ECB-ART-46926
BMC Evol Biol
2019 Jan 31;191:40. doi: 10.1186/s12862-019-1360-0.
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Taxon-specific expansion and loss of tektins inform metazoan ciliary diversity.
Bastin BR
,
Schneider SQ
.
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BACKGROUND: Cilia and flagella are complex cellular structures thought to have first evolved in a last ciliated eukaryotic ancestor due to the conserved 9 + 2 microtubule doublet structure of the axoneme and associated proteins. The Tektin family of coiled-coil domain containing proteins was previously identified in cilia of organisms as diverse as green algae and sea urchin. While studies have shown that some Tektins are necessary for ciliary function, there has been no comprehensive phylogenetic survey of tektin genes. To fill this gap, we sampled tektin sequences broadly among metazoan and unicellular lineages in order to determine how the tektin gene complements evolved in over 100 different extant species. RESULTS: Using Bayesian and Maximum Likelihood analyses, we have ascertained with high confidence that all metazoan tektins arose from a single ancestral tektin gene in the last common ancestor of metazoans and choanoflagellates. Gene duplications gave rise to two tektin genes in the metazoan ancestor, and a subsequent expansion to three and four tektin genes in early bilaterian ancestors. While all four tektin genes remained highly conserved in most deuterostome and spiralian species surveyed, most tektin genes in ecdysozoans are highly derived with extensive gene loss in several lineages including nematodes and some crustaceans. In addition, while tektin-1, - 2, and - 4 have remained as single copy genes in most lineages, tektin-3/5 has been duplicated independently several times, notably at the base of the spiralian, vertebrate and hymenopteran (Ecdysozoa) clades. CONCLUSIONS: We provide a solid description of tektin evolution supporting one, two, three, and four ancestral tektin genes in a holozoan, metazoan, bilaterian, and nephrozoan ancestor, respectively. The isolated presence of tektin in a cryptophyte and a chlorophyte branch invokes events of horizontal gene transfer, and that the last common ciliated eukaryotic ancestor lacked a tektin gene. Reconstructing the evolutionary history of the tektin complement in each extant metazoan species enabled us to pinpoint lineage specific expansions and losses. Our analysis will help to direct future studies on Tektin function, and how gain and loss of tektin genes might have contributed to the evolution of various types of cilia and flagella.
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Species referenced: Echinodermata
Genes referenced: cep89 dnah3 irak1bp1 LOC100887844 LOC100893907 LOC115925415 LOC576114 LOC576378 tekt1 tekt3 tubgcp2
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Fig. 1. Structure and Localization of Tektins. a Schematic of the general structure of Tektin proteins consisting of two N-terminal alpha-helices (Helix 1A and Helix 1B) and a pair of C-terminal alpha-helices (Helix 2A and Helix 2B), separated by linker regions. Conserved amino acid motifs identified by Amos [20] are shown above. Conserved amino acid motifs identified in this study indicate similar motifs in the linker regions between the A and B helices of both alpha-helix pairs (black letters) as well as at the C-terminus of both B helices (red letters) are shown below. b Phylogenetic tree of metazoans and choanoflagellates indicating the evolutionary positions of the major phyla and key species examined in this study. c Location and composition of Tektin filaments within the axoneme of a motile cilium as proposed by Linck et al. [24]. The lower scheme shows a transverse section of the axoneme with the typical 9 plus 2 arrangements of 9 pairs of complete and incomplete microtubules (A in red, and B in blue, respectively) surrounding a central pair of A microtubules. Outer (yellow) and inner (red) dynein motor complexes, as well as radial spokes (blue) originating from each A microtubule are shown. The upper scheme details one doublet microtubule showing the thirteen and ten tubulin protofilaments that constitute the A- and B-microtubule, respectively, and the proposed localization of the Tektin filament (green sphere). Tektin filaments are thought to run along the inside of the A microtubule in each microtubule doublet of the axoneme. Tektin filaments are thought to be composed of multiples of three protein dimers: two Tektin-A/Tektin-B (Tektin-4/Tektin-2) heterodimers (thin red A and blue B circles) and one Tektin-C (Tektin-1) homodimer (thin green C circles) |
