# BmSV2A and BmSV2B Are Involved in Regulating GABAergic Neuron-Related Gene Expression in the Silkworm, Bombyx mori

## TL;DR

This study identifies two genes, BmSV2A and BmSV2B, that regulate GABAergic neuron activity and influence the number of life cycles in silkworms.

## Contribution

The study discovers the role of BmSV2A and BmSV2B in modulating GABAergic neuron-related gene expression to control silkworm voltinism.

## Key findings

- BmSV2A and BmSV2B are located in the V locus and are linked to silkworm voltinism.
- CRISPR/Cas9 editing confirmed that these genes affect GABAergic neuron signal pathway gene expression.
- The GABAergic pathway modulates diapause and life cycle variation in silkworms.

## Abstract

This study reveals the genetic basis of silkworm voltinism. Based on our research findings, we have conclusively demonstrated that the GABAergic neuron signal pathway is pivotal in regulating silkworm voltinism. Thereafter, population genetic analysis was conducted on SNP variations in 109 silkworm strains using silkworm pan-genome datasets and classical genetic mapping of V genes (the main gene controlling voltinism). We identified four candidate genes related to silkworm voltinism. Using CRISPR/Cas9-mediated gene editing technology, we verified that the two genes, BmSV2A and BmSV2B, may participate in voltinism control by regulating gene expression in the GABAergic neuron signal pathway. Our research provides a new perspective for revealing the genetic basis of silkworm voltinism.

In insects, the number of life cycles varies inter- and intra-specifically, and it is widely accepted that the variation in the number of life cycles is an adaptive response to diverse environmental conditions. However, the molecular mechanism that underlies the variety and plasticity in the number of life cycles is largely unknown. In the silkworm, Bombyx mori, the Voltinism (V) locus has three alleles, V1(univoltine; dominant), V2 (bivoltine; standard), and V3 (polyvoltine; recessive), which are known to generate variation in the number of life cycles in a year under natural conditions, with obligatory diapause for the V1 allele, facultative diapause for V2, and non-diapause for V3. Here, we further confirm that the γ-aminobutyric acid (GABA)ergic neuron signal pathway modulates progeny diapause via controlling diapause hormone release. A population genetic analysis (Fst) revealed that the synaptic vesicle glycoprotein 2A and 2B (BmSV2A and BmSV2B) genes, tightly related to the transport of neurotransmitters, are located in the V locus. Importantly, using the CRISPR/Cas9 editing technique, we have discovered that the BmSV2A and BmSV2B genes increased or modified the expression of GABAergic neuron signal pathway genes, respectively. These results demonstrate that BmSV2A and BmSV2B, positioned within the V locus, could be involved in voltinism control via the GABAergic neuron signal pathway.