Functional exploration of the Sex combs reduced gene in Gryllus bimaculatus

The Hox gene Sex combs reduced (Scr) is recognized as a key factor in the development of the head and thorax in insects. However, its function in the growth, development and morphogenesis of Gryllus bimaculatus remains poorly understood. This study aimed to explore the function of the Scr gene in G. bimaculatus by using CRISPR/Cas9 technology to generate an Scr gene knock-out strain. Intercrossing the G₀ generation knock-out individuals with wild-type individuals yielded the G₁ generation to screen the mutant strain. It was found that the knock-out of the Scr gene had a severe impact on the growth and development of G. bimaculatus, resulting in high mortality and making it difficult to obtain Scr^-/- mutants. Therefore, heterozygous individuals (Scr^+/-) with 1 bp deleted were obtained for investigation. The results showed that the Scr deletion led to ectopic segment formation in the G₀ generation. In the G₂ generation, it was observed that stable Scr^-/- strains displayed abnormal embryonic development, characterized by enlarged, blackened and lethal eggs during embryogenesis. During the post-embryonic stage, Scr^-/- mutants exhibited abnormalities in body segmentation, particularly in the head-thorax region, resulting in a dorsal ridge structure. Furthermore, some Scr^+/- individuals exhibited a dorsal ridge during the nymphal stage. Notably, this characteristic did not persist into the adult stage. Our findings highlight the distinct but crucial roles of the Scr gene in both embryonic and post-embryonic growth and development of G. bimaculatus.