Functional Analysis of the Scarlet Gene in the Cricket Gryllus bimaculatus

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