DROSHA but not DICER is required for human haematopoietic stem cell function.

Area of Science:

• Molecular Biology
• Stem Cell Biology
• Gene Regulation

Background:

• DROSHA and DICER are key in microRNA (miRNA) biogenesis.
• DROSHA also cleaves messenger RNAs (mRNAs) independently of miRNAs, crucial for murine hematopoietic stem cell (HSC) pluripotency.
• This involves cleaving specific mRNAs like Myl9 and Todr1 in mice.

Purpose of the Study:

• To investigate if DROSHA's miRNA-independent mRNA cleavage function is conserved in human HSCs.
• To determine the role of DROSHA in maintaining human HSC pluripotency and function.

Main Methods:

• Short hairpin RNAs were used to knock down DROSHA and DICER in human CD34+ HSCs.
• HSC function was assessed in vitro and in humanized mouse models.
• mRNA cleavage was analyzed using capture of 5' phosphorylated RNAs.

Main Results:

• DROSHA knockdown, but not DICER knockdown, impaired human HSC differentiation and engraftment.
• DROSHA was confirmed to cleave MYL9 mRNA in human HSCs, leading to its accumulation upon DROSHA deficiency.
• Ectopic MYL9 expression did not affect human HSC function, and a Todr1 homolog was not identified.

Conclusions:

• A miRNA-independent function of DROSHA is essential for human HSC pluripotency.
• DROSHA directly degrades specific mRNAs in human HSCs.
• MYL9 mRNA degradation alone is insufficient to explain DROSHA's role, indicating other targets or functions are critical.