The exon junction complex is required for stem and progenitor cell maintenance in planarians

Area of Science:

• Molecular Biology
• Developmental Biology
• Regenerative Medicine

Background:

• The exon junction complex (EJC) is known to regulate RNA processing, including mRNA export and translation.
• While broadly found on spliced mRNAs, the EJC's specific functions are increasingly linked to gene-specific roles.
• Previous studies suggest EJC involvement in stem cell maintenance in model organisms like Drosophila and mice.

Purpose of the Study:

• To investigate the role of the EJC in the regeneration process of the planarian flatworm Schmidtea mediterranea.
• To determine if EJC function is essential for the maintenance of stem and progenitor cells during regeneration and normal tissue turnover.

Main Methods:

• Utilized a classroom-based RNA interference (RNAi) screen in Schmidtea mediterranea.
• Assessed the impact of EJC subunit inhibition on regeneration and cell turnover.
• Analyzed gene expression changes in differentiated tissues post-amputation.

Main Results:

• RNAi-mediated knockdown of EJC subunits led to rapid loss of stem and progenitor cells in planarians.
• This loss of stem cells impaired both regeneration and normal tissue turnover.
• Differentiated tissues showed normal responses to amputation-induced gene expression changes, indicating a specific role for EJC in stem cell populations.
• These findings align with previous observations of stem cell defects in Drosophila and mice upon partial EJC loss.

Conclusions:

• The exon junction complex (EJC) is essential for regeneration in planarians, primarily through its role in maintaining stem and progenitor cell populations.
• The EJC acts as a conserved, posttranscriptional regulator of gene expression within stem cell lineages.
• This study underscores the EJC's critical function in stem cell biology and highlights the value of discovery-based undergraduate research.