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Genome evolution in Arabidopsis/Brassica: conservation and divergence of ancient rearranged segments and their breakpoints.

Since the tetraploidization of the Arabidopsis thaliana ancestor 30-35 million years ago (Mya), a wave of chromosomal rearrangements have modified its genome architecture. The dynamics of this process is unknown, as it has so far been impossible to date individual rearrangement events. In this paper, we present evidence demonstrating that the majority of rearrangements occurred before the Arabidopsis-Brassica split 20-24 Mya, and that the segmental architecture of the A. thaliana genome is predominantly conserved in Brassica. This finding is based on the conservation of four rearrangement breakpoints analysed by fluorescence in situ hybridization (FISH) and RFLP mapping of three A. thaliana chromosomal regions. For this purpose, 95 Arabidopsis bacterial artificial chromosomes (BACs) spanning a total of 8.25 Mb and 81 genetic loci for 36 marker genes were studied in the Brassica oleracea genome. All the regions under study were triplicated in the B. oleracea genome, confirming the hypothesis of Brassica ancestral genome triplication. However, whilst one of the breakpoints was conserved at one locus, it was not at the two others. Further comparison of their organization may indicate that the evolution of the hexaploid Brassica progenitor proceeded by several events, separated in time. Genetic mapping and reprobing with rDNA allowed assignment of the regions to particular Brassica chromosomes. Based on this study of regional organization and evolution, a new insight into polyploidization/diploidization cycles is proposed.

Arabidopsis↗

Alpha-tubulin from early-diverging eukaryotic lineages and the evolution of the tubulin family.

The tubulin gene family, which includes alpha-,beta-, and gamma-tubulin subfamilies, is composed of highly conserved proteins which are the principle structural and functional components of eukaryotic microtubules. We are interested in (1) establishing when in eukaryotic evolution the duplications leading to paralogous alpha, beta, and gamma subfamilies occurred and (2) the possible utility of tubulin sequences in reconstructing organismal phylogeny. To broaden the taxonomic representation of alpha-tubulins so that it roughly equals that of beta-tubulins, alpha-tubulin genes from three Microsporidia (Encephalitozoon hellem, Nosema locustae, and Spraguea lophii), two Parabasalia (Monocercomonas sp. and Trichomitus batrachorum), and one Heterolobosean (Acrasis rosea) were sequenced. With these new genes, phylogenetic trees of alpha- and beta-tubulins were constructed and compared. Trees were congruent with each other, but incongruent with other molecular phylogenies. The agreement between alpha- and beta-tubulin trees could arise by the co-adaptation of one molecule to variants of the other as a result of their intimate steric association in microtubules. Thus, these trees may not be providing independent support for the phylogenetic results. However, one of these unexpected results, that microsporidia cluster with fungi, is supported by other circumstantial evidence, and may therefore reflect a real relationship despite the basal position usually assigned to microsporidia. Relationships between the three tubulins were also examined by constructing trees of all three types. These trees were found to be of limited value for determining the position of the root within each subfamily because of the great interfamily distances, but they do confirm the classification of all known genes into three monophyletic subfamilies. Divergent genes from Caenorhabditis elegans and Saccharomyces cerevisiae that have been proposed to represent the novel classes delta- and epsilon-tubulin were found to be specifically related to gamma-tubulins from animals and fungi respectively, and therefore are best seen as rapidly evolving orthologues of gamma-tubulin.

Amino Acid Sequence↗

Interordinal relationships and timescale of eutherian evolution as inferred from mitochondrial genome data.

Extensive phylogenetic analyses of the updated sequence data of mammalian mitochondrial genomes were carried out using the maximum likelihood method in order to resolve deep branchings in eutherian evolution. The divergence times in the mammalian tree were estimated by a relaxed molecular clock of the mitochondrial proteins calibrated with multiple references. A Chiroptera/Eulipotyphla (i.e. bat/mole) clade and a close relationship of this clade to Fereuungulata (Carnivora+Perissodactyla+Cetartiodactyla) were reconfirmed with high statistical significance. However, a support for a monophyly of Fereuungulata relative to the Chiroptera/Eulipotyphla clade was fragile, and we suggest that the three branchings among Carnivora, Perissodactyla, Cetartiodactyla and Chiroptera/Eulipotyphla occurred successively in a short time period, estimated to be approximately 77Myr BP. The Chiroptera/Eulipotyphla divergence was estimated to roughly coincide with the Cretaceous-Tertiary boundary (65Myr BP). The monophyly of Rodentia, the Lagomorpha/Rodentia clade (traditionally called Glires), and the Afrotheria/Xenarthra clade were preferred over alternative relationships, but the supports of these clades were not strong enough to exclude other possibilities. Although several super-order taxa of eutherians were strongly supported by the analyses of the mitochondrial genome data, the branching order in the deepest part of the eutherian tree remained ambiguous from the data presently available.

