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1.
Suga H Koyanagi M Hoshiyama D Ono K Iwabe N Kuma K Miyata T 《Journal of molecular evolution》1999,48(6):646-653
To know whether genes involved in cell–cell communication typical of multicellular animals dramatically increased in concert
with the Cambrian explosion, the rapid evolutionary burst in the major groups of animals, and whether these genes exist in
the sponge lacking cell cohesiveness and coordination typical of eumetazoans, we have carried out cloning of the G-protein
α subunit (Gα) and the protein tyrosine kinase (PTK) cDNAs from Ephydatia fluviatilis (freshwater sponge) and Hydra magnipapillata strain 105 (hydra). We obtained 13 Gα and 20 PTK cDNAs. Generally animal gene families diverged first by gene duplication
(subtype duplication) that gave rise to diverse subtypes with different primary functions, followed by further gene duplication
in the same subtype (isoform duplication) that gave rise to isoform genes with virtually identical function. Phylogenetic
trees of Gα and PTK families including cDNAs from sponge and hydra revealed that most of the present-day subtypes had been
established in the very early evolution of animals before the parazoan–eumetazoan split, the earliest branching among the
extant animal phyla, by extensive subtype duplication: for PTK and Gα families, 23 and 9 subtype duplications were observed
in the early stage before the parazoan–eumetazoan split, respectively, and after that split, only 2 and 1 subtype duplications
were found, respectively. After the separation from arthropods, vertebrates underwent frequent isoform duplications before
the fish–tetrapod split. Furthermore, rapid amino acid changes appear to have occurred in concert with the extensive subtype
duplication and isoform duplication. Thus the pattern of gene diversification during animal evolution might be characterized
by bursts of gene duplication interrupted by considerably long periods of silence, instead of proceeding gradually, and there
might be no direct link between the Cambrian explosion and the extensive gene duplication that generated diverse functions
(subtypes) of these families.
Received: 4 November 1998 / Accepted: 17 November 1998 相似文献
2.
Protein tyrosine phosphatases (PTPs) regulate various physiological events in animal cells. They comprise a diverse family
which are classified into two categories, receptor type and nonreceptor type. From the domain organization and phylogenetic
tree, we have classified known PTPs into 17 subtypes (9 receptor-type and 8 nonreceptor-type PTPs) which are characterized
by different organization of functional domain and independent cluster in tree. The receptor type PTPs are thought to be implicated
in cell–cell adhesion by association of cell adhesion molecules. Since sponges are the most primitive multicellular animals
and are thought to be lacking cell cohesiveness and coordination typical of eumetazoans, cloning and sequencing of PTP cDNAs
of Ephydatia fluviatilis (freshwater sponge) have been conducted by RT-PCR to determine whether or not sponges have PTP genes in their genomes. We
have isolated nine PTPs, of which five are possibly receptor type. A phylogenetic tree including the sponge PTPs revealed
that most of the gene duplications that gave rise to the 17 subtypes had been completed in the very early evolution of animals
before the parazoan–eumetazoan split, the earliest branching among extant animal phyla. The family tree also revealed the
rapid evolutionary rate of PTP subtypes in the early stage of animal evolution.
Received: 22 October 1998 / Accepted: 27 November 1998 相似文献
3.
Hiroshi Suga Daisuke Hoshiyama Shigehiro Kuraku Kazutaka Katoh Kaoru Kubokawa Takashi Miyata 《Journal of molecular evolution》1999,49(5):601-608
Animals evolved a variety of gene families involved in cell–cell communication and developmental control by gene duplication
and domain shuffling. Each family is made up of several subtypes or subfamilies with distinct structures and functions, which
diverged by gene duplications and domain shufflings before the divergence of parazoans and eumetazoans. Since the separation
from protostomes, vertebrates expanded the multiplicity of members (isoforms) in the same subfamily by further gene duplications
in their early evolution before the fish–tetrapod split. To know the dates of isoform duplications more closely, we have conducted
isolation and sequencing cDNAs encoding the fibroblast growth factor receptor, Eph, src, and platelet-derived growth factor receptor subtypes belonging to the protein tyrosine kinase family from Branchiostoma belcheri, an amphioxus, Eptatretus burgeri, a hagfish, and Lampetra reissneri, a lamprey. From a phylogenetic tree of each subfamily inferred from a maximum likelihood (ML) method, together with a bootstrap
analysis based on the ML method, we have shown that the isoform duplications frequently occurred in the early evolution of
vertebrates around or just before the divergence of cyclostomes and gnathostomes by gene duplications and possibly chromosomal
duplications.