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Fig. 2. Alignment and conserved motifs of Tektin proteins. Amino acid alignment of conserved regions of the Tektin protein complements from D. melanogaster (Dm), H. sapiens (Hs) and P. dumerilii (Pd) are shown grouped by the four Tektin classes: Tektin-1 or C, Tektin-2, Tektin 3/5, and Tektin-4 or A. The Tektin-3/5 class includes two human (3 and 5) and two Platynereis (3/5A and 3/5B) Tektins. Two pairs of alpha helices (Helix 1 and 2) are highlighted by pink boxes (compare to Fig. 1a). Conserved residues are color-coded using Aliview. The highly conserved nonapeptide motif between Helix 2A and Helix 2B [20] is highlighted above the alignment. Motifs identified in this study are highlighted below the alignment, and include a highly conserved motif (L . . R . . R . . . D/E L . . D) within the short regions between Helix 1A and 1B and Helix 2A and 2B, and a second conserved motif (L E . D . . . K . . . . . I D . . (.) C) within the C-terminus of Helix 1B and Helix 2B |
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Fig. 3. Phylogenetic tree to illustrate the evolution of the Tektin complement in metazoan species. This phylogenetic analysis includes the full Tektin complements identified in selected metazoan species including four xenacoelamorphans (Cma, Ipu, Mst, Xbo), six ecdysozoans (Ae, Ame, Bt, Dm, Tc, Zn), four spiralian species (Cg, Ct, La, Pd), three invertebrate deuterostomes (Sk, Sp, Bf), and six vertebrate deuterostomes (Ap, Cpb, Gg, Mm, Oa, Hs), as well as two nonbilaterians (Aq, Nv), one choanoflagellate (Sr) and a green algae (Chr) as an outgroup. Both Bayesian and Maximum Likelihood analyses were performed using Mr. Bayes and RAxML, respectively. The Bayesian tree topology is shown. Node support is shown for non-terminal nodes. Posterior probability values from Mr. Bayes and bootstrap values from RAxML are shown above or below each node, respectively. Diamonds indicate support less than 80%. âXâ under a node indicates that this node was not recovered in the RAxML maximum likelihood tree. Tree was rooted with green algae (Chr) Tektin. The large colored boxes highlight the four major Tektin classes that exist in bilaterians, Tektin-2 (green), Tektin-4 (light blue), Tektin-1 (yellow), and Tektin-3/5 (purple), the nonbilaterian class Tektin-1/4/3/5 (orange) and the ancestral non-metazoan Tektin-2/1/4/3/5 (pink). The smaller colored boxes within the Tektin-3/5 class group Tektins that belong to higher taxa as indicated to highlight the three independent duplications of Tektin-3/5 at the base of the ecdysozoan hymenopterans (Tektin-3/5a andâââ3/5b), the spiralians (Tektin-3/5A and 3/5B), and the deuterostome vertebrates (Tektin-3 and Tektin-5). All metazoans share Tektin-2 while the nonbilaterian Tektin-1/4/3/5 is sister group to the three exclusively bilaterian Tektin classes Tektin-1, Tektin-4, and Tektin-3/5. Tektins are named according to the groups recovered by this phylogenetic analysis. Species abbreviations and accession numbers for each sequence are provided in Additional file 5 |
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Fig. 4. Phylogenetic tree to illustrate the evolution of the Tektin complement in nonbilaterian species. This phylogenetic analysis includes the full Tektin complements identified in six cnidarians (Aa, Che, Hv, Ad, Ep, Nv), three ctenophores (Ba, Pb, Ml), six poriferans (Oc, Em, Ha, Aq, Ht, Sc), and four bilaterians (Tc, Pd, Hs, Sk), as well as two choanoflagellates (Sr and Mo) as outgroups. Both Bayesian and Maximum Likelihood analyses were performed using Mr. Bayes and RAxML, respectively. The Bayesian tree topology is shown. Node support is shown for non-terminal nodes. Posterior probability values from Mr. Bayes and bootstrap values from RAxML are shown above or below each node, respectively. Diamonds indicate support less than 80%. âXâ under a node indicates that this node was not recovered in the RAxML maximum likelihood tree. Tree was rooted with choanoflagellate sequences. Nonbilaterian Tektins fall into one of two groups: Tektin-2 and Tektin-1/4/3/5. Tektins are named according to the groups recovered by this phylogenetic analysis. Species abbreviations and accession numbers for each sequence are provided in Additional file 5 |
