Molecular regulation of FMR1 variable transcripts and protein isoforms

• Grant number: 22/07948-9
• Support Opportunities: Regular Research Grants
• Start date: December 01, 2022
• End date: November 30, 2024
• Field of knowledge: Biological Sciences - Morphology - Cytology and Cell Biology
• Principal Investigator: Luciana Amaral Haddad
• Grantee: Luciana Amaral Haddad
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated researchers: Luis Eduardo Soares Netto
• Associated research grant(s): 23/14788-0 - Protein isoform processing, intracellular trafficking and cell vesicular bodies, AP.R SPRINT

Abstract

The FMR1 gene is mutated in fragile X syndrome, the leading inherited cause of intellectual disability among men. FMR1 encodes FMRP, an important RNA-binding protein in synaptic control and neurogenesis. Cerebral corticogenesis appears differentially sensitive to FMR1 mRNA and protein amounts. Distinct post-transcriptional mechanisms regulate the stability of the FMR1 transcript. As FMR1 pre-mRNA may undergo alternative splicing, variable out-of-frame transcripts can potentially lead to auto-regulatory feedback loops onto its mRNA stability. We previously observed in the rat forebrain high amounts of total Fmr1 mRNA and long FMRP isoforms on E11-E18 and P2-P7 developmental days, and their lowest levels on E19-E20 and beyond P14. Fmr1 exon 14 can be alternatively skipped shifting the translational reading frame, and exon 15 has three splice acceptor sites. We formerly disclosed significant exon-14 skipping in E17-E20 rat forebrain and low levels of the resulting messages with exon 13-15 junctions, although they appeared not subject to degradation triggered by the nonsense-mediated decay (NMD). Here, we propose to investigate additional pathways that may elicit the degradation of FMR1 messages with junctions between exons 13 and 15. We previously identified a protein-protein interaction network for FMRP. Based on this evidence, here we aim to evaluate the non-canonical subcellular distribution of FMRP isoforms and how it is regulated. (AU)