Received: 28 April 1998 / Accepted: 30 June 1999 相似文献
4.
Aouacheria A Geourjon C Aghajari N Navratil V Deléage G Lethias C Exposito JY 《Molecular biology and evolution》2006,23(12):2288-2302
Collagens are thought to represent one of the most important molecular innovations in the metazoan line. Basement membrane type IV collagen is present in all Eumetazoa and was found in Homoscleromorpha, a sponge group with a well-organized epithelium, which may represent the first stage of tissue differentiation during animal evolution. In contrast, spongin seems to be a demosponge-specific collagenous protein, which can totally substitute an inorganic skeleton, such as in the well-known bath sponge. In the freshwater sponge Ephydatia mülleri, we previously characterized a family of short-chain collagens that are likely to be main components of spongins. Using a combination of sequence- and structure-based methods, we present evidence of remote homology between the carboxyl-terminal noncollagenous NC1 domain of spongin short-chain collagens and type IV collagen. Unexpectedly, spongin short-chain collagen-related proteins were retrieved in nonsponge animals, suggesting that a family related to spongin constitutes an evolutionary sister to the type IV collagen family. Formation of the ancestral NC1 domain and divergence of the spongin short-chain collagen-related and type IV collagen families may have occurred before the parazoan-eumetazoan split, the earliest divergence among extant animal phyla. Molecular phylogenetics based on NC1 domain sequences suggest distinct evolutionary histories for spongin short-chain collagen-related and type IV collagen families that include spongin short-chain collagen-related gene loss in the ancestors of Ecdyzosoa and of vertebrates. The fact that a majority of invertebrates encodes spongin short-chain collagen-related proteins raises the important question to the possible function of its members. Considering the importance of collagens for animal structure and substratum attachment, both families may have played crucial roles in animal diversification. 相似文献
5.
6.
Phylogenetics of Perissodactyla and Tests of the Molecular Clock 总被引:3,自引:0,他引:3
Two mitochondrial genes, the protein-coding cytochrome c oxidase subunit II (COII) gene and a portion of the 12S rRNA gene, were used for phylogenetic investigation of the mammalian
order Perissodactyla. The primary objective of the study was to utilize the extensive fossil record of perissodactyls for
calibrating molecular clocks and comparing estimates of divergence times using both genes and two fossil calibration points.
Secondary objectives included clarification of previously unresolved relationships within Tapiridae and comparison of the
results of separate and combined analyses of two genes. Analyses included several perissodactyl lineages representing all
three families (Tapiridae, Equidae, and Rhinocerotidae), most extant genera, all four species of tapirs, two to four species
of rhinoceros, and two species of Equus. The application of a relatively recent fossil calibration point and a relatively ancient calibration point produced greatly
different estimates of evolutionary rates and divergence times for both genes, even though a relative rates test did not find
significant rate differences among taxa. A likelihood-ratio test, however, rejected a molecular clock for both genes. Neither
calibration point produced estimates of divergence times consistent with paleontological evidence over a range of perissodactyl
radiations. The combined analysis of both genes produces a well-resolved phylogeny with Perissodactyla that conforms to traditional
views of interfamilial relationships and supports monophyly of neotropical tapirs. Combining the data sets increases support
for most nodes but decreases the support for a neotropical tapir clade because the COII and 12S rRNA data sets are in conflict
for tapir relationships.
