Left-Right Patterning: Biophysical and Chemical Signaling Pathways that Contribute to Left-Right Axis Establishment
Loading...
Date
2024-08-07
Authors
Luna-Arvizu, Gabriel
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Cells sense their environment by detecting and responding to mechanical forces and chemical signals across their surface. Fluid flows, which can impart force and distribute chemicals, are critical for organ development, embryonic patterning, and contribute to host-microbe interactions and cancer metastasis. Despite the impacts on human health, flow signal sensation is understudied. We aim to elucidate how embryos break left-right (L-R) symmetry using flow-derived signals to understand cell communication. During development, beating cilia within structures called L-R organizers (LRO) generate an asymmetric flow that breaks symmetry. Cells sense flow, repressing the target gene dand5 on the left side only. The response to flow signals involves cilia yet mechanisms remain unclear. Our main hypothesis is that the Polycystin transmembrane protein Pkd1l1 complexes with cation channel Pkd2 to mediate flow signal sensation and establish L-R asymmetries. We found that pkd1l1 zebrafish mutants exhibited L-R defects in the heart, brain, pancreas, as well as displaying aberrant laterality-associated behaviors. Spatiotemporally, pkd1l1 and dand5 are co-expressed during flow stages. Global and cell-specific mutagenesis revealed Pkd1l1 functions cell-autonomously to maintain high levels of dand5, suggesting that flow normally represses Pkd1l1 on the left, leading to reduced dand5 on that side. Flow signals are thought to open Pkd2 channels, resulting in intraciliary Ca2+ signals. Mutation of pkd1l1 led to increased intraciliary Ca2+ signals, supporting a model in which Pkd1l1 represses Pkd2 channels until that repression is relieved by flow on the left.A second goal of this thesis was to discover novel causes of human laterality diseases. Recently, our team discovered DIXDC1 mutations in families exhibiting heterotaxia and situs inversus i.e. defective L-R symmetry breaking. Dixdc1 is thought to play a role in Wnt signaling, but had not previously been linked to L-R patterning. Using loss and gain of function approaches, we determined that perturbation of dixdc1a and dixdc1b, two zebrafish paralogs of DIXDC1, caused edema, abnormal body axis development, reduced forebrain and, importantly, severe heart laterality defects. Molecular evidence suggests dixdc1a and dixdc1b act upstream of dand5. Thus, we have uncovered a new role for the Wnt regulator Dixdc1 in L-R patterning across species. This further establishes an interplay between mechanical and chemical signals that orchestrate the breaking of symmetry during development.
This dissertation includes previously published co-authored material.
Description
Keywords
Asymmetry, Cilia, dand5, Left-right, Pkd1l1, Symmetry