Biology subjects

Bittermann, E.

Publications and source records attributed to Bittermann, E..

3 recordsLinked to original sources

bioRxiv2025

Bottlenecks and Resistance Evolution against an Antimicrobial 1 Peptide

Bottlenecks - a severe reduction in population size--are ubiquitous for bacteria in natural systems. For example, during the complete metamorphosis of insects, the gut microbiota is bottlenecked due to a massive secretion of immune effectors such as antimicrobial peptides (AMPs) into the gut. However, the effect of natural bottlenecks on resistance evolution of bacteria to AMPs is currently unknown. Here we measured the bottlenecking of the gut microbiota of G. mellonella, the greater wax moth. Based on these population estimates, we tested in vitro the influence of population size on the adaptation of E. coli against an AMP. We used wild-type E. coli and mutator strains with a 100-fold increase in mutation rates to partly disentangle population size from mutant supply. We found that large E. coli mutator strain populations evolved higher resistance than small populations. Population size, however, did not affect adaptation in wild-type strains. They were not able to evolve resistance under our experimental conditions. This shows that natural bottlenecks can benefit insect hosts by combating the evolution of AMP resistance to their resident gut microbiota, but this should also be applicable to infection in other organisms that use AMPs as an immune defense.

evolutionary biology↗

bioRxiv2022

Dkk1 inhibition normalizes limb phenotypes in a mouse model of Fzd2 associated omodysplasia Robinow syndromes

FRIZZLED-2 (FZD2) is a transmembrane Wnt ligand receptor. We previously identified a pathogenic human FZD2 variant, encoding for a protein with a premature stop and loss of 17 amino acids. This includes a portion of the consensus DISHEVELLED binding sequence required for Wnt signal transduction. Patients with this variant exhibited FZD2-associated autosomal dominant Robinow Syndrome. To model this variant, we utilized zygote microinjection and i-GONAD-based CRISPR/Cas9-mediated genome editing to generate an allelic series in the mouse. Embryos mosaic for humanized Fzd2W553* knock-in exhibited cleft palate and shortened limbs, consistent with FZD2W548* patient phenotypes. We also generated two germline mouse alleles with small deletions, Fzd2D3 and Fzd2D4. Homozygotes for each allele survive embryonic development at normal ratios but exhibit a highly penetrant cleft palate phenotype, shortened limbs compared to wild-type and perinatal lethality. Fzd2D4 craniofacial tissues indicated decreased canonical WNT signaling. In utero treatment with IIIC3a (DKK inhibitor) normalized the limb lengths in Fzd2D4 homozygotes. The in vivo replication represents an approach to further investigate the mechanism of FZD2 phenotypes and validates the utility of CRISPR knock-in mice as a tool for demonstrating pathogenicity of human genetic variants. We also present evidence for a potential therapeutic intervention.

developmental biology↗

bioRxiv2018

Differential requirements of tubulin genes in mammalian forebrain development.

Tubulin genes encode a series of homologous proteins used to construct microtubules which are essential for multiple cellular processes. Neural development is particularly reliant on functional microtubule structures. Tubulin genes comprise a large family of genes with very high sequence similarity between multiple family members. Human genetics has demonstrated that a large spectrum of cortical malformations results from de novo heterozygous mutations in tubulin genes. However, the absolute requirement for most of these genes in development and disease has not been previously tested in genetic, loss of function models. Here we present two novel pathogenic tubulin alleles: a human TUBA1A missense variant with a phenotype more severe than most tubulinopathies and a mouse ENU allele of Tuba1a. Furthermore, we directly test the requirement for Tuba1a, Tuba8, Tubb2a and Tubb2b in the mouse by deleting each gene individually using CRISPR-Cas9 genome editing. We show that loss of Tuba8, Tubb2a or Tubb2b does not lead to cortical malformation phenotypes or impair survival. In contrast, loss of Tuba1a is perinatal lethal and leads to significant forebrain dysmorphology. Thus, despite their functional similarity, the requirements for each of the tubulin genes and levels of functional redundancy are quite different throughout the gene family. The ability of the mouse to survive in the absence of some tubulin genes known to cause disease in humans suggests future intervention strategies for these devastating tubulinopathy diseases.

developmental biology↗