Publications by authors named "Michael Volkmer"

7 Publications

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HH-MOTiF: de novo detection of short linear motifs in proteins by Hidden Markov Model comparisons.

Nucleic Acids Res 2017 10;45(18):10921

Computational Biology Group, Max Planck Institute of Biochemistry, Martinsried, Germany.

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http://dx.doi.org/10.1093/nar/gkx810DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5737479PMC
October 2017

HH-MOTiF: de novo detection of short linear motifs in proteins by Hidden Markov Model comparisons.

Nucleic Acids Res 2017 07;45(W1):W470-W477

Computational Biology Group, Max Planck Institute of Biochemistry, Martinsried, Germany.

Short linear motifs (SLiMs) in proteins are self-sufficient functional sequences that specify interaction sites for other molecules and thus mediate a multitude of functions. Computational, as well as experimental biological research would significantly benefit, if SLiMs in proteins could be correctly predicted de novo with high sensitivity. However, de novo SLiM prediction is a difficult computational task. When considering recall and precision, the performances of published methods indicate remaining challenges in SLiM discovery. We have developed HH-MOTiF, a web-based method for SLiM discovery in sets of mainly unrelated proteins. HH-MOTiF makes use of evolutionary information by creating Hidden Markov Models (HMMs) for each input sequence and its closely related orthologs. HMMs are compared against each other to retrieve short stretches of homology that represent potential SLiMs. These are transformed to hierarchical structures, which we refer to as motif trees, for further processing and evaluation. Our approach allows us to identify degenerate SLiMs, while still maintaining a reasonably high precision. When considering a balanced measure for recall and precision, HH-MOTiF performs better on test data compared to other SLiM discovery methods. HH-MOTiF is freely available as a web-server at http://hh-motif.biochem.mpg.de.
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http://dx.doi.org/10.1093/nar/gkx341DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5570144PMC
July 2017

morFeus: a web-based program to detect remotely conserved orthologs using symmetrical best hits and orthology network scoring.

BMC Bioinformatics 2014 Aug 6;15:263. Epub 2014 Aug 6.

Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried 82152, Germany.

Background: Searching the orthologs of a given protein or DNA sequence is one of the most important and most commonly used Bioinformatics methods in Biology. Programs like BLAST or the orthology search engine Inparanoid can be used to find orthologs when the similarity between two sequences is sufficiently high. They however fail when the level of conservation is low. The detection of remotely conserved proteins oftentimes involves sophisticated manual intervention that is difficult to automate.

Results: Here, we introduce morFeus, a search program to find remotely conserved orthologs. Based on relaxed sequence similarity searches, morFeus selects sequences based on the similarity of their alignments to the query, tests for orthology by iterative reciprocal BLAST searches and calculates a network score for the resulting network of orthologs that is a measure of orthology independent of the E-value. Detecting remotely conserved orthologs of a protein using morFeus thus requires no manual intervention. We demonstrate the performance of morFeus by comparing it to state-of-the-art orthology resources and methods. We provide an example of remotely conserved orthologs, which were experimentally shown to be functionally equivalent in the respective organisms and therefore meet the criteria of the orthology-function conjecture.

Conclusions: Based on our results, we conclude that morFeus is a powerful and specific search method for detecting remotely conserved orthologs. morFeus is freely available at http://bio.biochem.mpg.de/morfeus/. Its source code is available from Sourceforge.net (https://sourceforge.net/p/morfeus/).
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http://dx.doi.org/10.1186/1471-2105-15-263DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4137093PMC
August 2014

Comparative transcriptional profiling of the axolotl limb identifies a tripartite regeneration-specific gene program.

PLoS One 2013 1;8(5):e61352. Epub 2013 May 1.

Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.

Understanding how the limb blastema is established after the initial wound healing response is an important aspect of regeneration research. Here we performed parallel expression profile time courses of healing lateral wounds versus amputated limbs in axolotl. This comparison between wound healing and regeneration allowed us to identify amputation-specific genes. By clustering the expression profiles of these samples, we could detect three distinguishable phases of gene expression - early wound healing followed by a transition-phase leading to establishment of the limb development program, which correspond to the three phases of limb regeneration that had been defined by morphological criteria. By focusing on the transition-phase, we identified 93 strictly amputation-associated genes many of which are implicated in oxidative-stress response, chromatin modification, epithelial development or limb development. We further classified the genes based on whether they were or were not significantly expressed in the developing limb bud. The specific localization of 53 selected candidates within the blastema was investigated by in situ hybridization. In summary, we identified a set of genes that are expressed specifically during regeneration and are therefore, likely candidates for the regulation of blastema formation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0061352PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3641036PMC
February 2014

Comparative RNA-seq analysis in the unsequenced axolotl: the oncogene burst highlights early gene expression in the blastema.

