MitosRNAs and extreme anoxia tolerance in embryos of the annual killifish Austrofundulus limnaeus

Claire L Riggs,Steven Cody Woll,Jason E Podrabsky

doi:10.1038/s41598-019-56231-2

Abstract

Embryos of the annual killifish Austrofundulus limnaeus are the most anoxia-tolerant vertebrate. Annual killifish inhabit ephemeral ponds, producing drought and anoxia-tolerant embryos, which allows the species to persist generation after generation. Anoxia tolerance and physiology vary by developmental stage, creating a unique opportunity for comparative study within the species. A recent study of small ncRNA expression in A. limnaeus embryos in response to anoxia and aerobic recovery revealed small ncRNAs with expression patterns that suggest a role in supporting anoxia tolerance. MitosRNAs, small ncRNAs derived from the mitochondrial genome, emerged as an interesting group of these sequences. MitosRNAs derived from mitochondrial tRNAs were differentially expressed in developing embryos and isolated cells exhibiting extreme anoxia tolerance. In this study we focus on expression of mitosRNAs derived from tRNA-cysteine, and their subcellular and organismal localization in order to consider possible function. These tRNA-cys mitosRNAs appear enriched in the mitochondria, particularly near the nucleus, and also appear to be present in the cytoplasm. We provide evidence that mitosRNAs are generated in the mitochondria in response to anoxia, though the precise mechanism of biosynthesis remains unclear. MitosRNAs derived from tRNA-cys localize to numerous tissues, and increase in the anterior brain during anoxia. We hypothesize that these RNAs may play a role in regulating gene expression that supports extreme anoxia tolerance.

Highlights

Embryos of the annual killifish Austrofundulus limnaeus are the most anoxia-tolerant vertebrate
While many miRNAs, the most well-studied class of small ncRNAs, were differentially expressed in response to anoxia and recovery, a very interesting expression signature was identified for mitosRNAs, a class of small ncRNAs derived from the mitochondrial genome[7]
Expressed mitosRNAs are derived from tRNA, rRNA, protein-coding, and non-coding regions of the mitochondrial genome (Fig. 2a, Table 1) and do not reflect proportions of the mitochondrial genome coding for each type of gene (Fig. 2a)

Summary

Introduction

Embryos of the annual killifish Austrofundulus limnaeus are the most anoxia-tolerant vertebrate. MitosRNAs derived from tRNA-cys localize to numerous tissues, and increase in the anterior brain during anoxia We hypothesize that these RNAs may play a role in regulating gene expression that supports extreme anoxia tolerance. A study on small ncRNAs in embryos of A. limnaeus revealed unique expression patterns associated with different anoxia-tolerance phenotypes (i.e. embryonic stages)[7]. MitosRNAs are present in chicken breast muscle, and results suggest they may play a role in muscle growth[15] While these studies indicate that differential expression of mitosRNAs may play a role in growth and development, the study on anoxia tolerant annual killifish was the first to document mitosRNAs, many of which were derived from tRNAs, changing in abundance in response to stress[7]. We focus on these mitosRNAs in annual killifish embryos, which vary in their anoxia-tolerance levels across development

Methods

Results

Conclusion