The let-7 microRNA directs vulval development through a single target.

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• The let-7 microRNA (miRNA) family plays a vital role in regulating stemness across diverse animal species, including humans.
• Mutations in let-7 in C. elegans lead to a severe vulval rupturing phenotype, the underlying cause of which has been unclear.
• It was hypothesized that miRNAs regulate multiple targets, and let-7's role in vulval integrity might stem from the coordinated dysregulation of several genes, or specifically the overexpression of LET-60/RAS.

Purpose of the Study:

• To investigate the specific molecular mechanisms by which let-7 microRNA (miRNA) ensures vulval integrity in C. elegans.
• To determine which let-7 targets are essential for preventing the vulval rupturing phenotype observed in let-7 mutants.
• To elucidate whether let-7 functions by broadly reducing gene expression noise or by regulating specific targets.

Main Methods:

• Utilized CRISPR-Cas9 gene editing technology to modify endogenous let-7 target sites within the C. elegans genome.
• Analyzed the vulval integrity and developmental phenotypes of C. elegans strains with edited let-7 target sites.
• Assessed the necessity and sufficiency of individual let-7 target regulation in preventing vulval rupturing.

Main Results:

• Demonstrated that let-7 functions within the vulval-uterine system to maintain vulval integrity.
• Found that the regulation of most let-7 targets, including the key gene LET-60/RAS, is dispensable for preventing vulval rupturing.
• Identified that the regulation of LIN-41/TRIM71 alone is both necessary and sufficient to prevent the vulval rupturing phenotype.

Conclusions:

• let-7's critical role in preventing vulval rupturing in C. elegans is achieved through the specific regulation of LIN-41/TRIM71.
• The function of let-7 in this context is not to broadly reduce gene expression noise.
• let-7 directs vulval development and integrity via the extensive regulation of a single, defined target, LIN-41/TRIM71.