Overexpression of LIM Homeodomain Gene Arrowhead Induces Pleiotropic Developmental Alterations in the Silkworm, Bombyx mori.

LIM homeodomain (LIM-HD) is a versatile family of transcription factors that act as master regulators in various developmental processes of eukaryotes, and one of the LIM-HD encoded genes is the arrowhead (AWH). In silkworm Bombyx mori, the Arrowhead gene (BmAWH) functions as a key component activating all three fibroin genes in the silk glands of B. mori, but the potential pleiotropic effects of BmAWH on various tissues of the silkworm is yet to be discovered. The objective of this study is to investigate the functional role of a BmAWH gene in the B. mori (Dazao) developmental process, using the piggyBac-based transgene technique. The size of transgenic line silk glands have become smaller, resulting in the reduction in whole cocoon weight, cocoon shell weight, and cocoon-shell ratio. Overexpression of BmAWH has induced significant changes in juvenile hormone levels in female larvae at the fifth instar larval stage. Female reproductive defects (reduction in fecundity rate, abnormal egg morphology) were observed. In addition, transgenic line larvae exhibit the complete disappearance of larval body patterns and color (melanin pigmentation). Since the LIM-HD protein functions to orchestrate complex developmental programs, this study may shed light on evolutionary adaptations and the divergence of insect gene functions.