Talk abstracts
Talk on Friday 02:15-02:30pm submitted by Fatimah Matalkah
The Musashi family of stem cell factors is critical for the survival and function of terminally differentiated photoreceptor neurons.
Fatimah Matalkah (Biochemistry/WVU), Bohye Jeong (Biochemistry/WVU), Visvanathan Ramamurthy (Biochemistry/WVU), Peter Stoilov (Biochemistry/WVU)
Abstract:
The Musashi (MSI) proteins are RNA binding proteins consisting of two paralogs MSI1/2 that are highly conserved across species. The MSI proteins are known for their role in maintaining undifferentiated state of stem cells. In the context of mature retina, we show that MSI proteins maintain high expression level with a distinct switch occurring between MSI1 and MSI2 expression during postnatal development. Our observations reveal a new role for the MSI proteins in terminally differentiated cells. To understand the role of the MSI in mature photoreceptors we utilized an inducible mouse knockout model that allows for the timed deletion of MSI at postnatal day 30. Ablation of the MSI proteins in the fully developed photoreceptors caused progressive loss of vision. The results demonstrate that the MSI are required for the maintenance of the differentiated photoreceptors and functionally can compensate for each other. To investigate the molecular mechanism, we used CLIP-Seq to identify MSI1 targets and the binding sites in the retinal transcriptome. CLIP-Seq revealed MSI binding to the 3’-UTR of large number of transcripts. Among the identified targets are proteins that are involved in the phototransduction pathway or are critical for the maintenance of photoreceptors outer segment structure. Proteomics analysis showed deletion of the MSI results in a significant reduction in proteins involved in the phototransduction pathway including RHO, GNB1, and GNAT1 with a significant increase in GFAP and STAT3. Interestingly, the results also detected on protein level a switch in the alternative splicing that we previously detected by RNA-Seq. Closer examination of the protein levels of MSI targets revealed that the MSI function as translational activator. Thus, we hypothesize that the high expression of MSI proteins in mature retina is evolutionary meant to keep up with the high demand of protein synthesis that is required to maintain the constant regeneration of the light receptive organelle of the photoreceptors. Importantly, the protein expression from a significant proportion of the MSI bound mRNA is not affected by the loss of MSI. This observation implies that MSI is either acting in cooperation with additional factors, or there is a built-in redundancy in the translational regulation of many of the MSI bound transcripts.
Keywords: Musashi, RNA binding proteins, Photoreceptors