Dardari, H. | bioRxiv Science

bioRxiv2026

Genetic compensation in β-actin mutants occurs independently of mutations that destabilize β-actin mRNA

Proper maintenance of gene expression in response to mutations or environmental fluctuations is critical for cell development and survival. Recently, a novel genetic compensation mechanism was described wherein mutant mRNA decay triggers increased transcription of paralogous genes. This effect was reported for several genes, including {beta}-actin (Actb) in mouse embryonic stem cells, where Actb mRNA with a premature termination codon enhances transcription of its paralog, {gamma}-actin (Actg1), and partially rescues cytoskeletal defects. Here we show that, in both mouse and human embryonic stem cells, mutations in the ACTB gene, regardless of mutant mRNA expression, trigger genetic compensation. Furthermore, transgenic expression of mutant ACTB mRNA with a premature stop codon fails to induce genetic compensation. Depletion of the SRF or MRTF-A transcription factors, which are known to increase ACTB transcription in response to low ACTB protein levels, diminishes the genetic compensation response in ACTB mutants. These results suggest that genetic compensation in ACTB mutants is primarily mediated by a transcriptional feedback loop via SRF/MRTF-A, independent of the expression or degradation of mutant ACTB mRNA.

molecular biology↗

bioRxiv2023

Cholesterol regulates plasma membrane bending by prominin-family proteins

Prominin-1 (Prom1) is a five-transmembrane-pass integral membrane protein that associates with curved regions of the plasma membrane. Prom1 interacts with membrane cholesterol and actively remodels the plasma membrane. Membrane bending activity is particularly evident in photoreceptors, where Prom1 loss-of-function mutations cause failure of outer segment homeostasis, leading to cone-rod retinal dystrophy (CRRD). The Tweety Homology (Ttyh) protein family has been proposed to be homologous to Prominin, but it is not known whether Ttyh proteins have an analogous membrane-bending function. Here, we characterize the membrane-bending activity of human Prom1 and Ttyh1 in native bilayer membranes. We find that Prom1 and Ttyh1 both induce formation of extracellular vesicles (EVs) in cultured mammalian cells and that the EVs produced are physically similar. Ttyh1 is more abundant in EV membranes than Prom1 and produces EVs with membranes that are more tubulated than Prom1 EVs. We further show that Prom1 interacts more stably with membrane cholesterol than Ttyh1 and that this may contribute to membrane bending inhibition in Prom1 EVs. Intriguingly, a loss-of-function mutation in Prom1 associated with CRRD induces particularly stable cholesterol binding. These experiments provide mechanistic insight into Prominin function in CRRD and suggest that Prom and Ttyh belong to a single family of functionally related membrane-bending, EV-generating proteins.

biochemistry↗