Kar4 is required for the normal pattern of meiotic gene expression

Area of Science:

• Molecular Biology
• Yeast Genetics
• Epigenetics

Background:

• Kar4p, a yeast homolog of METTL14, is crucial for mRNA N6-methyladenosine (m6A) methylation, regulating meiotic entry.
• Kar4p has a second, non-catalytic function in meiosis, independent of its methylation activity.

Purpose of the Study:

• To investigate the impact of Kar4p loss and subsequent mRNA methylation changes on the early meiotic transcriptome in yeast.
• To elucidate the non-catalytic role of Kar4p in meiosis, particularly its effect on gene expression and protein levels.

Main Methods:

• Microarray analysis and RNA sequencing to assess transcriptomic changes in kar4Δ/Δ mutants.
• Mass spectrometry to identify proteins with altered levels in kar4Δ/Δ mutants.
• Genetic manipulation (overexpression of IME1 and RIM4) to rescue meiotic defects.

Main Results:

• kar4Δ/Δ mutants showed delayed and reduced expression of Ime1p-dependent early genes and Ndt80p-dependent late genes.
• The early gene defect was rescued by IME1 overexpression, while the late gene defect required both IME1 and RIM4 overexpression.
• Mass spectrometry revealed significantly reduced protein levels for meiotic recombination genes, despite normal transcript levels, which were rescued by RIM4 and IME1 co-overexpression.

Conclusions:

• Kar4p's loss affects both mRNA methylation-dependent and independent meiotic processes.
• Kar4p's non-catalytic function likely operates at the translational level, impacting protein production for key meiotic genes.
• These findings provide insights into Kar4p's multifaceted role in regulating yeast meiosis.