Arndt von Haeseler

Unexpected complexity of the Wnt gene family in a sea anemone

The Wnt gene family encodes secreted signalling molecules that control cell fate in animal development and human diseases. Despite its significance, the evolution of this metazoan-specific protein family is unclear. In vertebrates, twelve Wnt subfamilies were defined, of which only six have counterparts in Ecdysozoa (for example, Drosophila and Caenorhabditis). Here, we report the isolation of twelve Wnt genes from the sea anemone Nematostella vectensis , a species representing the basal group within cnidarians. Cnidarians are diploblastic animals and the sister-group to bilaterian metazoans. Phylogenetic analyses of N. vectensis Wnt genes reveal a thus far unpredicted ancestral diversity within the Wnt family. Cnidarians and bilaterians have at least eleven of the twelve known Wnt gene subfamilies in common; five subfamilies appear to be lost in the protostome lineage. Expression patterns of Wnt genes during N. vectensis embryogenesis indicate distinct roles of Wnts in gastrulation, resulting in serial overlapping expression domains along the primary axis of the planula larva. This unexpectedly complex inventory of Wnt family signalling factors evolved in early multi-cellular animals about 650u2009million years (Myr) ago, predating the Cambrian explosion by at least 100u2009Myr (refs 5, 8). It emphasizes the crucial function of Wnt genes in the diversification of eumetazoan body plans.

Haplotype structure at seven barley genes: relevance to gene pool bottlenecks, phylogeny of ear type and site of barley domestication

Archaeological remains indicate that the origin of western agriculture occurred in a brief period about 10,500xa0years ago in a region of the Middle East known as the Fertile Crescent, where the wild progenitors of several key agricultural cereal species are endemic. Domestication entailed the appearance of agronomic traits such as seed size and threshability. For a representative sample of 20 domesticated barley (Hordeum vulgare) lines, including 13 two-rowed and 7 six-rowed varieties, we determined the haplotypes at seven loci—Adh2, Adh3, Amy1, Dhn9, GAPDH, PEPC and WAXY encompassing 5,616 bases per line—and compared them to the haplotypes at the same loci for 25 wild forms (Hordeum spontaneum) collected within and outside the Fertile Crescent. In comparisons of wild versus domesticated barley, the number of haplotypes (70 vs. 17), average nucleotide diversity, π, (0.0077 vs. 0.0028), and Watterson’s theta at silent sites (0.0104 vs. 0.0028) was reduced in domesticated lines. Two loci, Amy1 and PEPC, were monomorphic in domesticated lines; Amy1 and GAPDH produced significant values of Tajima’s D. At GAPDH, π was slightly higher in domesticated than wild forms, due to divergent high-frequency haplotypes; for the remaining six loci, 87% of nucleotide diversity has been lost in the domesticated forms. Bottlenecks acting on neutrally evolving loci either during the domestication process, during subsequent breeding, or both, are sufficient to account for reduced diversity and the results of Tajima’s test, without the need to evoke selection at these loci. Phylogenetic networks data uncover distinct wild and domesticated barley genotypes and suggest that barley may have been domesticated in the Jordan valley. Because, based on AFLP data, the domesticated Turkish cultivars had a genetic basis as large as that present in large germplasm collections, all comparisons provided in this paper are of general value more than being restricted to the Turkish barley germplasm.

Simultaneous Statistical Multiple Alignment and Phylogeny Reconstruction

Although the reconstruction of phylogenetic trees and the computation of multiple sequence alignments are highly interdependent, these two areas of research lead quite separate lives, the former often making use of stochastic modeling, whereas the latter normally does not. Despite the fact that reasonable insertion and deletion models for sequence pairs were already introduced more than 10 years ago, they have only recently been applied to multiple alignment and only in their simplest version. In this paper we present and discuss a strategy based on simulated annealing, which makes use of these models to infer a phylogenetic tree for a set of DNA or protein sequences together with the sequencesindel history, i.e., their multiple alignment augmented with information about the positioning of insertion and deletion events in the tree. Our method is also the first application of the TKF2 model in the context of multiple sequence alignment. We validate the method via simulations and illustrate it using a data set of primate mtDNA.

Conserved pore-forming regions in polypeptide-transporting proteins

Transport of solutes and polypeptides across membranes is an essential process for every cell. In the past, much focus has been placed on helical transporters. Recently, the β‐barrel‐shaped transporters have also attracted some attention. The members of this family are found in the outer bacterial membrane and the outer membrane of endosymbiotically derived organelles. Here we analyze the features and the evolutionary development of a specified translocator family, namely the β‐barrel‐shaped polypeptide‐transporters. We identified sequence motifs, which characterize all transporters of this family, as well as motifs specific for a certain subgroup of proteins of this class. The general motifs are related to the structural composition of the pores. Further analysis revealed a defined distance of two motifs to the C‐terminal portion of the proteins. Furthermore, the evolutionary relationship of the proteins and the motifs are discussed.