PLoS Comput Biol 2013 7;9(3):e1002936. Epub 2013 Mar 7.

Regenerative Biology, Morgridge Institute for Research, Madison, Wisconsin, United States of America.

The salamander has the remarkable ability to regenerate its limb after amputation. Cells at the site of amputation form a blastema and then proliferate and differentiate to regrow the limb. To better understand this process, we performed deep RNA sequencing of the blastema over a time course in the axolotl, a species whose genome has not been sequenced. Using a novel comparative approach to analyzing RNA-seq data, we characterized the transcriptional dynamics of the regenerating axolotl limb with respect to the human gene set. This approach involved de novo assembly of axolotl transcripts, RNA-seq transcript quantification without a reference genome, and transformation of abundances from axolotl contigs to human genes. We found a prominent burst in oncogene expression during the first day and blastemal/limb bud genes peaking at 7 to 14 days. In addition, we found that limb patterning genes, SALL genes, and genes involved in angiogenesis, wound healing, defense/immunity, and bone development are enriched during blastema formation and development. Finally, we identified a category of genes with no prior literature support for limb regeneration that are candidates for further evaluation based on their expression pattern during the regenerative process.
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http://dx.doi.org/10.1371/journal.pcbi.1002936DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3591270PMC
November 2013

Caenorhabditis elegans screen reveals role of PAR-5 in RAB-11-recycling endosome positioning and apicobasal cell polarity.

Nat Cell Biol 2012 May 27;14(7):666-76. Epub 2012 May 27.

Max Planck Institute of Molecular Cell Biology and Genetics, MPI-CBG, Pfotenhauerstrasse 108, 01307 Dresden, Germany.

Apically enriched Rab11-positive recycling endosomes (Rab11-REs) are important for establishing and maintaining epithelial polarity. Yet, little is known about the molecules controlling trafficking of Rab11-REs in an epithelium in vivo. Here, we report a genome-wide, image-based RNA interference screen for regulators of Rab11-RE positioning and transport of an apical membrane protein (PEPT-1) in C. elegans intestine. Among the 356 screen hits was the 14-3-3 and partitioning defective protein PAR-5, which we found to be specifically required for Rab11-RE positioning and apicobasal polarity maintenance. Depletion of PAR-5 induced abnormal clustering of Rab11-REs to ectopic sites at the basolateral cortex containing F-actin and other apical domain components. This phenotype required key regulators of F-actin dynamics and polarity, such as Rho GTPases (RHO-1 and the Rac1 orthologue CED-10) and apical PAR proteins. Our data suggest that PAR-5 acts as a regulatory hub for a polarity-maintaining network required for apicobasal asymmetry of F-actin and proper Rab11-RE positioning.
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http://dx.doi.org/10.1038/ncb2508DOI Listing
May 2012

An Ambystoma mexicanum EST sequencing project: analysis of 17,352 expressed sequence tags from embryonic and regenerating blastema cDNA libraries.

Genome Biol 2004 13;5(9):R67. Epub 2004 Aug 13.

Scionics Computer Innovation GmbH, Pfotenhauerstrasse 110, Dresden 01307, Germany.

Background: The ambystomatid salamander, Ambystoma mexicanum (axolotl), is an important model organism in evolutionary and regeneration research but relatively little sequence information has so far been available. This is a major limitation for molecular studies on caudate development, regeneration and evolution. To address this lack of sequence information we have generated an expressed sequence tag (EST) database for A. mexicanum.

Results: Two cDNA libraries, one made from stage 18-22 embryos and the other from day-6 regenerating tail blastemas, generated 17,352 sequences. From the sequenced ESTs, 6,377 contigs were assembled that probably represent 25% of the expressed genes in this organism. Sequence comparison revealed significant homology to entries in the NCBI non-redundant database. Further examination of this gene set revealed the presence of genes involved in important cell and developmental processes, including cell proliferation, cell differentiation and cell-cell communication. On the basis of these data, we have performed phylogenetic analysis of key cell-cycle regulators. Interestingly, while cell-cycle proteins such as the cyclin B family display expected evolutionary relationships, the cyclin-dependent kinase inhibitor 1 gene family shows an unusual evolutionary behavior among the amphibians.

Conclusions: Our analysis reveals the importance of a comprehensive sequence set from a representative of the Caudata and illustrates that the EST sequence database is a rich source of molecular, developmental and regeneration studies. To aid in data mining, the ESTs have been organized into an easily searchable database that is freely available online.
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http://dx.doi.org/10.1186/gb-2004-5-9-r67DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC522874PMC
May 2005