Expression profiles of lncRNAs, miRNAs, and mRNAs and interaction analysis indicate their potential involvement during testicular fusion in Spodoptera litura

Testicular fusion of Spodoptera litura occures during metamorphosis, which benefits sperms development. Previous research identified involvement of ECM-integrin interaction pathways, MMPs in testicular fusion, but the regulatory mechanism remains unclear. RNA-seq was performed to analyze long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) in testes, aiming to uncover potential regulatory mechanisms of testicular fusion. 2150 lncRNAs, 2742 targeted mRNAs, and 347 miRNAs were identified in testes at three different developmental stages. Up-regulated DElncRNAs and DEmRNAs, as well as down-regulated DEmiRNAs, were observed during testicular fusion, while the opposite expression pattern was observed after fusion. Enrichment analysis of DEmRNAs revealed that cAMP signal pathway, ECM remodeling enzymes, ECM-integrin interaction pathways, and cell adhesion molecules were potentially associated with testicular fusion. The identified DElncRNA-DEmiRNA-DEmRNA regulatory network related to cAMP signal pathway, ECM remodeling enzymes suggests their roles during testicular fusion. Our research will provide new targets for studying the mechanism of testicular fusion.

Testes morphology and the identification of transcripts of the hormonal pathways of the velvetbean caterpillar Anticarsia gemmatalis Hübner, 1818 (Lepidoptera: Erebidae)

Anticarsia gemmatalis is one of the main defoliating pests of soybeans in Brazil. In the current study, we characterized the histomorphology of the testes and the spermatogenesis process in A. gemmatalis. We also identified transcripts involved in the biosynthesis, metabolism, and signaling of juvenile and ecdysteroid hormones, in order to provide information about potential mechanisms of regulation of hormonal pathways in this species. Our analyses revealed that the A. gemmatalis larvae have a pair of kidney-shaped testicles. These are divided into four testicular follicles, where there are germ cell cysts at different stages of development. In the pupal stage, the testicles are fused, so adults have a single spherical testis, with a variable number of follicles. The A. gemmatalis has centripetal spermatogenesis and exhibits spermatic dimorphism. We identified 31 transcripts that encode proteins involved in juvenile hormone and ecdysteroid pathways, such as mevalonate kinase, CYP14A1, ecdysone receptor, among others. Our results on the morphology of the testes and spermatogenesis process, as well as identification of the genes involved in hormonal pathways in A. gemmatalis, provide important data for understanding the biology of this agricultural pest, which can be used as a basis for further research in other economically important lepidopterans.

Transcriptomic analysis of the testicular fusion in Spodoptera litura

Background

Lepidoptera is one group of the largest plant-feeding insects and Spodoptera litura (Lepidoptera: Noctuidae) is one of the most serious agricultural pests in Asia countries. An interesting and unique phenomenon for gonad development of Lepidoptera is the testicular fusion. Two separated testes fused into a single one during the larva-to-pupa metamorphosis, which is believed to contribute to sperm production and the prevalence in field. To study the molecular mechanism of the testicular fusion, RNA sequencing (RNA-seq) experiments of the testes from 4-day-old sixth instar larvae (L6D4) (before fusion), 6-day-old sixth instar larvae (L6D6, prepupae) (on fusing) and 4-day-old pupae (P4D) (after fusion) of S. litura were performed.

Results

RNA-seq data of the testes showed that totally 12,339 transcripts were expressed at L6D4, L6D6 and P4D stages. A large number of differentially expressed genes (DEGs) were up-regulated from L6D4 to L6D6, and then more genes were down-regulated from L6D6 to P4D. The DEGs mainly belongs to the genes related to the 20E signal transduction pathway, transcription factors, chitin metabolism related enzymes, the families of cytoskeleton proteins, extracellular matrix (ECM) components, ECM-related protein, its receptor integrins and ECM-remodeling enzymes. The expression levels of these genes that were up-regulated significantly during the testicular fusion were verified by qRT-PCR. The matrix metalloproteinases (MMPs) were found to be the main enzymes related to the ECM degradation and contribute to the testicular fusion. The testis was not able to fuse if MMPs inhibitor GM6001 was injected into the 5th abdomen region at L6D6 early stage.

Conclusions

The transcriptome and DEGs analysis of the testes at L6D4, L6D6 and P4D stages provided genes expression information related to the testicular fusion in S. litura. These results indicated that cytoskeleton proteins, ECM-integrin interaction genes and ECM-related proteins were involved in cell migration, adhesion and fusion during the testicular fusion. The ECM degradation enzymes MMPs probably play a critical role in the fusion of testis.