Expression and misexpression of the miR-183 family in the developing hearing organ of the chicken
The miR-183 family consists of 3 related microRNAs (miR-183, miR-96 and miR-182) that are required for the proper maturation of primary sensory cells in both the inner ear and the retina in mammals. The miR-183 family shows dynamic longitudinal and radial gradients in the developing mouse cochlea, which raises a question whether the microRNA levels play a role in specifying hair cell phenotypes. To answer this question, I used the chicken inner ear to study expression and misexpression of the miR-183 family. In this study, I reported the differential gene expression of the miR-183 family through development in the embryonic chicken inner ear by in situ hybridization. The spatiotemporal expression patterns of all three miRNAs were similar. At E7, labeled hair cells were present in several vestibular sensory organs. At the same age, expression was detectable in the apex of the basilar papilla with differentiated hair cells, and a weak radial gradient was seen with the highest expression on the superior side in the base of the basilar papillae with undifferentiated precursors. At E12-E18, the higher packing density of tall hair cells located on the superior basilar papilla suggested the persistence of a radial gradient from the surface view. However, sections through the basilar papillae suggested that the miRNA levels appeared to be similar on the superior and inferior sides. On the other hand, a longitudinal gradient was observed at E16-E18: levels were higher in the apex than the base. The functional role of the expression gradients in the basilar papillae was tested by overexpression of the miR-183 family using Tol2 transposase-mediated stable expression of the miRNAs. Electroporation of plasmids into the E2-E3 otocyst did not affect hair cell morphologies along the longitudinal axis 11-14 days later, nor did it affect the differentiation of tall versus short hair cells across the radial axis. Instead, midway along the longitudinal axis, there appeared to be a higher incidence of electroporated hair cells relative to supporting cells, indicating a slight bias toward a hair cell fate. Therefore, the manipulation of the miR-183 family could influence cell lineage decisions, but it was insufficient to direct the differentiation of hair cells towards specific radial or longitudinal phenotypes. As a first step toward cataloging potential downstream genes regulated by members of this hair-cell-enriched miRNA family, I performed luciferase assays in vitro and verified 14 human gene targets of miR-182.
Fekete, Purdue University.
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