Heterodimer of a B chain and an A chain linked by two disulfide bonds. Broadly expressed at a low level throughout the embryo, except the yolk. Expressed at a moderate level in the embryonic midgut. Larval expression is restricted to ten cells of the ventral nerve cord - in four pairs of centrally located cells in the most posterior abdominal segments and in one pair of dorsally located cells in the A1 or A2 segments. Expressed in the embryo and larva. Belongs to the insulin family.