Received: 6 January 1999 / Accepted: 2 August 1999 相似文献
7.
Jak (Janus kinase) is a nonreceptor tyrosine kinase, which plays important roles in signal transduction pathways. The unique
feature of Jak is that, in addition to a fully functional tyrosine kinase domain (JH1), Jak possesses a pseudokinase domain
(JH2). Although JH2 lost its catalytic function, experimental evidence has shown that this domain may have acquired some new
but unknown functions. This apparent functional divergence after the (internal) domain duplication may result in dramatic
changes of selective constraints at some sites. We conducted a data analysis to test this hypothesis. Our result shows that
shifted selective constraints (or shifted evolutionary rates) between the JH1 and the JH2 domains are statistically significant.
Predicted amino acid sites by posterior analysis can be classified into two groups: very conserved in JH1 but highly variable
in JH2, and vice versa. Moreover, we have studied the evolutionary pattern of four tissue-specific genes, Jak1, Jak2, Jak3, and Tyk2, which were
generated in the early stages of vertebrates. We found that after the (first) gene duplication, site-specific rate shifts
between Jak2/Jak3 and Jak1/Tyk are significant, presumably as a consequence of functional divergence among these genes. The
implication of our study for functional genomics is discussed. 相似文献
8.
Colm O'hUigin Holger Sültmann Herbert Tichy Brent W. Murray 《Journal of molecular evolution》1998,47(5):578-585
We report the cDNA sequences for the DMA and DMB family of Mhc genes of the gray short-tailed opossum. Until now DM sequences were available only in eutherian mammals. The marsupial sequences indicate that both members of the family are
old and probably diverged from other classical class II families about the time of the radiation of jawed vertebrates some
450 million years ago. We examine the evolutionary rates of equivalent sets of classical and nonclassical genes to check for
rate heterogeneity. We find the α-1 domain of the DR genes to be untypically conservative in its evolutionary mode. The DM genes appear to evolve at rates typical of other class II genes, indicating that their placement at the root of class II
gene evolutionary trees may be justified.
Received: 2 March 1998 / Accepted: 2 June 1998 相似文献
9.
10.
Molecular Timing of Primate Divergences as Estimated by Two Nonprimate Calibration Points 总被引:13,自引:0,他引:13
The complete mitochondrial DNA (mtDNA) molecule of the hamadryas baboon, Papio hamadryas, was sequenced and included in a molecular analysis of 24 complete mammalian mtDNAs. The particular aim of the study was to
time the divergence between Cercopithecoidea and Hominoidea. That divergence, set at 30 million years before present (MYBP)
was a fundamental reference for the original proposal of recent hominoid divergences, according to which the split among gorilla,
chimpanzee, and Homo took place 5 MYBP. In the present study the validity of the postulated 30 MYBP dating of the Cercopithecoidea/Hominoidea
divergence was examined by applying two independent nonprimate molecular references, the divergence between artiodactyls and
cetaceans set at 60 MYBP and that between Equidae and Rhinocerotidae set at 50 MYBP. After calibration for differences in
evolutionary rates, application of the two references suggested that the Cercopithecoidea/Hominoidea divergence took place
>50 MYBP. Consistent with the marked shift in the dating of the Cercopithecoidea/Hominoidea split, all hominoid divergences
receive a much earlier dating. Thus the estimated date of the divergence between Pan (chimpanzee) and Homo is 10–13 MYBP and that between Gorilla and the Pan/Homo linage ≈17 MYBP. The same datings were obtained in an analysis of clocklike evolving genes. The findings show that recalculation
is necessary of all molecular datings based directly or indirectly on a Cercopithecoidea/Hominoidea split 30 MYBP.
Received: 1 April 1998 / Accepted: 1 July 1998 相似文献
11.