Animals↗

Multiple gene duplication and rapid evolution in the groEL gene: functional implications.

The chaperonins, GroEL and GroES, are present ubiquitously and provide a paradigm in the understanding of assisted protein folding. Due to its essentiality of function, GroEL exhibits high sequence conservation across species. Complete genome sequencing has shown the occurrence of duplicate or multiple copies of groEL genes in bacteria such as Mycobacterium tuberculosis and Corynebacterium glutamicum. Monophyly of each bacterial clade in the phylogenetic tree generated for the GroEL protein suggests a lineage-specific duplication. The duplicated groEL gene in Actinobacteria is not accompanied by the operonic groES despite the presence of upstream regulatory elements. Our analysis suggests that in these bacteria the duplicated groEL genes have undergone rapid evolution and divergence to function in a GroES-independent manner. Evaluation of multiple sequence alignment demonstrates that the duplicated genes have acquired mutations at functionally significant positions including those involved in substrate binding, ATP binding, and GroES binding and those involved in inter-ring and intra-ring interactions. We propose that the duplicate groEL genes in different bacterial clades have evolved independently to meet specific requirements of each clade. We also propose that the groEL gene, although essential and conserved, accumulates nonconservative substitutions to exhibit structural and functional variations.

Adenosine Triphosphate↗

Evolutionary origin of the feather epidermis.

The formation of scales and feathers in reptiles and birds has fascinated biologists for decades. How might the developmental processes involved in the evolution of the amniote ectoderm be interpreted to shed light on the evolution of integumental appendages? An Evo-Devo approach to this question is proving essential to understand the observation that there is homology between the transient embryonic layers covering the scale epidermis of alligators and birds and the epidermal cell populations of embryonic feather filaments. Whereas the embryonic layers of scutate scales are sloughed off at hatching, that their homologues persist in feathers demonstrates that the predecessors of birds took advantage of the ability of their ectoderm to generate embryonic layers by recruiting them to make the epidermis of the embryonic feather filament. Furthermore, observations on mutant chickens with altered scale and feather development (Abbott and Asmundson [1957] J. Hered. 18:63-70; Abbott [1965] Poult. Sci. 44:1347; Abbott [1967] Methods in developmental biology. New York: Thomas Y. Crowell) suggest that the ectodermal placodes of feathers, which direct the formation of unique dermal condensations and subsequently appendage outgrowth, provided the mechanism by which the developmental processes generating the embryonic layers diverged during evolution to support the morphogenesis of the epidermis of the primitive feather filament with its barb ridges.

Alligators and Crocodiles↗

Characterization of the three HERV-H proviruses with an open envelope reading frame encompassing the immunosuppressive domain and evolutionary history in primates.

The HERV-H family is one of the largest human endogenous retrovirus families, with approximately 1000 elements. Using a direct coupled in vitro transcription/translation approach (PTT for protein truncation test) and an extended series of primers on human genomic DNA, on monochromosomal hybrids and on a BAC library, we could demonstrate that there are only three envelopes with a large open reading frame encompassing the immunosuppressive (ISU) domain, corresponding to 62-, 60-, and 59-kDa potential translational products. The associated proviruses, HERV-H/env62, HERV-H/env60, and HERV-H/env59 were sequenced together with their flanking DNA and mapped by FISH, and their entry times within the primate lineage were determined. Analysis of the LTR sequences revealed numerous recombinational and/or homogenization events in the course of evolution, with divergences between 5' and 3' LTRs higher than expected for a simple time-dependent genetic drift. PTT analyses further revealed that the three large envelopes in humans are prematurely stopped in the majority of primates, and sequencing of the largest envelope gene, from HERV-H/env62, in five human individuals revealed two polymorphic sites. The results are consistent with the absence of a strong selective pressure for the conservation of a functional envelope gene of possible benefit for the host, but do not exclude somatic effects possibly associated with the immunosuppressive domain carried by these genes.

