hox genes are clustered on a < or = 300 kilobase (kb) fragment of DNA,
and only a single cluster is present, as in lower chordates and other
nonvertebrate metazoans. Phylogenetic analyses of sea urchin, amphioxus,
Drosophila, and selected vertebrate Hox genes confirm that the H.
erythrogramma genes, and others previously cloned from other sea urchins,
belong to anterior, central, and posterior groups. Despite their radial
body plan and lack of cephalization, echinoderms retain at least one of the
anterior group Hox genes, an orthologue of Hox3. The structure of the
echinoderm Hox cluster suggests that the ancestral deuterostome had a Hox
cluster more similar to the current chordate cluster than was expected Sea
urchins have at least three Abd-B type genes, suggesting that Abd-B
expansion began before the radiation of deuterostomes.
相似文献
42.
The 18S ribosomal RNAs of 21 tetrapods were sequenced and aligned with five
published tetrapod sequences. When the coelacanth was used as an outgroup,
Lissamphibia (living amphibians) and Amniota (amniotes) were found to be
statistically significant monophyletic groups. Although little resolution
was obtained among the lissamphibian taxa, the amniote sequences support a
sister-group relationship between birds and mammals. Portions of the 28S
ribosomal RNA (rRNA) molecule in 11 tetrapods also were sequenced, although
the phylogenetic results were inconclusive. In contrast to previous
studies, deletion or down- weighting of base-paired sites were found to
have little effect on phylogenetic relationships. Molecular evidence for
amniote relationships is reviewed, showing that three genes
(beta-hemoglobin, myoglobin, and 18S rRNA) unambiguously support a
bird-mammal relationship, compared with one gene (histone H2B) that favors
a bird- crocodilian clade. Separate analyses of four other genes (alpha-
crystallin A, alpha-hemoglobin, insulin, and 28S rRNA) and a combined
analysis of all sequence data are inconclusive, in that different groups
are defined in different analyses and none are strongly supported. It is
suggested that until sequences become available from a broader array of
taxa, the molecular evidence is best evaluated at the level of individual
genes, with emphasis placed on those studies with the greatest number of
taxa and sites. When this is done, a bird-mammal relationship is most
strongly supported. When regarded in combination with the morphological
evidence for this association, it must be considered at least as plausible
as a bird-crocodilian relationship.
相似文献
43.
The quantitative immunological technique of micro-complement fixation (MC'F) has been routinely used during the past decade to assess evolutionary relationships among living vertebrate species. The large data base that has been generated, along with the excellent correlations between immunologically measured genetic distances and paleontologically derived estimates of divergence times, have formed the basis for the albumin molecular clock. Immunological distance (ID) involves a logarithmic transformation of experimentally measured antibody concentrations. The justification for this transformation has rested entirely on empirical correlations. Consequently, several other transformations have been proposed as giving better fits to particular data sets. We derive, from first principles, the relationship between ID and the amino acid sequence replacements (AAR) between compared albumins. ID is shown to be a linear estimator of AAR. This ID-AAR relationship is based on a proposed process of antibody assortment and exclusion. We present experimental data confirming that such an antibody assortment-exclusion process occurs in MC'F. This process can explain both the high sensitivity and the quantitative phylogenetic nature of the MC'F assay. The assortment-exclusion process also predicts a divergence limit beyond which MC'F data no longer provide robust phylogenetic data. 相似文献
44.
Interspecific hybrids of the sea urchins Strongylocentrotus purpuratus (♀) and Lytechinus pictus (♂) were used to estimate the contributions of the maternal and paternal genomes to histone mRNA synthesis during early development. Radiolabeled histone mRNAs from the two sea urchin species were identified by hybridization to cloned histone genes from both S. purpuratus and L. pictus and shown to be electrophoretically distinguishable. The synthesis of maternal and paternal histone mRNA in these hybrid embryos is evident as early as the two-cell stage. By at least the 16-cell stage, both maternal and paternal histone mRNAs are associated with polysomes. The relative amounts of the maternal and paternal histone mRNAs synthesized by the zygote appear to be similar. 相似文献
45.