Debashish Bhattacharya Klaus Weber Seon Sook An Wolfgang Berning-Koch 《Journal of molecular evolution》1998,47(5):544-550
Green algae and land plants trace their evolutionary history to a unique common ancestor. This ``green lineage' is phylogenetically
subdivided into two distinct assemblages, the Chlorophyta and the Streptophyta. The Chlorophyta includes the Chlorophyceae,
Trebouxiophyceae, Ulvophyceae, and Prasinopohyceae, whereas the Streptophyta includes the Charophyceae plus the bryophytes,
ferns, and all other multicellular land plants (Embryophyta). The Prasinophyceae is believed to contain the earliest divergences
within the green lineage. Phylogenetic analyses using rDNA sequences identify the prasinophytes as a paraphyletic taxon that
diverges at the base of the Chlorophyta. rDNA analyses, however, provide ambiguous results regarding the identity of the flagellate
ancestor of the Streptophyta. We have sequenced the actin-encoding cDNAs from Scherffelia dubia (Prasinophyceae), Coleochaete scutata, Spirogyra sp. (Charophyceae), and the single-copy actin gene from Mesostigma viride (Prasinophyceae). Phylogenetic analyses show Mesostigma to be the earliest divergence within the Streptophyta and provide direct evidence for a scaly, biflagellate, unicellular
ancestor for this lineage. This result is supported by the existence of two conserved actin-coding region introns (positions
20-3, 152-1), and one intron in the 5′-untranslated region of the actin gene shared by Mesostigma and the embryophytes.
Received: 10 July 1997 / Accepted: 9 April 1998 相似文献
12.
Michael Kruse Sally P. Leys Isabel M. Müller Werner E.G. Müller 《Journal of molecular evolution》1998,46(6):721-728
Recent analyses of genes encoding proteins typical for multicellularity, especially adhesion molecules and receptors, favor
the conclusion that all metazoan phyla, including the phylum Porifera (sponges), are of monophyletic origin. However, none
of these data includes cDNA encoding a protein from the sponge class Hexactinellida. We have now isolated and characterized
the cDNA encoding a protein kinase C, belonging to the C subfamily (cPKC), from the hexactinellid sponge Rhabdocalyptus dawsoni. The two conserved regions, the regulatory part with the pseudosubstrate site, the two zinc fingers, and the C2 domain, as
well as the catalytic domain were used for phylogenetic analyses. Sequence alignment and construction of a phylogenetic tree
from the catalytic domains revealed that the yeast Saccharomyces cerevisiae and the protozoan Trypanosoma brucei are at the base of the tree, while the hexactinellid R. dawsoni branches off first among the metazoan sequences; the other two classes of the Porifera, the Calcarea (the sequence from Sycon raphanus was used) and the Demospongiae (sequences from Geodia cydonium and Suberites domuncula were used), branch off later. The statistically robust tree also shows that the two cPKC sequences from the higher invertebrates
Drosophila melanogaster and Lytechinus pictus are most closely related to the calcareous sponge. This finding was also confirmed by comparing the regulatory part of the
kinase gene. We suggest, that (i) within the phylum Porifera, the class Hexactinellida diverged first from a common ancestor
to the Calcarea and the Demospongiae, which both appeared later, and (ii) the higher invertebrates are more closely related
to the calcareous sponges.
Received: 6 August 1997 / Accepted: 24 October 1997 相似文献
13.