Animals↗

Molecular evolution of two paralogous tandemly repeated heterochromatic gene clusters linked to the X and Y chromosomes of Drosophila melanogaster.

Here we report the peculiarities of molecular evolution and divergence of paralogous heterochromatic clusters of the testis- expressed X-linked Stellate and Y-linked Su(Ste) tandem repeats. It was suggested that Stellate and Su(Ste) clusters affecting male fertility are the amplified derivatives of the unique euchromatic gene betaCK2tes encoding the putative testis-specific beta-subunit of protein kinase CK2. The putative Su(Ste)-like evolutionary intermediate was detected on the Y chromosome as an orphon outside of the Su(Ste) cluster. The orphon shows extensive homology to the Su(Ste) repeat, but contains several Stellate-like diagnostic nucleotide substitutions, as well as a 10-bp insertion and a 3' splice site of the first intron typical of the Stellate unit. The orphon looks like a pseudogene carrying a drastically damaged Su(Ste) open reading frame (ORF). The putative Su(Ste) ORF, as compared with the Stellate one, carries numerous synonymous substitutions leading to the major codon preference. We conclude that Su(Ste) ORFs evolved on the Y chromosome under the pressure of translational selection. Direct sequencing shows that the efficiency of concerted evolution between adjacent repeats is 5-10 times as high in the Stellate heterochromatic cluster on the X chromosome as that in the Y-linked Su(Ste) cluster, judging by the frequencies of nucleotide substitutions and single-nucleotide deletions.

Animals↗

Internal gene duplication in the evolution of prokaryotic transmembrane proteins.

We investigated the evolution of transmembrane (TM) topology by detecting partial sequence repeats in TM protein sequences and analyzing them in detail. A total of 377 sequences that seem to have evolved by internal gene duplication events were found among 38,124 predicted TM protein sequences (except for single-spannings) from 87 prokaryotic genomes. Various types of internal duplication patterns were identified in these sequences. The majority of them are diploid-type (including quasi-diploid-type) duplication in which a primordial protein sequence was duplicated internally to become an extant TM protein with twice as many TM segments as the primordial one, and the remaining ones are partial duplications including triploid-type. The diploid-type repeats are recognized in many 8-tms, 10-tms and 12-tms TM protein sequences, suggesting the diploid-type duplication was a principle mechanism in the evolutionary development of these types of TM proteins. The "positive-inside" rule is satisfied in whole sequences of both 10-tms and 8-tms TM proteins and in both halves of 10-tms proteins while not necessarily in the second half of 8-tms proteins, providing fit examples of "internal divergent topology evolution" likely occurred after a diploid-type internal duplication event. From analyzing the partial duplication patterns, several evolutionary pathways were recognized for 6-tms TM proteins, i.e. from primordial 2-tms, 3-tms and 4-tms TM proteins to extant 6-tms proteins. Similarly, the duplication pattern analysis revealed plausible evolution scenarios that 7-tms TM proteins have arisen from 3-tms, 4-tms and 5-tms TM protein precursors via partial internal gene duplications.

Amino Acid Sequence↗

Evolution and assembly of Anopheles aquasalis's immune genes: primary malaria vector of coastal Central and South America and the Caribbean Islands.

Anophelines are vectors of malaria, the deadliest disease worldwide transmitted by mosquitoes. The availability of genomic data from various Anopheles species allowed evolutionary comparisons of the immune response genes in search of alternative vector control of the malarial parasites. Now, with the Anopheles aquasalis genome, it was possible to obtain more information about the evolution of the immune response genes. Anopheles aquasalis has 278 immune genes in 24 families or groups. Comparatively, the American anophelines possess fewer genes than Anopheles gambiae s. s., the most dangerous African vector. The most remarkable differences were found in the pathogen recognition and modulation families like FREPs, CLIP and C-type lectins. Even so, genes related to the modulation of the expression of effectors in response to pathogens and gene families that control the production of reactive oxygen species were more conserved. Overall, the results show a variable pattern of evolution in the immune response genes in the anopheline species. Environmental factors, such as exposure to different pathogens and differences in the microbiota composition, could shape the expression of this group of genes. The results presented here will contribute to a better knowledge of the Neotropical vector and open opportunities for malaria control in the endemic-affected areas of the New World.

