Biology subjects

Harmon, R. M.

Publications and source records attributed to Harmon, R. M..

3 recordsLinked to original sources

bioRxiv2022

Transcriptional profiling of rare acantholytic disorders suggests common mechanisms of pathogenesis

BackgroundDarier, Hailey-Hailey, and Grovers diseases are rare non-autoimmune acantholytic skin diseases. While these diseases have different underlying causes, they share defects in cell-cell adhesion in the epidermis and desmosome organization. ObjectiveTo better understand the underlying mechanisms leading to disease in these conditions we performed RNA-seq on lesional skin samples from Darier, Hailey-Hailey, and Grovers disease patients. MethodsRNA-seq and bioinformatics analyses were performed on banked paraffin embedded diagnostic samples from each disease. For detailed Methods, please see the Methods section in this articles Online Repository at www.jacionline.org. ResultsThe transcriptomic profiles of Darier, Hailey-Hailey, and Grovers disease were found to share a remarkable overlap, which did not extend to other common inflammatory skin diseases, psoriasis and atopic dermatitis. Analysis of enriched pathways showed a shared upregulation in keratinocyte differentiation and Th17 inflammatory pathways, and a decrease in cell adhesion and actin organization pathways in Darier, Hailey-Hailey, and Grovers disease. Direct comparison to atopic dermatitis and psoriasis showed that the downregulation in actin organization pathways was a unique feature in Darier, Hailey-Hailey, and Grovers disease. Further, upstream regulator analysis suggests that a decrease in SRF/MRTF activity may be responsible for the downregulation of actin organization pathways. Staining for MRTFA in lesional skin samples showed a decrease in nuclear MRTFA in patient skin compared to normal skin. ConclusionThese findings highlight the significant level of similarity in the transcriptome of Darier, Hailey-Hailey, and Grovers disease, and identify decreases in actin organization pathways as a unique signature present in these conditions. Key MessagesO_LIDarier Disease, Hailey-Hailey Disease, and Grovers Disease share similar transcriptional profiles suggesting common mechanisms of pathogenesis. C_LIO_LISRF/MRTFA activity is reduced in Darier Disease, Hailey-Hailey Disease and Grovers disease, implicating actin organization in acantholysis. C_LI

genomics↗

bioRxiv2021

Asymmetric Contraction of Adherens Junctions arises through RhoA and E-cadherin feedback

Tissue morphogenesis often arises from the culmination of discrete changes in cell-cell junction behaviors, namely ratcheted junction contractions that lead to collective cellular rearrangements. Mechanochemical signaling in the form of RhoA underlies these ratcheted contractions, which occur asymmetrically as one highly motile vertex contracts toward a relatively less motile tricellular vertex. The underlying mechanisms driving asymmetric vertex movement remains unknown. Here, we use optogenetically controlled RhoA in model epithelia together with biophysical modeling to uncover the mechanism lending to asymmetric vertex motion. We find that both local and global RhoA activation leads to increases in junctional tension, thereby facilitating vertex motion. RhoA activation occurs in discrete regions along the junction and is skewed towards the less-motile vertex. At these less-motile vertices, E-cadherin acts as an opposing factor to limit vertex motion through increased frictional drag. Surprisingly, we uncover a feedback loop between RhoA and E-cadherin, as regional optogenetic activation of specified junctional zones pools E-cadherin to the location of RhoA activation. Incorporating this circuit into a mathematical model, we find that a positive feedback between RhoA-mediated tension and E-cadherin-induced frictional drag on tricellular vertices recapitulates experimental data. As such, the location of RhoA determines which vertex is under high tension, pooling E-cadherin and increasing the frictional load at the tricellular vertex to limit its motion. This feedback drives a tension-dependent intercellular "clutch" at tricellular vertices which stabilizes vertex motion upon tensional load.

cell biology↗

bioRxiv2021

Dia1 Coordinates Differentiation and Cell Sorting in a Stratified Epithelium

Although implicated in adhesion, few studies address how actin assembly factors guide cell positioning in multicellular tissue. The formin, Dia1, localizes to the proliferative basal layer of epidermis. In organotypic cultures, Dia1 depletion reduced basal cell density and resulted in stratified tissue with disorganized differentiation and proliferative markers. Since crowding induces differentiation in epidermal tissue, we hypothesized that Dia1 allows cells to reach densities amenable to differentiation prior to stratification. Consistent with this hypothesis, forced crowding of Dia1-deficient cells rescued transcriptional abnormalities. Dia1 promotes rapid growth of lateral adhesions, a behavior consistent with the ability of cells to remain monolayered when crowded. In aggregation assays, cells sorted into distinct layers based on Dia1 expression status. These results suggested that as basal cells proliferate, reintegration and packing of Dia1-positive daughter cells is favored while Dia1-negative cells tend to delaminate to a suprabasal compartment. These data demonstrate how formin expression patterns play a crucial role in constructing distinct domains within stratified epithelia. SummaryHarmon et al demonstrate that differential expression of an actin nucleator, the formin, Dia1, drives cell sorting and maintains distinct morphological domains within an epithelial tissue. This illuminates the possible utility of evolving a large formin family in orchestrating the compartmentalization and differentiation of complex tissues.

cell biology↗