The evolution of the hedgehog gene family in chordates: insights from amphioxus hedgehog 总被引:9,自引:0,他引:9
Sebastian M. Shimeld 《Development genes and evolution》1999,209(1):40-47
The hedgehog family of intercellular signalling molecules have essential functions in patterning both Drosophila and vertebrate embryos. Drosophila has a single hedgehog gene, while vertebrates have evolved at least three types of hedgehog genes (the Sonic, Desert and
Indian types) by duplication and divergence of a single ancestral gene. Vertebrate Sonic-type genes typically show conserved
expression in the notochord and floor plate, while Desert- and Indian-type genes have different patterns of expression in
vertebrates from different classes. To determine the ancestral role of hedgehog in vertebrates, I have characterised the hedgehog
gene family in amphioxus. Amphioxus is the closest living relative of the vertebrates and develops a similar body plan, including
a dorsal neural tube and notochord. A single amphioxus hedgehog gene, AmphiHh, was identified and is probably the only hedgehog family member in amphioxus, showing the duplication of hedgehog genes to
be specific to the vertebrate lineage. AmphiHh expression was detected in the notochord and ventral neural tube, tissues that express Sonic-type genes in vertebrates. This
shows that amphioxus probably patterns its ventral neural tube using a molecular pathway conserved with vertebrates. AmphiHh was also expressed on the left side of the pharyngeal endoderm, reminiscent of the left-sided expression of Sonic hedgehog in chick embryos which forms part of a pathway controlling left/right asymmetric development. These data show that notochord,
floor plate and possibly left/right asymmetric expression are ancestral sites of hedgehog expression in vertebrates and amphioxus.
In vertebrates, all these features have been retained by Sonic-type genes. This may have freed Desert-type and Indian-type
hedgehog genes from selective constraint, allowing them to diverge and take on new roles in different vertebrate taxa.
Received: 20 July 1998 / Accepted: 23 September 1998 相似文献
14.
Summary. The lancelet (amphioxus), a cephalochordate, is the closest invertebrate relative to vertebrates, with a simple vertebrate-like
body plan and a prototypical genome. We have determined D-aspartic acid (D-Asp) and major free L-amino acids (L-AAs) content
in the nervous system (neural tube) of the European amphioxus Branchiostoma lanceolatum, and have compared these values with those of molluscs and human brain. The B. lanceolatum neural tube contains relatively high amounts of L-Glu, L-Asp, L-Ala and L-Gly. Thus, the amphioxus neural tube has in common
with the molluscan and human nervous systems the presence of appreciable amounts of L-Glu and L-Asp, which suggests that they
are the most common neurotransmitters among these phylogenetically distant animal groups. The relatively high concentration
of L-Ala in amphioxus is consistent with that found in molluscs and the low concentration of taurine is consistent with that
described in the human brain.
The D-Asp concentration, very high in the molluscan nervous system, was rather low in amphioxus, although a little higher
than the extremely low amounts observed in the human brain. Our data on free amino acids composition is in agreement with
the intermediate phylogenetic position of cephalochordates, in terms of the evolutionary transition from simple to complex
neural systems. 相似文献
15.
Thomas A. Gorr Barbara K. Mable Traute Kleinschmidt 《Journal of molecular evolution》1998,47(4):471-485
Phylogenetic relationships among reptiles were examined using previously published and newly determined hemoglobin sequences.
Trees reconstructed from these sequences using maximum-parsimony, neighbor-joining, and maximum-likelihood algorithms were
compared with a phylogenetic tree of Amniota, which was assembled on the basis of published morphological data. All analyses differentiated α chains into αA and αD types, which are present in all reptiles except crocodiles, where only αA chains are expressed. The occurrence of the αD chain in squamates (lizards and snakes only in this study) appears to be a general characteristic of these species. Lizards
and snakes also express two types of β chains (βI and βII), while only one type of β chain is present in birds and crocodiles.
Reconstructed hemoglobin trees for both α and β sequences did not yield the monophyletic Archosauria (i.e., crocodilians + birds) and Lepidosauria (i.e., Sphenodon+ squamates) groups defined by the morphology tree. This discrepancy, as well as some other poorly resolved nodes, might be
due to substantial heterogeneity in evolutionary rates among single hemoglobin lineages. Estimation of branch lengths based
on uncorrected amino acid substitutions and on distances corrected for multiple substitutions (PAM distances) revealed that
relative rates for squamate αA and αD chains and crocodilian β chains are at least twice as high as those of the rest of the chains considered. In contrast to
these rate inequalities between reptilian orders, little variation was found within squamates, which allowed determination
of absolute evolutionary rates for this subset of hemoglobins. Rate estimates for hemoglobins of lizards and snakes yielded
1.7 (αA) and 3.3 (β) million years/PAM when calibrated with published divergence time vs. PAM distance correlates for several speciation
events within snakes and for the squamate ↔ sphenodontid split. This suggests that hemoglobin chains of squamate reptiles
evolved ∼3.5 (αA) or ∼1.7 times (β) faster than their mammalian equivalents. These data also were used to obtain a first estimate of some
intrasquamate divergence times.
