Immunohistochemical detection of a putative insect cytokine, midgut differentiation factor 1 (MDF-1) in midgut columnar cells of Heliothis virescens

摘要

Two peptides, midgut differentiation factors 1 and 2 (MDF-1 and 2), were previously isolated from conditioned medium in which Manduca sexta midgut cells were grown. They are identical to two portions of the terminal sequence of the protein, fetuin,a prenatal vertebrate liver product. In cultures of Lepidopteran midgut, the MDFs act as cytokines or growth factors by inducing midgut stem cells to differentiate to mature columnar, goblet, endocrine, or nerve-like cells. A polyclonal rabbit antiserumto one of these peptides, MDF-1, was used in this study to stain cultured cells from midguts of 4th instar larvae of the Lepidopteran, Heliothis virescens. Paraffin sections of midgut taken from newly molted, mid- 4th instars, and pre-molting 4th instarlarvae were also stained with the antibody. Intense positive immunostain was observed in basal areas of the cultured columnar cells and in basal lateral areas of columnar cells in the sections of midinstar and premolt 4th instar midgut. Other cell typesdid not interact with the antibody to MDF-1. Few newly molted larval midgut cells were immunopositive, and those that reacted were faintly stained. Mid-last instar columnar cells stained more intensely, and pre-molt columnar cells stained most intenselyof all. Columnar cells from H. virescens appear to sequester and/or produce an MDF-1-like peptide, both in vitro and in vivo, in addition to their other tasks of nutrient intake, digestion, and transport of digested nutrients.