|M.Sc Student||Daria Rashkovetsky|
|Subject||Characterization of MicroRNA-184 Expression and Pathways|
during Skin and Corneal Development and
|Department||Department of Medicine||Supervisors||Professor Shalom-Feuerste Ruby|
|Full Professor Aberdam Daniel|
|Full Thesis text|
The epidermis and the corneal epithelium are stratified epithelia that develop from the surface ectoderm and function as a barrier against exterior insults. The extraordinary dynamic replenishment of these tissues depends on very similar epithelial stem cells that give-rise to progenitors that proliferate, differentiate, while migrating towards the tissue surface where they become terminally differentiated and die. Elucidating the molecular circuitry of stem cells and their regulation is required for understanding the etiology of numerous epithelial diseases and may pave the way for efficient regenerative medicine.
MicroRNAs (miRNAs) play a role in various physiological processes including embryogenesis, tissue regeneration and diseases. Here, we report that miR-184, a highly evolutionary conserved miRNA, regulates epithelial homeostasis. In situ hybridization analysis revealed that miR-184 is predominantly expressed in the adult mouse cornea, the developing lens, epidermis and hair follicles. Interestingly, the expression of miR-184 was restricted to early differentiated cells in vivo and in vitro but was absent from the compartments of stem cells or terminally differentiated cells. In addition, we showed that miR-184 is reciprocally expressed with the stem cell marker K15, in line with previous research in our laboratory which showed that miR-184 can bind to the K15 untranslated region. The study of keratinocyte cellular model showed the ability of miR-184 to repress K15 expression, cell proliferation and induce differentiation. This was correlated with an increase in Wnt/β-catenin and Notch pathways, which play a key role in the activation of epithelial stem cells and their differentiation. Next, we have generated and investigated a new miR-184 knockout mouse model. miR-184-null mice did not display gross skin phenotypes although we detected abnormal differentiation that was hallmarked by reduction in the differentiation marker K10. Interestingly, we observed apparent disorganized eye structure coupled with a reduction in the extracellular protein Laminin in the corneal epithelium, basal lamina and endothelium. These apparent phenotypes require further investigation, however, in agreement with our findings, it was recently reported that a point mutation at the seed sequence of MIR184 was linked with eye syndromes affecting the cornea and the lens, thus, opens new directions for future research.
Altogether, these data supports the hypothesis that miR-184 is involved in the exit from ‘stemness’ state and regulation of skin/corneal morphogenesis and homeostasis.