The
let-7 miRNA regulates developmental timing in C. elegans and is an important paradigm for investigations of miRNA functions in mammalian development. We have examined the role of miRNA precursor processing in the temporal control and lineage specificity of the
let-7 miRNA. In situ hybridization (ISH) in E9.5 mouse embryos revealed early induction of
let-7 in the developing central nervous system. The expression pattern of three
let-7 family members closely resembled that of the brain-enriched miRNAs
mir-124,
mir-125 and
mir-128. Comparison of primary, precursor, and mature
let-7 RNA levels during both embryonic brain development and neural differentiation of embryonic stem cells and embryocarcinoma (EC) cells suggest post-transcriptional regulation of
let-7 accumulation. Reflecting these results,
let-7 sensor constructs were strongly down-regulated during neural differentiation of EC cells and displayed lineage specificity in primary cells. Neural differentiation of EC cells was accompanied by an increase in
let-7 precursor processing activity in vitro. Furthermore, undifferentiated and differentiated cells contained distinct precursor RNA binding complexes. A neuron-enhanced binding complex was shown by antibody challenge to contain the miRNA pathway proteins Argonaute1 and FMRP. Developmental regulation of the processing pathway correlates with differential localization of the proteins Argonaute, FMRP, MOV10, and TNRC6B in self-renewing stem cells and neurons.--Wulczyn, F. G., Smirnova, L., Rybak, A., Brandt, C., Kwidzinski, E., Ninnemann, O., Strehle, M., Seiler, A., Schumacher, S., Nitsch, R. Post-transcriptional regulation of the
let-7 microRNA during neural cell specification.