Carbonell, A. | Search bioRxiv

bioRxiv2020

In response to Li et al.: Linker histones function in Drosophila embryogenesis

In an earlier paper (Perez-Montero et al., 2013), we reported that the embryonic linker histone of Drosophila dBigH1 was essential for early Drosophila embryogenesis since embryos homozygous for the bigH1100 mutation showed strong defects and did not survive beyond zygotic genome activation (ZGA) at cellularization. Recent results challenge these observations since null bigH1 mutations generated by CRISPR/Cas9 methodology turn out to be homozygous viable, as reported in Li et al. (2019) and here. In this regard, Li et al. described a novel mechanism by which lack of dBigH1 is compensated by the early expression of maternal dH1. Here, we confirm this observation and show that such compensatory mechanism is not activated in bigH1100 embryos.

molecular biology↗

bioRxiv2019

In vivo mRNA structure regulates miRNA cleavage in Arabidopsis

MicroRNA (miRNA)-mediated cleavage is involved in numerous essential cellular pathways. miRNAs recognize target RNAs via sequence complementarity. In addition to complementarity, in vitro and in silico studies have suggested that RNA structure may influence the accessibility of mRNAs to miRNA-Induced Silencing Complexes (miRISCs), thereby affecting RNA silencing. However, the regulatory mechanism of mRNA structure in miRNA cleavage remains elusive. Here, we investigated the role of in vivo RNA secondary structure in miRNA cleavage by developing the new CAP-STRUCTURE-seq method to capture the intact mRNA structurome in Arabidopsis thaliana. This approach revealed that miRNA target sites were not structurally accessible for miRISC binding prior to cleavage in vivo. Instead, the unfolding of the target site structure is the primary determinant for miRISC activity in vivo. Notably, we found that the single-strandedness of the two nucleotides immediately downstream of the target site, named Target Adjacent structure Motif (TAM), can promote miRNA cleavage but not miRNA binding, thus decoupling target site binding from cleavage. Our findings demonstrate that mRNA structure in vivo can regulate miRNA cleavage, providing evidence of mRNA structure-dependent regulation of biological processes.

molecular biology↗