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Fig. 5. Phylogenetic tree to illustrate the evolution of Tektin-2 in bilaterian species. This phylogenetic analysis includes the Tektin-2 sequences identified in bilaterian species. The 23 spiralians include six mollusks (Ac, Bg, Ob, Lg, Cg, Pf), twelve platyhelminthes (Cs, Ov, Sch, Scm, Scj, Eg, Emu, Taa, Tas. Hmi, Sme, and Mli), three annelids (Pd, Ct, Hr), one brachiopod (La), and one orthonectid (Il). The ecdysozoans include many insects, two chelicerates (Pt, Smi), one myriapod (Sma), one tardigrade (Hd), and one priapulid (Pc). The invertebrate deuterostomes are represented by one echinoderm (Sp), one hemichordate (Sk), one cephalochordate (Bf), and one urochordate (Ci). The vertebrate deuterostomes are represented by three teleost fishes (Dr, Tr, and Ch), one holostei fish (Lo), one chondrichthyes (Cm), one sarcopterygian fish (Lc), three amphibians (Xl, Amb, Nvi), one reptile (Cpb), two avians (Ap, Gg), and three mammal species (Oa, Mm, Hs). In addition, the entire Tektin complement for an annelid (Pd) and human (Hs) was included as well as two choanoflagellate (Sr, Mo) sequences as outgroups. Both Bayesian and Maximum Likelihood analyses were performed using Mr. Bayes and RAxML, respectively. The Bayesian tree topology is shown. Node support is shown for non-terminal nodes. Posterior probability values from Mr. Bayes and bootstrap values from RAxML are shown above or below each node, respectively. Diamonds indicate support less than 80%. âXâ under a node indicates that this node was not recovered in the RAxML maximum likelihood tree. The large colored boxes group Tektin-2 sequences of the three major bilaterian branches, the spiralians (green), the ecdysozoans (blue), and the deuterostomes (orange). The smaller colored boxes within ecdysozoans and spiralians highlight Tektin-2 gene duplications at the base of insect lepidopterans (light purple), and one duplication in the Platyhelminthes lineage including the planarian (Sme) and the parasitic trematodes and cestodes, but excluding the flatworm (Mli) (dark green), respectively. Note that tektin-2 exists as a single copy gene in most extant species with only two additional duplicates observed in the leech (Hr) and louse (Phc). Species abbreviations and accession numbers for each sequence are provided in Additional file 5 |
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Fig. 6. Phylogenetic tree to illustrate the evolution of Tektin-1 in bilaterian species. This phylogenetic analysis includes the Tektin-1 sequences identified in bilaterian species. The 23 spiralians include six mollusks (Ac, Bg, Ob, Lg, Cg, Pf), 12 platyhelminthes (Cs, Ov, Sch, Scm, Scj, Eg, Emu, Taa, Tas. Hmi, Sme, and Mli), three annelids (Pd, Ct, Hr), and one brachiopod (La). The ecdysozoans include many insects, two chelicerates (Pt, Smi), one myriapod (Sma), one crustacean (Dp), one dicyemid (Dj), one tardigrade (Hd), and one priapulid (Pc). The invertebrate deuterostomes are represented by one echinoderm (Sp), one hemichordate (Sk), one cephalochordate (Bf), and one urochordate (Ci). The vertebrate deuterostomes are represented by three teleost fish (Dr, Tr, and Ch), one holostei fish (Lo), one chondrichthyes (Cm), one sarcopterygian fish (Lc), three amphibian (Xl, Amb, Nvi), one reptile (Cpb) two avians (Ap, Gg), and three mammal species (Oa, Mm, Hs). In addition, Tektin-4 sequences from C. gigas, P. dumerilii, S. kowalevskii, D. rerio and H. sapiens were included as an outgroup. The tree was rooted with N. vectensis Tektin-1/4/3/5A. Both Bayesian and Maximum Likelihood analyses were performed using Mr. Bayes and RAxML, respectively. The Bayesian tree topology is shown. Node support is shown for non-terminal nodes. Posterior probability values from Mr. Bayes and bootstrap values from RAxML are shown above or below each node, respectively. Diamonds indicate support less than 80%. âXâ under a node indicates that this node was not recovered in the RAxML maximum likelihood tree. The large colored boxes group Tektin-1 sequences of the three major bilaterian branches, the spiralians (green), the ecdysozoans (blue), and the deuterostomes (orange). Note that tektin-1 exists as a single copy gene in most extant species with only two duplicate tektin-1 genes observed in two spiralian species, a leech (Hr) and a planarian (Sme). Species abbreviations and accession numbers for each sequence are provided in Additional file 5 |