Received: 15 September 1997 / Accepted: 4 February 1998 相似文献
16.
Berg OG 《Journal of molecular evolution》1999,48(4):398-407
The synonymous divergence between Escherichia coli and Salmonella typhimurium is explained in a model where there is a large variation between mutation rates at different nucleotide sites in the genome.
The model is based on the experimental observation that spontaneous mutation rates can vary over several orders of magnitude
at different sites in a gene. Such site-specific variation must be taken into account when studying synonymous divergence
and will result in an apparent saturation below the level expected from an assumption of uniform rates. Recently, it has been
suggested that codon preference in enterobacteria has a very large site-specific variation and that the synonymous divergence
between different species, e.g., E. coli and Salmonella, is saturated. In the present communication it is shown that when site-specific variation in mutation rates is introduced,
there is no need to invoke assumptions of saturation and a large variability in codon preference. The same rate variation
will also bring average mutation rates as estimated from synonymous sequence divergence into numerical agreement with experimental
values.
Received: 10 July 1998 / Accepted: 20 August 1998 相似文献
17.
Fernando Alvarez-Valin Kamel Jabbari Nicolas Carels Giorgio Bernardi 《Journal of molecular evolution》1999,49(3):330-342
In this work, we have investigated the relationships between synonymous and nonsynonymous rates and base composition in coding
sequences from Gramineae to analyze the factors underlying the variation in substitutional rates. We have shown that in these genes the rates of nucleotide
divergence, both synonymous and nonsynonymous, are, to some extent, dependent on each other and on the base composition. In
the first place, the variation in nonsynonymous rate is related to the GC level at the second codon position (the higher the
GC2 level, the higher the amino acid replacement rate). The correlation is especially strong with T2, the coefficients being significant in the three data sets analyzed. This correlation between nonsynonymous rate and base
composition at the second codon position is also detectable at the intragenic level, which implies that the factors that tend
to increase the intergenic variance in nonsynonymous rates also affect the intragenic variance. On the other hand, we have
shown that the synonymous rate is strongly correlated with the GC3 level. This correlation is observed both across genes and at the intragenic level. Similarly, the nonsynonymous rate is also
affected at the intragenic level by GC3 level, like the silent rate. In fact, synonymous and nonsynonymous rates exhibit a parallel behavior in relation to GC3 level, indicating that the intragenic patterns of both silent and amino acid divergence rates are influenced in a similar
way by the intragenic variation of GC3. This result, taken together with the fact that the number of genes displaying intragenic correlation coefficients between
synonymous and nonsynonymous rates is not very high, but higher than random expectation (in the three data sets analyzed),
strongly suggests that the processes of silent and amino acid replacement divergence are, at least in part, driven by common
evolutionary forces in genes from Gramineae.
Received: 2 July 1998 / Accepted: 18 April 1999 相似文献
18.
