Biology subjects

Kollmar, M.

Publications and source records attributed to Kollmar, M..

6 recordsLinked to original sources

bioRxiv2024

Cryptic Variation in Adaptive Phenotypes Revealed by Panspecific flc Mutants

The study of mutants is one of the best tools for understanding the genetic basis of phenotypes that contribute to adaptation. Oddly, mutant analyses are almost always restricted to single genetic backgrounds and findings therefore can not be easily generalized. A case in point is the key regulator of flowering, FLOWERING LOCUS C (FLC), which has been inferred to explain much of the flowering time variation in Arabidopsis thaliana, yet mutants have been examined in very few backgrounds. We have previously established a set of panspecific flc mutants in 62 accessions of A. thaliana (Ruffley et al. 2024). Here, we investigate how genetic background modulates mutant effects on flowering and vegetative traits, as well as on physiology and transcriptomes. Time to onset of flowering in the genome-edited flc lines was reduced by up to 83%, but considerable variation remained. Genetic mapping showed that extremely early flowering in the absence of FLC was mostly explained by natural variation at the known FLC target FT, with additional contribution from loci colocalizing with FLC. Prognostic sequence analyses of accessions did not suggest that extremely-early combinations of engineered flc and natural FT alleles would be deleterious, yet extremely early flowering accessions are not represented in the commonly used collections of A. thaliana accessions. To test whether this discrepancy could be due to sampling bias, we undertook a focused collection effort of wild populations in Southern Italy, which confirmed that extremely early flowering accessions exist in natural populations. Apart from its specific role in flowering time regulation, FLC has pleiotropic effects on other ecophysiological traits such as growth, and these were also dependent on the genetic background, which was further supported by transcriptomic comparisons. Together we conclude that the various roles of FLC have greatly diversified in different genetic backgrounds. Our study provides a proof-of-concept on how analysis of panspecific mutants can reveal the true extent of genetic networks in which a focal gene participates in.

plant biology↗

bioRxiv2020

The SPIRE1 actin nucleator coordinates actin/myosin functions in the regulation of mitochondrial motility

Subcellular localisation of mitochondria provides a spatial and temporal organisation for cellular energy demands. Long-range mitochondrial transport is mediated by microtubule tracks and associated dynein and kinesin motor proteins. The actin cytoskeleton has a more versatile role and provides transport, tethering, and anchoring functions. SPIRE actin nucleators organise actin filament networks at vesicle membranes, which serve as tracks for myosin 5 motor protein-driven transport processes. Following alternative splicing, SPIRE1 is targeted to mitochondria. In analogy to vesicular SPIRE functions, we have analysed whether SPIRE1 regulates mitochondrial motility. By tracking mitochondria of living fibroblast cells from SPIRE1 mutant mice and splice-variant specific mitochondrial SPIRE1 knockout mice, we determined that the loss of SPIRE1 function increased mitochondrial motility. The SPIRE1 mutant phenotype was reversed by transient overexpression of mitochondrial SPIRE1, which almost completely inhibited motility. Conserved myosin 5 and formin interaction motifs contributed to this inhibition. Consistently, mitochondrial SPIRE1 targeted myosin 5 motors and formin actin filament generators to mitochondria. Our results indicate that SPIRE1 organises an actin/myosin network at mitochondria, which opposes mitochondrial motility. Summary statementThe mitochondrial SPIRE1 protein targets myosin 5 motor proteins and formin actin-filament nucleators/elongators towards mitochondria and negatively regulates mitochondrial motility.

cell biology↗

bioRxiv2020

Proteogenomics analysis of CUG codon translation in the human pathogen Candida albicans

Candida yeasts causing human infections are spread across the yeast phylum with Candida glabrata being related to Saccharomyces cerevisiae, Candida krusei grouping to Pichia spp., and Candida albicans, Candida parapsilosis and Candida tropicalis belonging to the CTG-clade. The latter lineage contains yeasts with an altered genetic code translating CUG codons as serine using a serine-tRNA with a mutated anticodon. It has been suggested that the CTG-clade CUG codons are mistranslated to a small extent as leucine due to mischarging of the serine-tRNA(CAG). The mistranslation was suggested to result in variable surface proteins explaining fast host adaptation and pathogenicity. Here, we re-assessed this potential mistranslation by high-resolution mass spectrometry-based proteogenomics of multiple CTG-clade yeasts, various C. albicans strains, isolated from colonized and from infected human body sites, and C. albicans grown in yeast and hyphal forms. Our in vivo data do not support CUG codon mistranslation by leucine. Instead, (i) CUG codons are mistranslated only to the extent of ribosomal mistranslation with no preference for specific amino acids, (ii) CUG codons are as unambiguous (or ambiguous) as the related CUU leucine and UCC serine codons, (iii) tRNA anticodon loop variation across the CTG-clade yeasts does not result in any difference of the mistranslation level, and (iv) CUG codon unambiguity is independent of C. albicans strain pathogenicity or growth form.

