Functional Analysis of the Scarlet Gene in the Cricket Gryllus bimaculatus

The scarlet gene encodes an ATP-binding cassette transporter involved in eye pigmentation across various insect species. In this study, we functionally characterized the scarlet homolog (Gbst) in the cricket Gryllus bimaculatus, a hemimetabolous model organism. Clustered regularly interspaced short palindromic repeats/CRISPR-associated nuclease 9-mediated knockout of Gbst generated a stable yellow-eyed mutant line (Gbst^−/−) with changed pigmentation evident from embryogenesis through adulthood. Quantitative real-time PCR analysis showed that scarlet expression was extremely low in Gbst^−/−, and the transcript levels of white and brown were also reduced. Histological sections of the compound eyes showed that both WT and Gbst^−/− mutant possessed complete and well-defined ommatidial structures, indicating that the scarlet gene does not affect compound eye structure. In addition, reproduction tests showed that knockout of the Gbst gene did not affect egg production or embryonic viability. These findings demonstrate that Gbst is a key factor involved in eye pigmentation in G. bimaculatus, and has potential for application as a visual transgenic marker gene.