# Developmental Expression Patterns of miRNA in Mythimna separata Walker (Lepidotera: Noctuidae)

## TL;DR

This study identifies miRNA expression patterns during the development of the oriental armyworm, revealing how these small RNAs regulate genes across life stages.

## Contribution

The study discovers 360 novel miRNAs and their dynamic expression profiles in the pest insect Mythimna separata.

## Key findings

- 400 miRNAs were identified, including 360 novel ones, with distinct expression patterns across developmental stages.
- 75 miRNAs were significantly more abundant in eggs compared to other stages, suggesting key roles in early development.
- Differential miRNA expression in adults indicates a shift in regulatory activity compared to earlier life stages.

## Abstract

Background/Objectives: miRNAs are a family of single-stranded non-coding RNAs that regulate gene expression by targeting messenger RNAs (mRNAs) for suppression, with an average length of 22 nt. The oriental armyworm, Mythimna separata Walker, is a pest insect with long-distance migratory capability, which causes severe loss of grains and pastures in Eastern Asia, Southeastern Asia, and Oceania. This study aims to elucidate the post-transcriptional regulatory mechanisms of miRNAs in the development of this pest. Methods: We carried out small RNA sequencing on samples from eggs, third instar larvae, pre-pupae, pupae, and adults. Results: A total of 400 miRNAs were identified, among which 40 were known and 360 were novel miRNAs. Dynamic trend analysis of miRNAs revealed that 199 miRNAs were highly expressed in eggs (profile 12), while 173 miRNAs were highly expressed in both eggs and pupae (profile 13). The results of differential expression analysis of miRNAs (DEmiR) revealed that 75 miRNAs were significantly more abundant in eggs compared to other developmental stages. Furthermore, more up-regulated miRNAs were observed than down-regulated miRNAs in adults relative to 3rd instar larvae, pre-pupae, and pupae. The core genes for miRNA biosynthesis—Pasha, Dicer1, and Ago1—were highly expressed in eggs but poorly expressed in 3rd instar larvae. KEGG enrichment analyses indicated that several genes in the pentose and glucuronate interconversion pathway, as well as the fructose and mannose metabolism pathway, were regulated by DEmiRs. Conclusions: DEmiRNAs targeted most genes of M. separata, resulting in a complex miRNA–mRNA regulation mode.