genomics↗

bioRxiv2019

Protein function prediction in genomes: Critical assessment of coiled-coil predictions based on protein structure data

Coiled-coil regions were among the first protein motifs described structurally and theoretically. The beauty and simplicity of the motif gives hope to detecting coiled-coil regions with reasonable accuracy and precision in any protein sequence. Here, we re-evaluated the most commonly used coiled-coil prediction tools with respect to the most comprehensive reference data set available, the entire Protein Data Base (PDB), down to each amino acid and its secondary structure. Apart from the thirtyfold difference in number of predicted coiled-coils the tools strongly vary in their predictions, across structures and within structures. The evaluation of the false discovery rate and Matthews correlation coefficient, a widely used performance metric for imbalanced data sets, suggests that the tested tools have only limited applicability for large data sets. Coiled-coil predictions strongly impact the functional characterization of proteins, are used for functional genome annotation, and should therefore be supported and validated by additional information.

bioinformatics↗

bioRxiv2019

Animal evolution coincides with a novel degree of freedom in exocytic transport processes

Exocytic transport of transmembrane receptors and secreted ligands provides the basis for cellular communication in animals. The RAB8/RAB3/RAB27 trafficking regulators function in transport processes towards the cell membrane. The small G-proteins recruit a diversity of effectors that mediate transport along microtubule and actin tracks, as well as membrane tethering and fusion. SPIRE actin nucleators organise local actin networks at exocytic vesicle membranes. By complex formation with class-5 myosins, vesicle transport track generation and motor protein activation are coordinated. Our phylogenetic analysis traced the onset of SPIRE function back to the origin of the Holozoa. We have identified SPIRE in the closest unicellular relatives of animals, the choanoflagellates, and the more distantly related ichthyosporeans. The discovery of a SPIRE-like protein encoding a KIND and tandem-WH2 domains in the amoebozoan Physarum polycephalum suggests that the SPIRE-type actin nucleation mechanism originated even earlier. Choanoflagellate SPIRE interacts with RAB8, the sole choanoflagellate representative of the metazoan RAB8/RAB3/RAB27 family. Major interactions including MYO5, FMN-subgroup formins and vesicle membranes are conserved between the choanoflagellate and mammalian SPIRE proteins and the choanoflagellate Monosiga brevicollis SPIRE protein can rescue mouse SPIRE1/2 function in melanosome transport. Genome duplications generated two mammalian SPIRE genes (SPIRE1 and SPIRE2) and allowed for the separation of SPIRE protein function in terms of tissue expression and RAB GTPase binding. SPIRE1 is highest expressed in the nervous system and interacts with RAB27 and RAB8. SPIRE2 shows high expression in the digestive tract and specifically interacts with RAB8. We propose that at the dawn of the animal kingdom a new transport mechanism came into existence, which bridges microtubule tracks, detached vesicles and the cellular actin cytoskeleton by organising actin/myosin forces directly at exocytic vesicle membranes. The new degree of freedom in transport may reflect the increased demands of the sophisticated cellular communications in animals.

cell biology↗

bioRxiv2017

The Landscape Of Human Mutually Exclusive Splicing

Mutually exclusive splicing of exons is a mechanism of functional gene and protein diversification with pivotal roles in organismal development and diseases such as Timothy syndrome, cardiomyopathy and cancer in humans. In order to obtain a first genome-wide estimate of the extent and biological role of mutually exclusive splicing in humans we predicted and subsequently validated mutually exclusive exons (MXEs) using 515 publically available RNA-seq datasets. Here, we provide evidence for the expression of over 855 MXEs, 42% of which represent novel exons, increasing the annotated human mutually exclusive exome more than five-fold. The data provides strong evidence for the existence of large and multi-cluster MXEs in higher vertebrates and offers new insights into MXE splicing mechanics and evolution. Finally, MXEs are significantly enriched in pathogenic mutations and their spatio-temporal expression predicts human disease pathology.

bioinformatics↗