Shortest triplet clustering: reconstructing large phylogenies using representative sets

Understanding the evolutionary relationships among species based on their genetic information is one of the primary objectives in phylogenetic analysis. Reconstructing phylogenies for large data sets is still a challenging task in Bioinformatics. We propose a new distance-based clustering method, the shortest triplet clustering algorithm (STC), to reconstruct phylogenies. The main idea is the introduction of a natural definition of so-called k-representative sets. Based on k-representative sets, shortest triplets are reconstructed and serve as building blocks for the STC algorithm to agglomerate sequences for tree reconstruction in O(n2) time for n sequences. Simulations show that STC gives better topological accuracy than other tested methods that also build a first starting tree. STC appears as a very good method to start the tree reconstruction. However, all tested methods give similar results if balanced nearest neighbor interchange (BNNI) is applied as a post-processing step. BNNI leads to an improvement in all instances. The program is available at http://www.bi.uni-duesseldorf.de/software/stc/ . The results demonstrate that the new approach efficiently reconstructs phylogenies for large data sets. We found that BNNI boosts the topological accuracy of all methods including STC, therefore, one should use BNNI as a post-processing step to get better topological accuracy.

The Phylogenetic Handbook: Genetic distances and nucleotide substitution models

One of the first steps in the analysis of aligned nucleotide or amino acid sequences typically is the computation of the matrix of genetic distances (or evolutionary distances) between all pairs of sequences. In the present chapter we discuss two questions that arise in this context. First, what is a reasonable definition of a genetic distance, and second, how to estimate it using statistical models of the substitution process. It is well known that a variety of evolutionary forces act on DNA sequences (see Chapter 1). As a result, sequences change in the course of time. Therefore, any two sequences derived from a common ancestor that evolve independently of each other eventually diverge (see Fig. 4.1). A measure of this divergence is called a genetic distance. Not surprisingly, this quantity plays an important role in many aspects of sequence analysis. First, by definition it provides a measure of the similarity between sequences. Second, if a molecular clock is assumed (see Chapter 11), then the genetic distance is linearly proportional to the time elapsed. Third, for sequences related by an evolutionary tree, the branch lengths represent the distance between the nodes (sequences) in the tree. Therefore, if the exact amount of sequence divergence between all pairs of sequences from a set of n sequences is known, the genetic distance provides a basis to infer the evolutionary tree relating the sequences. In particular, if sequences actually evolved according to a tree and if

Retraction Note: TREEFINDER: a powerful graphical analysis environment for molecular phylogenetics

Most analysis programs for inferring molecular phylogenies are difficult to use, in particular for researchers with little programming experience. TREEFINDER is an easy-to-use integrative platform-independent analysis environment for molecular phylogenetics. In this paper the main features of TREEFINDER (version of April 2004) are described. TREEFINDER is written in ANSI C and Java and implements powerful statistical approaches for inferring gene tree and related analyzes. In addition, it provides a user-friendly graphical interface and a phylogenetic programming language. TREEFINDER is a versatile framework for analyzing phylogenetic data across different platforms that is suited both for exploratory as well as advanced studies.

PhyNav: A Novel Approach to Reconstruct Large Phylogenies

A novel method, PhyNav, is introduced to reconstruct the evolutionary relationship among contemporary species based on their genetic data. The key idea is the definition of the so-called minimal κ-distance subset which contains most of the relevant phylogenetic information from the whole dataset. For this reduced subset the subtree is created faster and serves as a scaffold to construct the full tree. Because many minimal subsets exist the procedure is repeated several times and the best tree with respect to some optimality criterion is considered as the inferred phylogenetic tree. PhyNav gives encouraging results compared to other programs on both simulated and real datasets.

Stochastic Insertion-Deletion Processes and Statistical Sequence Alignment

The reconstruction of the history of a set of sequences is a central problem in molecular evolutionary biology. Typically this history is summarized in a phylogenetic tree. In current practice the estimation of a phylogenetic tree is a two-step procedure: first a multiple alignment is computed and subsequently a phylogenetic tree is reconstructed, based on the alignment. However, it is well known that the alignment and the tree reconstruction problem are intertwined. Thus, it is of great interest to estimate alignment and tree simultaneously. We present here a stochastic framework for this joint estimation. We discuss a variant of the Thorne-Kishino-Felsenstein model, having equal rates of insertions and of deletions of sequence fragments, for (ell ) ≥ 2 sequences related by a phylogenetic tree. Finally, we review novel approaches to tree reconstruction based on insertion-deletion models.