Wetzel, L. A. | Search bioRxiv

bioRxiv2024

Chromatin profiling identifies putative dual roles for H3K27me3 in regulating transposons and cell type specific genes in choanoflagellates

Gene expression is tightly controlled during animal development to allow the formation of specialized cell types. Our understanding of how animals evolved this exquisite regulatory control remains elusive, but evidence suggests that changes in chromatin-based mechanisms may have contributed. To investigate this possibility, here we examine chromatin-based gene regulatory features in the closest relatives of animals, choanoflagellates. Using Salpingoeca rosetta as a model system, we examined chromatin accessibility and histone modifications at the genome scale and compared these features to gene expression. We first observed that accessible regions of chromatin are primarily associated with gene promoters and found no evidence of distal gene regulatory elements resembling the enhancers that animals deploy to regulate developmental gene expression. Remarkably, a histone modification deposited by polycomb repressive complex 2, histone H3 lysine 27 trimethylation (H3K27me3), appeared to function similarly in S. rosetta to its role in animals, because this modification decorated genes with cell type-specific expression. Additionally, H3K27me3 marked transposons, retaining what appears to be an ancestral role in regulating these elements. We further uncovered a putative new bivalent chromatin state at cell type-specific genes that consists of H3K27me3 and histone H3 lysine 4 mono-methylation (H3K4me1). Together, our discoveries support the scenario that gene-associated histone modification states that underpin development emerged before the evolution of animal multicellularity.

evolutionary biology↗

bioRxiv2018

TgCentrin2 is required for invasion and replication in the human parasite Toxoplasma gondii

Centrins are EF-hand containing proteins ubiquitously found in eukaryotes and are key components of centrioles/basal bodies as well as certain contractile fibers. We previously identified three centrins in the human parasite Toxoplasma gondii, all of which localized to the centrioles. However, one of them, TgCentrin2 (CEN2), is also targeted to ring-shaped structures at the apical and basal ends of the parasite, as well as to multiple annuli at the junction between the apical cap and the rest of the membrane cortex. The role(s) that TgCentrin2 plays in these locations was unknown. Here we report the functional characterization of TgCentrin2 in the parasite lytic cycle. After multiple unsuccessful attempts to knock out or knock down the TgCentrin2 gene with existing tools, we designed a new conditional knockdown method that combines transcriptional and protein stability control to achieve tight regulation of TgCentrin2 levels in the parasite. We discovered that under knockdown conditions, there was an ordered loss of TgCentrin2 from its four compartments, due to differences in incorporation kinetics and structural inheritance over successive generations. This was correlated with the development of major invasion deficiency at early stages of CEN2 knockdown, and replication defects at later stages. These results indicate that TgCentrin2 is incorporated into multiple cytoskeletal structures to serve distinct functions in T. gondii that are required for parasite survival.

cell biology↗