Hermes (Rbpms) is a Critical Component of RNP Complexes that Sequester Germline RNAs during Oogenesis.

Tristan Aguero,Malgorzata Kloc,Patrick Chang,Yi Zhou,Evelyn Houliston,Mary King

doi:10.3390/jdb4010002

Abstract

The germ cell lineage in Xenopus is specified by the inheritance of germ plasm that assembles within the mitochondrial cloud or Balbiani body in stage I oocytes. Specific RNAs, such as nanos1, localize to the germ plasm. nanos1 has the essential germline function of blocking somatic gene expression and thus preventing Primordial Germ Cell (PGC) loss and sterility. Hermes/Rbpms protein and nanos RNA co-localize within germinal granules, diagnostic electron dense particles found within the germ plasm. Previous work indicates that nanos accumulates within the germ plasm through a diffusion/entrapment mechanism. Here we show that Hermes/Rbpms interacts with nanos through sequence specific RNA localization signals found in the nanos-3′UTR. Importantly, Hermes/Rbpms specifically binds nanos, but not Vg1 RNA in the nucleus of stage I oocytes. In vitro binding data show that Hermes/Rbpms requires additional factors that are present in stage I oocytes in order to bind nanos1. One such factor may be hnRNP I, identified in a yeast-2-hybrid screen as directly interacting with Hermes/Rbpms. We suggest that Hermes/Rbpms functions as part of a RNP complex in the nucleus that facilitates selection of germline RNAs for germ plasm localization. We propose that Hermes/Rbpms is required for nanos RNA to form within the germinal granules and in this way, participates in the germline specific translational repression and sequestration of nanos RNA.

Highlights

Localization of specific RNAs to subcellular domains is one mechanism by which cells restrict protein synthesis in time and space
Our observations show that Hermes/Rbpms is an important component of the nanos RNP particle
We propose that Hermes/Rbpms binds nanos RNA in the nucleus in association with hnRNP I, initiating a series of events that results in nanos but not Vg1 entering the early pathway

Summary

Introduction

Localization of specific RNAs to subcellular domains is one mechanism by which cells restrict protein synthesis in time and space. During Xenopus oogenesis, selected RNAs are localized and retained within the vegetal cortex at two distinct time periods. Most RNAs essential to forming the germline localize very early in oogenesis within a macroscopic structure called the mitochondrial cloud (MC) or Balbiani body [1,2,3,4,5,6,7,8]. One known component of germinal granules is nanos RNA whose product is essential to the preservation of the germline in many diverse species including Drosophila, Xenopus, and mouse [3,13,14,15,16,17,18].

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