Animals↗

Chromosomal evolution of the Canidae. II. Divergence from the primitive carnivore karyotype.

The Giemsa-banding patterns of chromosomes from the arctic fox (Alopex lagopus), the red fox (Vulpes vulpes), the kit fox (Vulpes macrotis), and the raccoon dog (Nyctereutes procyonoides) are compared. Despite their traditional placement in different genera, the arctic fox and the kit fox have an identical chromosome morphology and G-banding pattern. The red fox has extensive chromosome arm homoeology with these two species, but has only two entire chromosomes in common. All three species share some chromosomes with the raccoon dog, as does the high diploid-numbered grey wolf (Canis lupus, 2n = 78). Moreover, some chromosomes of the raccoon dog show partial or complete homoeology with metacentric feline chromosomes which suggests that these are primitive canid chromosomes. We present the history of chromosomal rearrangements within the Canidae family based on the assumption that a metacentric-dominated karyotype is primitive for the group.

Animals↗

The pattern of segment formation, as revealed by engrailed expression, in a centipede with a variable number of segments.

Arthropods vary enormously in segment number, from less than 20 to more than 200. This between-species variation must have originated, in evolution, through divergent selection operating in ancestral arthropod species with variable segment numbers. Although most present-day arthropod species are invariant in this respect, some are variable and so can serve as model systems. Here, we describe a study based on one such species, the coastal geophilomorph centipede Strigamia maritima. We investigate the way in which segments are formed using in situ hybridization to demonstrate the expression pattern of the engrailed gene during embryogenesis. We also analyze segment number data in mother-offspring broods and thereby demonstrate a significant heritable component of the variation. We consider how natural selection might act on this intraspecific developmental variation, and we discuss the similarities and differences in segment formation between the geophilomorphs and their phylogenetic sister-group.

Animals↗

Genetics and the origin of bird species.

External (environmental) factors affecting the speciation of birds are better known than the internal (genetic) factors. The opposite is true for several groups of invertebrates, Drosophila being the outstanding example. Ideas about the genetics of speciation in general trace back to Dobzhansky who worked with Drosophila. These ideas are an insufficient guide for reconstructing speciation in birds for two main reasons. First, speciation in birds proceeds with the evolution of behavioral barriers to interbreeding; postmating isolation usually evolves much later, perhaps after gene exchange has all but ceased. As a consequence of the slow evolution of postmating isolating factors the scope for reinforcement of premating isolation is small, whereas the opportunity for introgressive hybridization to influence the evolution of diverging species is large. Second, premating isolation may arise from nongenetic, cultural causes; isolation may be affected partly by song, a trait that is culturally inherited through an imprinting-like process in many, but not all, groups of birds. Thus the genetic basis to the origin of bird species is to be sought in the inheritance of adult traits that are subject to natural and sexual selection. Some of the factors involved in premating isolation (plumage, morphology, and behavior) are under single-gene control, most are under polygenic control. The genetic basis of the origin of postmating isolating factors affecting the early development of embryos (viability) and reproductive physiology (sterility) is almost completely unknown. Bird speciation is facilitated by small population size, involves few genetic changes, and occurs relatively rapidly.

Animals↗

Structure, function and evolution of the Archaeal class I fructose-1,6-bisphosphate aldolase.