Human rhinoviruses attach to specific receptors located on the surfaces of host cells as a first step in viral infection. A 90-kDa cell surface protein was previously shown to be involved in the attachment of human rhinoviruses to susceptible cells (Tomassini, J. E., and Colonno, R.J. (1986) J. Virol. 58, 290-295). Digestion of purified receptor protein with various glycosidases revealed that 30% of its molecular mass was comprised of complex-type oligosaccharides, one-third being contributed by sialic acid. The presence of sialic acid was confirmed by demonstrating that wheat germ lectin can inhibit the attachment of rhinoviruses to host cell membranes, while lectins of other sugar specificities had no effect. The oligosaccharides were shown to be N-linked by tunicamycin treatment of host cells and by N-glycanase digestion. Seven N-linked glycosylation sites were detected by partial digestion of the receptor oligosaccharides with N-glycanase. Native receptor protein had an isoelectric focusing point of 4.2, compared to 5.3 for the deglycosylated protein. Studies of virus and antibody binding to neuraminidase-treated host cell membranes suggested that although carbohydrates may be involved in host-virus interaction, the receptor carbohydrate is not the predominant component of the cellular receptor site. 相似文献
46.
We have examined the molecular mechanisms responsible for the shifts in histone protein phenotype during embryogenesis in the sea urchinStrongylocentrotus purpuratus. The H1, H2A, and H2B classes of histone synthesized at the earliest stages of cleavage are heterogeneous: These proteins are replaced at late embryogenesis by a different set of histone-like polypeptides, some of which are also heterogeneous. The H3 and H4 histones appear to be homogeneous classes and remain constant. We have isolated from both early and late embryos the individual messenger RNAs coding for each of the multiple protein subtypes. The RNAs were isolated by hybridization to cloned DNA segments coding for a single histone protein or by elution from polyacrylamide gels. Each RNA was then analyzed and identified by its mobility on polyacrylamide gels and by its template activity in the wheat germ cell-free protein synthesizing system. The mRNAs for each of the five early histone protein classes are heterogeneous in size and differ from the late stage templates. The late mRNAs consist of at least 11 separable types coding for the 5 classes of histones. Each of the 11 has been separated and identified. The late stage proteins were shown to be authentic histones since many of their templates hybridize with histone coding DNA. The early and late stage mRNAs are transcribed from different sets of histone genes since (1) late stage H1 and H2A mRNAs fail to hybridize to cloned early stage histone genes under ideal conditions for detecting homologous early stage hybrids, (2) late stage H2B, H3, and H4 RNA/DNA hybrids melt at 14, 11, and 11°C lower, respectively, than do homologous RNA/DNA hybrids, and (3) purified late stage mRNAs direct the synthesis of the variant histone proteins which are synthesized only during later stages. The time course of synthesis of the late stage mRNAs suggests that they appear many hours before the late histone proteins can be detected, possibly as early as fertilization. In addition, early mRNAs are synthesized in small quantities as late as 40 hr after fertilization, during gastrulation. Thus, the major modulations of histone gene expression are neither abrupt nor an absolute on-off switch, and may represent only a gradual and relative repression of early gene expression. Two histones are detected only transiently during early cleavage. The mRNA for one of them, a subtype of H2A, can be detected in the cytoplasm for as long as 40 hr after fertilization. However, template activity for the other, a subtype of H2B, can be detected only at the blastula stage. Thus, the histone genes represent a complex multigene family that is developmentally modulated. 相似文献
47.
Nucleotide sequences of portions of the mitochondrial 12S and 16S ribosomal RNA genes were used to extend a recent study of anuran phylogeny (Hayet al., Mol. Biol. Evol.12: 928–937, 1995) and to further evaluate phylogenetic relationships within the Neobatrachia. An analysis of almost 900 nucleotides from each of 8 new representatives of the Dendrobatidae, Hylidae, Leptodactylidae, and Myobatrachidae, plus 14 available members of the Neobatrachia provides support for 2 major lineages (Bufonoidea and Ranoidea) within this anuran suborder. The neotropical Bufonoidea and their derivatives are monophyletic. There is an interesting association of the 2 Australian myobatrachids with the South African Heleophrynidae, and the Sooglossidae is one of the basal bufonoid lineages. Within the New World bufonoid frogs, a monophyletic Dendrobatidae is strongly supported. An Australian hylid (Pelodryadinae) shows close affinity with the South American hylid Phyllomedusinae. A group composed of Hylinae (HylaandSmilisca), Centrolenidae, Bufonidae, and the hylid Hemiphractinae, with the latter two clustered, was supported significantly. The addition of new taxa has more clearly defined some relationships within the suborder Neobatrachia and has indicated that the families Hylidae, Leptodactylidae, and Myobatrachidae may not be monophyletic. 相似文献
48.
Pancreatic polypeptide and the sister group of birds. 总被引:1,自引:0,他引:1
49.
50.
Thérèse S Lapperre Jacob K Sont Annemarie van Schadewijk Margot ME Gosman Dirkje S Postma Ingeborg M Bajema Wim Timens Thais Mauad Pieter S Hiemstra 《Respiratory research》2007,8(1):85-9