GSE123193
The Lin28/let-7 pathway regulates the mammalian caudal body axis elongation program
The heterochronic genes Lin28a/b and let-7 are well-established regulators of invertebrate development, however their functions in patterning the mammalian body plan remain unexplored. In this study, we discovered a novel function of Lin28/let-7 in controlling caudal vertebrae number during body axis formation. We found that FoxD1-driven overexpression of Lin28a or LIN28B led to a striking increase in caudal vertebrae number, whereas loss of Lin28a stunted tail formation. Accordingly, perturbation of the let-7 microRNA family led to the opposite phenotypes. We further show that overexpressing Lin28a in embryos resulted in increased tail bud cell proliferation, whereas Lin28a KO decreased cellular proliferation. This was accompanied by a transcriptional shift, including down-regulation of the neural marker Sox2, and resulted in a pro-mesodermal phenotype with decreased proportions of neural tissue relative to mesoderm in Lin28a-overexpressing embryos. Strikingly, Lin28a KO and let-7 over-expression demonstrated opposite effects, suggesting that the Lin28/let-7 pathway acts upstream of the signaling pathways controlling the self-renewal and cell fate commitment of neuro-mesodermal progenitors. We propose that Lin28a/b activity controls the pool of caudal progenitors during tail development, promotes their self-renewal potential, is involved in controlling the balance of neural versus mesodermal cell fate decisions, and that progressive down-regulation of Lin28a allows for species-specific vertebral formula to be achieved. These findings suggest that Lin28/let-7 play a role in the regulation of tail length through heterochrony of the body plan. Overall design: Study the role of Lin28/let7 pathway in the caudal body axis elongation program