A recent paper by Nelson and Ambros [1] reports that let-7 heterochronic microRNA is absent in Caenorhabditis species of the japonica group. Research in C. elegans has shown that let-7 plays an essential role during larval to adult transition and mutations in let-7 cause lethality. Authors used one species of the japonica group, C. sulstoni, to further investigate microRNA gene regulatory network. The results revealed that the loss of let-7 function in this species is compensated by other let-7 family members, i.e., miR-48, miR- 84, and miR-241.

Considering that let-7 is highly conserved across bilaterians [2], the results presented in this paper are exciting. However, more work is needed to understand the basis of such an evolutionary change and other potential changes in microRNA-mediated processes.

Reference:
1. Nelson C. and Ambros V. (2021). A cohort of Caenorhabditis species lacking the highly conserved let-7 microRNA. G3, 11(3), jkab022. DOI: 10.1093/g3journal/jkab022.

2. Pasquinelli A.E. et al. (2000). Conservation of the sequence and temporal expression of let-7 heterochronic regulatory RNA. Nature. 408:86–89.