The Identification of Nuclear FMRP Isoform Iso6 Partners

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Fragile X Syndrome (FXS) stems from FMRP deficiency, impacting neurodevelopment.
• FMRP has distinct cytoplasmic (iso1) and nuclear (iso6) isoforms with different functions.
• Nuclear FMRP isoforms are implicated in DNA damage response, regulating genomic instability.

Purpose of the Study:

• To identify and characterize the interaction partners of the nuclear FMRP isoform iso6.
• To investigate the specificity of interactions between nuclear and cytoplasmic FMRP isoforms.
• To elucidate the role of nuclear FMRP in DNA damage response, particularly under replication stress.

Main Methods:

• Affinity purification coupled with mass spectrometry (AP-MS) to map the nuclear interactome of FMRP iso6 in U2OS cells.
• Comparative analysis of interaction partners between nuclear iso6 and cytoplasmic iso1 FMRP isoforms.
• Assessment of interaction regulation by replication stress and proteasomal targeting.

Main Results:

• Identified nuclear FMRP iso6 interactors involved in RNA processing, splicing, ribosome biogenesis, DNA replication/damage response, chromatin remodeling, and chromosome segregation.
• Discovered a subset of proteins binding specifically to nuclear iso6, including DNA-associated and proteasomal proteins.
• Demonstrated that nuclear iso6 interactions are regulated by replication stress, unlike cytoplasmic iso1 interactions.
• Showed that the proteasome targets nuclear FMRP iso6.

Conclusions:

• Nuclear FMRP isoforms possess distinct functions, particularly in DNA damage response, separate from cytoplasmic isoforms.
• Nuclear FMRP iso6 interacts with specific partners involved in DNA-associated processes and is regulated by replication stress and proteasomal degradation.
• These findings highlight a novel role for nuclear FMRP in maintaining genomic stability during replication stress.