ELAVL1 and ELAVL4 are required for Musashi-dependent translational activation

Area of Science:

• Molecular Biology
• Developmental Biology
• RNA Biology

Background:

• Musashi1 and Musashi2 (MSI1, MSI2) are RNA-binding proteins crucial for stem cell function and tissue plasticity.
• MSI proteins typically act as translational repressors but can also activate mRNA translation in specific contexts.
• The precise mechanisms underlying MSI-mediated translational activation remain largely unknown.

Purpose of the Study:

• To elucidate the molecular mechanism of MSI-mediated mRNA translational activation.
• To identify novel co-regulators involved in MSI1-dependent translational activation.
• To investigate the evolutionary conservation and functional significance of this regulatory pathway.

Main Methods:

• Antisense oligonucleotide knockdown in *Xenopus laevis* oocytes.
• Functional rescue assays with exogenous protein expression.
• RNA-independent interaction studies using protein domains.
• Mass spectrometry for interaction analysis.
• Reporter assays in mammalian cell lines.

Main Results:

• Embryonic Lethal Abnormal Vision-like (ELAVL) proteins were identified as essential co-regulators of MSI1-dependent translational activation.
• Knockdown of *Elavl4* in *Xenopus* oocytes inhibited maturation and blocked translation of MSI target mRNAs (*Mos*, *Cyclin B5*).
• ELAVL4 C-terminal domain interacts with MSI1 N-terminal RNA recognition motifs in an RNA-independent manner.
• This interaction is conserved across species, with human ELAVL1 rescuing *Elavl4*-depleted oocytes and mouse ELAVL1 interacting with MSI1 in the pituitary.
• Knockdown of *Elavl1* in mammalian cells abrogated MSI-dependent translational activation of a *Prop1* mRNA reporter.

Conclusions:

• ELAVL proteins are critical partners for MSI1 in promoting mRNA translational activation.
• This ELAVL-MSI interaction is an evolutionarily conserved mechanism essential for cell cycle progression and potentially tissue plasticity.
• The findings reveal a novel pathway for post-transcriptional gene regulation mediated by RNA-binding proteins.