Heterodimer of a B chain and an A chain linked by two disulfide bonds. Expressed at a high level in the embryonic mesoderm, with expression continuing after gastrulation and reducing from stage 12 onwards. Highly expressed in the embryonic anterior midgut rudiment and larval midgut. Expressed in the embryo (beginning at the blastoderm stage), and in the larva. Belongs to the insulin family.