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Fig. 7. Phylogenetic tree to illustrate the evolution of Tektin-4 in bilaterian species. This phylogenetic analysis includes the Tektin-4 sequences identified in bilaterian species. The 23 spiralians include six mollusks (Ac, Bg, Ob, Lg, Cg, Pf), 12 platyhelminthes (Cs, Ov, Sch, Scm, Scj, Eg, Emu, Taa, Tas, Hmi, Sme, and Mli), three annelids (Pd, Ct, Hr), and one brachiopod (La). The ecdysozoans include many insects, two chelicerates (Pt, Smi), one myriapod (Sma), and one priapulid (Pc). The invertebrate deuterostomes are represented by one echinoderm (Sp), one hemichordate (Sk), one cephalochordate (Bf), and one urochordate (Ci). The vertebrate deuterostomes are represented by three teleost fish (Dr, Tr, and Ch), one holostei fish (Lo), one chondrichthyes (Cm), one sarcopterygian fish (Lc), three amphibian (Xl, Amb, Nvi), one reptile (Cpb) two avians (Ap, Gg), and three mammal species (Oa, Mm, Hs). In addition, Tektin-3/5 sequences from B. floridae, S. kowalevskii, S. purpuratus, D. melanogaster and T. castaneum were included as an outgroup. The tree was rooted with N. vectensis Tektin-1/4/3/5A. Both Bayesian and Maximum Likelihood analyses were performed using Mr. Bayes and RAxML, respectively. The Bayesian tree topology is shown. Node support is shown for non-terminal nodes. Posterior probability values from Mr. Bayes and bootstrap values from RAxML are shown above or below each node, respectively. Diamonds indicate support less than 80%. âXâ under a node indicates that this node was not recovered in the RAxML maximum likelihood tree. The large colored boxes group Tektin-4 sequences of the three major bilaterian branches, the spiralians (green), the ecdysozoans (blue), and the deuterostomes (orange). The smaller colored boxes within ecdysozoans and spiralians highlight two gene duplications of tektin-4 at the base of insect lepidopterans (purple), and one duplication in the Platyhelminthes lineage including the planarian Sm and the parasitic trematodes and cestodes, but excluding the flatworm Mli (dark green), respectively. Note that only two platyhelminthes species retained both Tektin-4a and -4b (Sme and Cs), while others lost one of the duplicates (Eg, Emu, Ov, Taa, Tas, Hmi, Sch, Scm, Scj). Note that tektin-4 exists as a single copy gene in most extant species with only one additional duplicated Tektin-4 gene observed in the spiralian leech (Hr). Species abbreviations and accession numbers for each sequence are provided in Additional file 5 |
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Fig. 8. Phylogenetic tree to illustrate the evolution of Tektin-3/5 in bilaterian species. This phylogenetic analysis includes the Tektin-3/5 sequences identified in bilaterian species. The nine spiralians include five mollusks (Ac, Bg, Lg, Cg, Pf), one platyhelminthes (Mli), two annelids (Pd, Ct), and one brachiopod (La). The 17 ecdysozoans include many insects, one myriapod (Sma), and one priapulid (Pc). The invertebrate deuterostomes are represented by one echinoderm (Sp), one hemichordate (Sk), one cephalochordate (Bf), and one urochordate (Ci). The vertebrate deuterostomes are represented by eight teleost fish (Am, El, Sf, Ss, On, Dr., Tr, and Ch), one holostei fish (Lo), one chondrichthyes (Cm), one sarcopterygian fish (Lc), three amphibians (Xl, Amb, Nvi), one reptile (Cpb), two avians (Ap, Gg), and three mammal species (Oa, Mm, Hs). In addition, Tektin-4 sequences from C. gigas, P. dumerilii, S. kowalevskii, D. rerio and H. sapiens were included as an outgroup. The tree was rooted with N. vectensis Tektin-1/4/3/5A. Both Bayesian and Maximum Likelihood analyses were performed using Mr. Bayes and RAxML, respectively. The Bayesian tree topology is shown. Node support is shown for non-terminal nodes. Posterior probability values from Mr. Bayes and bootstrap values from RAxML are shown above or below each node, respectively. Diamonds indicate support less than 80%. âXâ under a