FBPA (fructose-1,6-bisphosphate aldolase) catalyses the reversible aldol condensation of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate to form fructose 1,6-bisphosphate. Two classes of FBPA, which rely on different reaction mechanisms, have so far been discovered, class I mainly found in Eucarya and class II mainly in Bacteria. Only recently were genes encoding proteins with FBPA activity identified in Archaea. Archaeal FBPAs do not share any significant overall sequence identity with members of the traditional classes of FBPAs, raising the interesting question of whether they have evolved independently by convergent evolution or diverged from a common ancestor. Biochemical characterization of FBPAs of the two hyperthermophilic Archaea Thermoproteus tenax and Pyrococcus furiosus showed that the enzymes use a Schiff-base mechanism and thus belong to the class I aldolases. The crystal structure of the archaeal FBPA from T. tenax revealed that the protein fold, as for the classical FBPA I and II, is that of a parallel (betaalpha)(8) barrel. A substrate-bound crystal structure allowed detailed active-site comparisons which showed the conservation of six important catalytic and substrate-binding residues between the archaeal and the classical FBPA I. This observation provides further evidence that the two sequence families of proteins share a common evolutionary origin. Furthermore, structure and sequence analysis indicate that the class I FBPA shares a common evolutionary origin with several other enzyme superfamilies of the (betaalpha)(8) barrel fold.

Aeropyrum↗

Evolution of Lycopodiaceae (Lycopsida): estimating divergence times from rbcL gene sequences by use of nonparametric rate smoothing.

By use of nonparametric rate smoothing and nucleotide sequences of the rbcL gene, divergence times in Lycopodiaceae are estimated. The results show that much extant species diversity in Lycopodiaceae stems from relatively recent cladogenic events. These results corroborate previous ideas based on paleobotanical and biogeographical data. Previous molecular phylogenetic analyses recognized a split into neotropical and paleotropical clades in Huperzia, which contains 85-90% of all living species. Connecting this biogeographical pattern with continent movements, the diversification of this epiphytic group was suggested to coincide with that of angiosperms in the mid to Late Cretaceous. Results presented here are consistent with this idea, and the diversification of the two clades is resolved as Late Cretacous (78 and 95 Myr). In the related genera Lycopodium and Lycopodiella, the patterns are somewhat different. Here species diversity is scattered among different subgeneric groups. Most of the high-diversity subgeneric groups seem to have diversified very recently (Late Tertiary), whereas the cladogenic events leading to these groups are much older (Early to Late Cretaceous). Our analysis shows that, although much living species diversity stems from relatively recent cladogenesis, the origins of the family (Early Carboniferous) and generic crown groups (Early Permian to Early Jurassic) are much more ancient events.

Evolution, Molecular↗

Somatosensory cortex of prosimian Galagos: physiological recording, cytoarchitecture, and corticocortical connections of anterior parietal cortex and cortex of the lateral sulcus.

Compared with our growing understanding of the organization of somatosensory cortex in monkeys, little is known about prosimian primates, a major branch of primate evolution that diverged from anthropoid primates some 60 million years ago. Here we describe extensive results obtained from an African prosimian, Galago garnetti. Microelectrodes were used to record from large numbers of cortical sites in order to reveal regions of responsiveness to cutaneous stimuli and patterns of somatotopic organization. Injections of one to several distinguishable tracers were placed at physiologically identified sites in four different cortical areas to label corticortical connections. Both types of results were related to cortical architecture. Three systematic representations of cutaneous receptors were revealed by the microelectrode recordings, S1 proper or area 3b, S2, and the parietal ventral area (PV), as described in monkeys. Strips of cortex rostral (presumptive area 3a) and caudal (presumptive area 1-2) to area 3b responded poorly to tactile stimuli in anesthetized galagos, but connection patterns with area 3b indicated that parallel somatosensory representations exist in both of these regions. Area 3b also interconnected somatotopically with areas S2 and PV. Areas S2 and PV had connections with areas 3a, 3b, 1-2, each other, other regions of the lateral sulcus, motor cortex (M1), cingulate cortex, frontal cortex, orbital cortex, and inferior parietal cortex. Connection patterns and recordings provided evidence for several additional fields in the lateral sulcus, including a retroinsular area (Ri), a parietal rostral area (PR), and a ventral somatosensory area (VS). Galagos appear to have retained an ancestral preprimate arrangement of five basic areas (S1 proper, 3a, 1-2, S2, and PV). Some of the additional areas suggested for lateral parietal cortex may be primate specializations.

Animals↗

High throughput mutation screening of the factor VIII gene (F8C) in hemophilia A: 37 novel mutations and genotype-phenotype correlation.

