Nielsen, A. C. | Search bioRxiv

bioRxiv2024

A modular system for programming multistep activation of endogenous genes in stem cells

Although genomes encode instructions for mammalian cell differentiation with rich syntactic relationships, existing methods for genetically programming cells have modest capabilities for stepwise regulation of genes. Here, we developed a sequential genetic system that enables transcriptional activation of endogenous genes in a preprogrammed, stepwise manner. The system relies on the removal of an RNA polymerase III termination signal to induce both the transcriptional activation and the DNA endonuclease activities of a Cas9-VPR protein to effect stepwise progression through cascades of gene activation events. The efficiency of the cascading system enables a new dimension for cellular programming by allowing the manipulation of the sequential order of gene activation for directing the differentiation of human stem cells. One-Sentence SummaryDevelopment of a synthetic biology system for preprogrammed, stepwise activation of endogenous genes.

synthetic biology↗

bioRxiv2024

The Pannexin-1 N-terminal Helix Gates a Switch between Ion Conductance and Anandamide Transport

Anandamide is an endovanilloid and endocannabinoid with ligand activity at transient receptor potential vanilloid 1 channels and cannabinoid receptors, respectively. We have reported that block of Pannexin-1 channels in the CA1 hippocampus can increase concentrations of anandamide and induce presynaptic plasticity. It is not known how an ion channel can contribute to clearance of a lipid-derived signalling molecule. Here, we use electrophysiology and imaging of uptake of fluorescent anandamide to determine the structure-function relationship between the ion conduction and anandamide trasporter activities of pannexin-1. Expression of rat, mouse or human pannexin-1 in HEK cells caused a time dependent increase in anandamide uptake by all three orthologs. However, human pannexin-1 had reduced ion conduction. Low concentrations of anandamide augmented uptake of its fluorescent derivative, whereas higher concentrations competed, suggesting that anadamide may facilitate its own transport. Deletion of the N-terminal helix of pannexin-1 and the channel blocker, probenecid, blocked ion conduction but enhanced anandamide transport. In contrast, mutation of pore facing isoleucine 41 caused a gain of function in ion conduction with loss of anandamide transport. We conclude that the pannexin-1 channel is a dual ion channel / anandamide transporter and that these properties are gated by the channels N-terminal helix and likely linked to its presence or absence within the pore lining region.

neuroscience↗