Biology subjects

Hemmerich, C.

Publications and source records attributed to Hemmerich, C..

3 recordsLinked to original sources

bioRxiv2026

Histone H3K9 Methyltransferases Regulate Cortical Growth by Coordinating Heterochromatin Formation and Neural Progenitor Dynamics

DNA packaging into heterochromatin is a fundamental mechanism of transcriptional silencing. However, how heterochromatin regulates neurogenesis in the developing cerebral cortex remains poorly understood. A defining feature of heterochromatin is trimethylation of histone H3 lysine 9 (H3K9me3), catalyzed by the H3K9 methyltransferases SETDB1, SUV39H1, and SUV39H2. Here, we generate a cortex-specific triple knockout mouse model lacking Setdb1, Suv39h1, and Suv39h2 to interrogate the collective functions of H3K9 methyltransferases and H3K9me3 during corticogenesis. Loss of H3K9 methyltransferases disrupts cell-cycle dynamics and cortical neurogenesis, resulting in microcephaly. We show that H3K9me3 is associated with the silencing of distinct gene families, lineage-inappropriate genes, and transposable elements, and that its loss is accompanied by local chromatin opening and enhanced transcription factor occupancy. Our findings suggest that H3K9me3 regulates neurogenesis in part by silencing the growth-inhibitory gene Cdkn1c in intermediate progenitors. These results underscore the critical role of heterochromatin in the temporal control of neurogenesis.

developmental biology↗

bioRxiv2021

The polar flagellar transcriptional regulatory network in Vibrio campbellii deviates from canonical Vibrio species

Vibrio campbellii is a Gram-negative bacterium that is free-living and ubiquitous in marine environments, and it is a pathogen of fish and shellfish. Swimming motility via a single polar flagellum is a critical virulence factor in V. campbellii pathogenesis, and disruption of the flagellar motor significantly decreases host mortality. To examine V. campbellii flagellar gene regulation, we identified homologs of flagellar and chemotaxis genes conserved in other members of the Vibrionaceae and determined the transcriptional profile of these loci using differential RNA-seq. We systematically deleted all 63 predicted flagellar and chemotaxis genes in V. campbellii and examined their effects on motility and flagellum production. We specifically focused on the core flagellar regulators of the flagellar regulatory hierarchy established in other Vibrios: RpoN ({sigma}54), FlrA, FlrC, and FliA. Our results show that V. campbellii transcription of flagellar and chemotaxis genes is governed by a multi-tiered regulatory hierarchy similar to other motile Vibrio species but with two critical differences: the {sigma}54-dependent regulator FlrA is dispensable for motility, and Class II gene expression is independent of {sigma}54 regulation. Our genetic and phenotypic dissection of the V. campbellii flagellar regulatory network highlights the differences that have evolved in flagellar regulation across the Vibrionaceae.

microbiology↗

bioRxiv2020

High-Resolution Phylogenetic and Population Genetic Analysis of Microbial Communities with RoC-ITS

Microbial communities are inter-connected systems of incredible complexity and dynamism that play crucial roles in health, energy, and the environment. To better understand microbial communities and how they respond to change, it is important to know which microbes are present and their relative abundances at the greatest taxonomic resolution possible. Here, we describe a novel protocol (RoC-ITS) that uses the single-molecule Nanopore sequencing platform to assay the composition of microbial communities in unprecedented detail. This methodology produces long-read sequences including multiple copies of the same complete 16S ribosomal gene and its neighboring internally transcribed spacer (ITS) using rolling-circle amplification. The ribosomal 16S gene provides phylogenetic information down to the species-level, while the much less conserved ITS region contains strain-level information. When linked together, this combination of markers allows for the identification of individual ribosomal units within a specific organism, the assessment of their relative stoichiometry, and the ability to monitor subtle shifts in microbial community composition with a single generic assay. We applied RoC-ITS to a mock microbial community that was also sequenced using the Illumina platform, demonstrating its accuracy in quantifying the relative abundance and identity of each species.

genomics↗