node indicates that this node was not recovered in the RAxML maximum likelihood tree. The large colored boxes group Tektin-3/5 sequences of major bilaterian branches, the spiralians (light blue), the ecdysozoans (purple), the invertebrate deuterostomes (pink), and the deuterostome vertebrates (orange). The smaller colored boxes within spiralians, ecdysozoans and vertebrates highlight three independent gene duplications of the tektin-3/5 gene at the base of spiralians giving rise to Tektin-3/5A (dark green) and tektin-3/5B (light green), at the base of insect hymenopterans giving rise to Tektin-3/5a andâââ3/5b (dark pink), and at the base of vertebrates giving rise to Tektin-3 (dark purple) and Tektin-5 (light grey), respectively. Note that most teleost fish species (dark grey), and two of the three amphibian species (Nvi and Xl) retained Tektin-3 but lost Tektin-5. Note that the tektin-3/5 gene exists as a single copy gene in most ecdysozoans and the four invertebrate deuterostomes (Sp, Sk, Bf, Ci). Species abbreviations and accession numbers for each sequence are provided in Additional file 5 |
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Fig. 9. Overview of metazoan tektin gene family evolution. a Evidence-based parsimonious hypothesis of the evolution of the tektin gene family in metazoans. Results from this study are displayed within a mostly accepted phylogeny of metazoan taxa. The branching pattern of nonbilaterian taxa especially the ctenophores are still debated. However, the proposed scenario is consistent with either ctenophores or poriferans as the earliest branching metazoan taxon. The number of hypothesized ancestral tektin genes is given at each major node (blue circles) with a suggested nomenclature that reflects the evolutionary origin on the Tektin classes is given at the right margin. Note that according to our analysis the four Tektin classes, Tektin-1, ââ2, ââ4, and 3/5 exist only in bilaterians, while the extant bilaterian and nonbilaterian tektin gene complements originated from two ancestral metazoan tektins, tektin-2 and tektin-1/4/3/5. Major duplications (blue squares) and losses (blue crosses) of tektin genes that affect every species within a phylum are shown. Metazoan phyla and in parenthesis the range of tektin genes found within species of each phylum are shown in the top row. Number of tektin genes range from complete absence in placozoans (0) by gene loss, to ten tektin genes in the annelid leech (10) by multiple gene duplications. Note that three spiralian taxa, the platyhelminthes (5â10), the annelids (5â10), and the mollusks (5â8) contain each species with the ancestral spiralian tektin gene complement of five, and species that have expanded their complement up to ten tektin genes by independent gene duplications. Uncertainty of the placement of the Xenacoelomorpha either before or after the duplication of tektin-4/3/5 leading to tektin-4 and tektin-3/5 is indicated by dotted lines. b Hypothesized scenario for the evolution of the Tektin filament. Pioneering biochemical and structural studies on tektins in motile cilia of sea urchins by Linck and colleagues have provided evidence for axonemal Tektin filaments constructed by multiples of two heterodimers built with Tektin-2 (green circle) and Tektin-4 (red circle), and one homodimer built with Tektin-1 (blue circle) protein units (compare to Fig. 1c). This phylogenetic study provided evidence that these three Tektins existed already in a bilaterian ancestor including a fourth Tektin-3/5 (yellow circle) with unknown filamentous Tektin functions (shown in right column), and enables predictions about the composition for earlier stages in Tektin filament evolution with the ancestral tektin gene complements comprising of one (tektin-2/1/4/3/5, black circle), two (tektin-2, green circle; tektin-1/4/3/5, purple circle), and three tektin genes in the unicellular, metazoan, and early bilaterian ancestor, respectively (shown in three left columns). Upper row shows which predicted Tektin protein makes up the filamentous Tektin units at discreet steps in metazoan evolution, and lists extant organisms in which this prediction could be tested. Lower row shows diagrams of the predicted composition of the hypothetical Tektin filament at discreet steps in evolution |
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