The red egg gene as a novel effective egg color marker for silkworm transgenesis

Ommochromes are major pigments involved in coloration of eggs, eyes, and epidermis of arthropods. The recessive homozygous of egg and eye color mutant of Bombyx mori, red egg (re), exhibits red eggs and dark red eyes instead of normal purplish-brown eggs and black eyes, due to a defect in ommochrome pigment synthesis. The gene responsible for the re mutant is a major facilitator superfamily transporter gene, Bm-re. Here, we demonstrate that the re phenotype can be effectively rescued by an intact Bm-re gene driven by the Bombyx Actin A3 promoter or the baculovirus Immediate Early 1 promoter, indicating that the Bm-re gene can be used as a marker gene for visual screening of transgenic silkworms. The coloration of eggs rescued by the Bm-re transgene could be distinguished from that of host mutant eggs from diapausing period through head pigmentation stage. This allows transgenic screening at earlier embryonic stages and over a longer time period compared to conventional 3xP3 fluorescent markers, without requiring the skill and equipment to detect stemmata fluorescence.

Automated summary

Ommochromes are important pigments involved in the coloration of arthropods. This study focused on the red egg (re) mutant of Bombyx mori, which has red eggs and dark red eyes due to a defect in ommochrome pigment synthesis. The researchers discovered that the Bm-re gene, a major facilitator superfamily transporter gene, can rescue the re phenotype and be used as a marker gene for visual screening of transgenic silkworms. Transgenic screening with the Bm-re gene allows for earlier and longer screening compared to conventional fluorescent markers.