Growth and mitogenic effects of arylphorin in vivo and in vitro

In insects, developmental responses are organ- and tissue-specific. In previous studies of insect midgut cells in primary tissue cultures, growth-promoting and differentiation factors were identified from the growth media, hemolymph, and fat body. Recently, it was determined that the mitogenic effect of a Manduca sexta fat body extract on midgut stem cells of Heliothis virescens was due to the presence of monomeric alpha-arylphorin. Here we report that in primary midgut cell cultures, this some arylphorin stimulates stem cell proliferation in the lepidopterans M. sexta and Spodoptera littoralis, and in the beetle Leptinotarso decemlineata. Studies using S. littorolis cells confirm that the mitogenic effect is due to free alpha-arylphorm subunits. In addition, feeding artificial diets containing arylphorin increased the growth rates of several insect species. When tested against continuous cell lines, including some with midgut and fat body origins, arylphorin had no effect; however, a cell line derived from Lymentria dispar fat body grew more rapidly in medium containing a chymotryptic digest of arylphorin.