Saravanan, H. | bioRxiv Science

bioRxiv2023

The myocardium utilizes Pdgfra-PI3K signaling to steer towards the midline during heart tube formation

Coordinated cell movement is a fundamental process in organ formation. During heart development, bilateral myocardial precursors collectively move towards the midline (cardiac fusion) to form the primitive heart tube. Along with extrinsic influences such as the adjacent anterior endoderm which are known to be required for cardiac fusion, we previously showed that the platelet-derived growth factor receptor alpha (Pdgfra) is also required. However, an intrinsic mechanism that regulates myocardial movement remains to be elucidated. Here, we uncover an essential intrinsic role in the myocardium for the phosphoinositide 3-kinase (PI3K) intracellular signaling pathway in directing myocardial movement towards the midline. In vivo imaging reveals that in PI3K-inhibited zebrafish embryos myocardial movements are misdirected and slower, while midline-oriented dynamic myocardial membrane protrusions become unpolarized. Moreover, PI3K activity is dependent on and genetically interacts with Pdgfra to regulate myocardial movement. Together our findings reveal an intrinsic myocardial steering mechanism that responds to extrinsic cues during the initiation of cardiac development.

developmental biology↗

bioRxiv2021

A nuclear function for an oncogenic microRNA as a modulator of snRNA and splicing

miRNAs are regulatory transcripts established as repressors of mRNA stability and translation. Here we demonstrate that a key onco-miRNA, miR-10b, binds to U6 snRNA, a core component of the spliceosomal machinery. We provide evidence of direct binding between miR-10b and U6, in situ visualizations of miR-10b and U6 co-localization in glioma cells and patient-derived tumor tissues, and biochemical co-isolation of miR-10b with the components of the spliceosome. We further demonstrate that miR-10b modulates U6 N-6-adenosine methylation and pseudouridylation, U6 binding to splicing factors SART3 and PRPF8, and regulates U6 stability, conformation, and levels. These effects on U6 result in splicing alterations, illustrated by the altered ratio of the isoforms of a small GTPase CDC42, reduced overall CDC42 levels, and downstream CDC42 -mediated effects on cell viability. We, therefore, present an unexpected intersection of the miRNA and splicing machineries and a new nuclear function for a major cancer-associated miRNA.

molecular biology↗