Hemophilia A (HEMA) is an X-linked bleeding disorder caused by mutations in the factor VIII gene (F8C). Molecular genetic testing for the factor VIII gene is challenging due to its large size. Here we present results of high throughput mutation scanning based on Southern blot analysis and direct sequencing of all PCR amplified coding exons and the exon-intron boundaries of the factor VIII gene. The results of mutation analysis on 89 hemophiliac males showed presence of a disease-causing mutation in 80 individuals (90%, 95% CI of 82%-95%). Seven out of nine mutation-negative individuals were severe cases of hemophilia A with < 1% factor VIII protein in the blood. The correlation of phenotype with genotype as observed in this study was not absolute. This finding is supported by similar observations in the international database for hemophilia A mutations (HAMSTeRS). This issue raises the importance of genotypes at other loci that can act as modifiers for the phenotype. Thirty-four novel mutations and three novel substitutions for previously reported amino acid residues were identified in this series of 80 mutations. The mutations cover the full spectrum including rearrangements, deletions, frameshift, and point mutations. The novel missense mutations require careful evaluation. Prediction of a mutation as the disease-causing allele was made from the nature of the substitution and the degree of conservation of the mutated amino acid among species that have diverged in evolution. In some cases segregation analysis of the mutation with disease condition was performed when other family members were available.

Child↗

The structure and complete nucleotide sequence of the human cyclophilin 40 (PPID) gene.

Cyclophilin 40 is a recently identified member of the cyclophilin family that is found in an unactivated steroid hormone receptor complex. Cyclophilin 40 possesses a region homologous to FKBP59, a member of the FK506-binding protein family that is also a component of the receptor complex. We report the isolation and sequencing of the entire human cyclophilin 40 (hCyP40) gene (human gene symbol PPID). The gene contains 10 exons (43 to 698 bp) and 9 introns encompassing 14.2 kb. The exon organization of the cyclophilin-like region is not similar to that of the human cyclophilin A gene (PPIA), suggesting their early divergence in evolution. Determination of the sequence of the 5' end of the hCyP40 mRNA by an "anchor-ligation PCR" procedure showed that transcription is initiated from a cluster of sites about 80 bp upstream from the first in-frame ATG. The immediate 5'-flanking region of the gene lacks typical TATA and CAAT boxes, but is GC-rich and contains Sp1 sites, features characteristic of promoters associated with housekeeping genes. The hCyP40 gene was mapped to chromosome 4 by PCR with genomic DNA from somatic cell hybrids. As shown by "Zoo blot" analysis, the cyclophilin 40 gene appears to be highly conserved throughout evolution.

Amino Acid Isomerases↗

Three-dimensional solution structure of bombyxin-II an insulin-like peptide of the silkmoth Bombyx mori: structural comparison with insulin and relaxin.

The three-dimensional solution structure of bombyxin-II, an insulin-like two-chain peptide produced by the brain of the silkworm Bombyx mori, has been determined by simulated annealing calculations based on 535 distance constraints and 24 torsion-angle constraints derived from NMR data and three distance constraints of the disulfide bonds. To our knowledge, this is the first three-dimensional structure determined for an invertebrate insulin-related peptide. The root-mean-square deviations between the best 10 structures and the mean structure are 0.58(+/- 0.15) A for the backbone heavy atoms (N, C alpha, C) and 1.03(+/- 0.18) A for all non-hydrogen atom if less well-defined N and C termini (A1, A20, B(-2) to B4 and B23 to B25) are excluded. The overall main-chain structure of bombyxin-II is similar to that of insulin. However, there are significant conformational and functional differences in their B-chain C-terminal parts. The B-chain C-terminal part of bombyxin-II adopts an extension of the B-chain central helix like that of relaxin and is not required for bombyxin activity, while the corresponding part of insulin adopts a sharp turn and a beta-strand and is essential for insulin activity. This structure demonstrates that bombyxin-II is more closely related to relaxin than to insulin, and suggests that insulin might have evolved the additional receptor-recognition site in the B-chain C-terminal beta-strand to distinguish itself from bombyxin and relaxin. The structure of bombyxin-II thus provides novel insights into the receptor recognition and divergent molecular evolution of insulin-superfamily peptides.

Amino Acid Sequence↗