A Requirement for ERK-Dependent Dicer Phosphorylation in Coordinating Oocyte-to-Embryo Transition in C. elegans

Abstract

Signaling pathways and small RNAs direct diverse cellular events, but few examples are known of defined signaling pathways directly regulating small RNA biogenesis. We show that ERK phosphorylates Dicer on two conserved residues in its RNAse IIIb and dsRNA-binding domain, and phosphorylation of these residues is necessary and sufficient to trigger Dicer’s nuclear translocation in worms, mice, and human cells. Phosphorylation of Dicer on either site inhibits Dicer function in the female germ line and dampens small RNA repertoire. Our data demonstrate that ERK phosphorylates and inhibits Dicer during meiosis I for oogenesis to proceed normally in C. elegans and that this inhibition is released before fertilization for embryogenesis to proceed normally. The conserved Dicer residues, their phosphorylation by ERK, and the consequences of the resulting modifications implicate an ERK-Dicer nexus as a fundamental component of the oocyte-to-embryo transition and an underlying mechanism coupling extracellular cues to small RNA production.

Functional analysis of microRNA pathway genes in the somatic gonad and germ cells during ovulation in C. elegans

“…These results indicate that miRNAs are required in the mouse somatic gonad for normal fertility. In worms, Dicer/ dcr-1 activity is required in the somatic gonad for fertility (Drake et al, 2014) and Argonaute/ alg-1 acts in the somatic distal tip cell to control germline proliferation (Bukhari et al, 2012). However, the specific events of oocyte maturation and ovulation that require miRNA activity in the somatic gonad cells in worms remain unknown.…”

“…While translational regulation is essential for meiotic maturation in animals (Mendez and Richter, 2001), the activity of miRNAs may not be required for germ cell development in all organisms (Ma et al, 2010). In worms, Dicer is phosphorylated and localized to the nucleus during most of oogenesis in worms, thereby preventing its normal cytoplasmic processing role (Drake et al, 2014). However, miRNA biogenesis likely functions at an early stage of germ cell development because mature, processed miRNAs are present in oocytes (Gu et al, 2009; McEwen et al, 2016).…”

“…It is clear that some maternal miRNAs that are present in oocytes, including the miR-35 family, are essential for early development (Alvarez-Saavedra and Horvitz, 2010). Mosaic analysis indicates that Dicer activity is not essential in the germ line for the processes of oocyte maturation and ovulation to occur (Drake et al, 2014). However, it remains possible that maternal miRNAs act in the oocyte to more finely regulate the processes of oocyte maturation and ovulation.…”

“…Notably, the differences in miRNA abundance between worms that have zygotic deletion of Dicer and wild-type animals were found to be modest (Drake et al, 2014; Grishok et al, 2001, Knight and Bass 2001). This is surprising because Dicer is required for the cytoplasmic processing of miRNAs.…”

DNA Methylation Influences the Expression of DICER-LIKE4 Isoforms, Which Encode Proteins of Alternative Localization and Function

“…Dicer of Schizosaccharomyces pombe, which directs heterochromatin formation, was shown to shuttle between the nucleus and cytoplasm through motifs that mediate nuclear export and retention (Emmerth et al, 2010). Caenorhabditis elegans Dicer can relocalize to the nucleus following ERK-mediated phosphorylation (Drake et al, 2014), while the nematode Trichinella spiralis evolved a Dicer with an N-terminal NLS, which can likely mediate RdDM to repress transposons (Sarkies et al, 2015). Finally, metazoan Dicer is cytoplasmic, but human Dicer encodes a noncanonical nuclear localization signal, normally masked in the folded protein, and was shown to shuttle into the nucleus where it represses spurious interferon response activation (White et al, 2014;Doyle et al, 2013;Burger and Gullerova, 2015).…”