m⁶A modulates haematopoietic stem and progenitor cell specification.

Area of Science:

• Epigenetics and RNA Biology
• Developmental Biology
• Hematopoiesis

Background:

• N6-methyladenosine (m6A) is the most prevalent mRNA modification in eukaryotes, yet its role in vertebrate embryogenesis is largely unknown.
• High-throughput sequencing technologies have advanced understanding of m6A functions.
• The endothelial-to-haematopoietic transition (EHT) is critical for generating the first haematopoietic stem/progenitor cells (HSPCs).

Purpose of the Study:

• To investigate the function of m6A modification in vertebrate embryogenesis, specifically during the EHT.
• To elucidate the molecular mechanisms by which m6A regulates the specification of early HSPCs.

Main Methods:

• Utilized m6A-specific methylated RNA immunoprecipitation with high-throughput sequencing (MeRIP-seq) and m6A individual-nucleotide-resolution cross-linking and immunoprecipitation with sequencing (miCLIP-seq) in zebrafish embryos.
• Generated mettl3-deficient zebrafish embryos to assess the impact of reduced m6A levels.
• Performed gene knockdown experiments in mouse models.

Main Results:

• Characterized conserved features of the zebrafish m6A methylome, with peaks near stop codons and an RRACH motif.
• Demonstrated that mettl3 deficiency significantly reduces m6A levels and blocks HSPC emergence in zebrafish.
• Identified that impaired YTHDF2-mediated decay of notch1a and rhoca mRNA in mettl3-deficient embryos leads to sustained Notch signaling, inhibiting EHT and HSPC generation.
• Observed similar phenotypes in Mettl3-knockdown mice.

Conclusions:

• m6A modification is essential for determining cell fate during EHT and specifying early HSPCs in vertebrate embryogenesis.
• The mettl3-m6A pathway regulates HSPC generation by controlling mRNA decay and Notch signaling during EHT.
• These findings highlight the conserved and critical role of m6A in regulating hematopoiesis during vertebrate development.