Paternal effects in a wild-type zebrafish implicate a role of sperm-derived small RNAs.

James Ord,Penelope J Watt,Paul R Heath,Alireza Fazeli

doi:10.1111/mec.15505

Abstract

While the importance of maternal effects has long been appreciated, a growing body of evidence now points to the paternal environment having an important influence on offspring phenotype. Indeed, research on rodent models suggests that paternal stress leaves an imprint on the behaviour and physiology of offspring via nongenetic information carried in the spermatozoa; however, fish have been understudied with regard to these sperm-mediated effects. Here, we investigated whether the zebrafish was subjected to heritable influences of paternal stress by exposing males to stressors (conspecific-derived alarm cue, chasing and bright light) before mating and assessing the behavioural and endocrine responses of their offspring, including their behavioural response to conspecific-derived alarm cue. We found that after males are exposed to stress, their larval offspring show weakened responses to stressors. Small RNA sequencing subsequently revealed that the levels of several small noncoding RNAs, including microRNAs, PIWI-interacting RNAs and tRNA-derived small RNAs, were altered in the spermatozoa of stressed fathers, suggesting that stress-induced alterations to the spermatozoal RNA landscape may contribute to shaping offspring phenotype. The work demonstrates that paternal stress should not be overlooked as a source of phenotypic variation and that spermatozoal small RNAs may be important intergenerational messengers in fish.

Highlights

The ancestral environment is already well-established as a factor which can shape the development of offspring phenotypes, and the existence of parental effects is suspected to have a large bearing on the long-term responses of organisms to selective pressures (Räsänen & Kruuk, 2007)
MiRNAs are the most well-known class of small RNA to be implicated in paternal effects, we investigated whether the spermatozoal composition of other small RNA classes was subjected to stress-induced alterations, PIWI-interacting RNAs and tRNA-derived small RNAs
The role of paternal effects has been increasingly studied in the context of paternal investment postfertilization, such as brood pouch influences in seahorses and pipefish (Cunha, Berglund, Mendes, & Monteiro, 2018; Otero-Ferrer et al, 2020), and nest guarding in sticklebacks (Bell et al, 2016; Mcghee & Bell, 2014), paternal effects mediated by alterations to the sperm epigenome have hitherto not been well characterized in nonmammalian vertebrates such as fish

Summary

| INTRODUCTION

The ancestral environment is already well-established as a factor which can shape the development of offspring phenotypes, and the existence of parental effects is suspected to have a large bearing on the long-term responses of organisms to selective pressures (Räsänen & Kruuk, 2007). Rearing environment induces specific changes to salmon sperm DNA methylation which appear to be inherited by the offspring (Rodriguez Barreto et al, 2019), while sperm-mediated paternal effects on phenotype have been demonstrated in zebrafish in response to increased sperm competition It is possible that paternal miRNA and/or other noncoding RNAs delivered in spermatozoa could influence developmental outcomes in fish They could be maladaptive, changes to the RNA consignment or other components of the spermatozoal epigenome could facilitate intergenetational adaptive responses to precondition offspring if necessitated by changes to environmental conditions during the parents’ lifetime (Immler, 2018). We hypothesized that paternal stress could induce measurable influences on stress response physiology and behaviour in the offspring of zebrafish and that such alterations would be linked to alterations in the small RNA composition of the paternal sperm. MiRNAs are the most well-known class of small RNA to be implicated in paternal effects, we investigated whether the spermatozoal composition of other small RNA classes was subjected to stress-induced alterations, PIWI-interacting RNAs (piRNAs) and tRNA-derived small RNAs (tsRNAs)

| METHODS

Findings

| DISCUSSION