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

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, V(1)(univoltine; dominant), V(2) (bivoltine; standard), and V(3) (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 V(1) allele, facultative diapause for V(2), and non-diapause for V(3). 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.