Five cDNAs (pDidact2–pDidact6), representing different actin genes, were isolated from a Diphyllobothrium dendriticum cDNA library, and the DNA as well as the putative amino acid sequences were determined. The corresponding Didact2 and Didact4 genes code for peptides 376 amino acids long, with molecular weights 41,772 and 41,744 Da, respectively, while the deduced
Didact3 protein is 377 amino acids long and weighs 41,912 Da. The pDidact5 and -6 cDNAs lack nucleotides corresponding to three to six amino acids at the amino-terminus. Two of the five cDNAs contain the
conventional AATAAA as the putative polyadenylation signal, one has the common variant ATTAAA, whereas the hexanucleotide
AATAGA is found 15 and 18 nucleotides, respectively, upstream of the poly(A) site in two of the cDNAs. Phylogenetic studies
including 102 actin protein sequences revealed that there are at least four different types of cestode actins. In this study
three of these types were found to be expressed in the adult D. dendriticum tapeworm. Structurally the cestode actin groupings differ from each other to an extent seen only among the metazoan actins
between the vertebrate muscle and cytoplasmic isoforms. In the phylogenetic trees constructed, cestode actins were seen to
map to two different regions, one on the border of the metazoan actins and the other within this group. It is, however, difficult
to say whether the cestode actins branched off early in the metazoan evolution or if this position in the phylogenetic tree
only reflects upon differences in evolutionary rate.
Received: 19 June 1996 / Accepted: 20 August 1996 相似文献
19.
The pairs of nitrogen fixation genes nifDK and nifEN encode for the α and β subunits of nitrogenase and for the two subunits of the NifNE protein complex, involved in the biosynthesis
of the FeMo cofactor, respectively. Comparative analysis of the amino acid sequences of the four NifD, NifK, NifE, and NifN
in several archaeal and bacterial diazotrophs showed extensive sequence similarity between them, suggesting that their encoding
genes constitute a novel paralogous gene family. We propose a two-step model to reconstruct the possible evolutionary history
of the four genes. Accordingly, an ancestor gene gave rise, by an in-tandem paralogous duplication event followed by divergence,
to an ancestral bicistronic operon; the latter, in turn, underwent a paralogous operon duplication event followed by evolutionary
divergence leading to the ancestors of the present-day nifDK and nifEN operons. Both these paralogous duplication events very likely predated the appearance of the last universal common ancestor.
The possible role of the ancestral gene and operon in nitrogen fixation is also discussed.
Received: 21 June 1999 / Accepted: 1 March 2000 相似文献
20.
Molecular Phylogeny of Metazoan Intermediate Filament Proteins 总被引:7,自引:0,他引:7
Andreas Erber Dieter Riemer Marc Bovenschulte Klaus Weber 《Journal of molecular evolution》1998,47(6):751-762
We have cloned cytoplasmic intermediate filament (IF) proteins from a large number of invertebrate phyla using cDNA probes,
the monoclonal antibody IFA, peptide sequence information, and various RT-PCR procedures. Novel IF protein sequences reported
here include the urochordata and nine protostomic phyla, i.e., Annelida, Brachiopoda, Chaetognatha, Echiura, Nematomorpha,
Nemertea, Platyhelminthes, Phoronida, and Sipuncula. Taken together with the wealth of data on IF proteins of vertebrates
and the results on IF proteins of Cephalochordata, Mollusca, Annelida, and Nematoda, two IF prototypes emerge. The L-type,
which includes 35 sequences from 11 protostomic phyla, shares with the nuclear lamins the long version of the coil 1b subdomain
and, in most cases, a homology segment of some 120 residues in the carboxyterminal tail domain. The S-type, which includes
all four subfamilies (types I to IV) of vertebrate IF proteins, lacks 42 residues in the coil 1b subdomain and the carboxyterminal
lamin homology segment. Since IF proteins from all three phyla of the chordates have the 42-residue deletion, this deletion
arose in a progenitor prior to the divergence of the chordates into the urochordate, cephalochordate, and vertebrate lineages,
possibly already at the origin of the deuterostomic branch. Four phyla recently placed into the protostomia on grounds of
their 18S rDNA sequences (Brachiopoda, Nemertea, Phoronida, and Platyhelminthes) show IF proteins of the L-type and fit by
sequence identity criteria into the lophotrochozoic branch of the protostomia.
Received: 2 April 1998 / Accepted: 19 June 1998 相似文献