The role of stem cells in midgut growth and regeneration

The Kanduca sexta (L.) [Lepidoptera: Sphingidae] and Heliothis virescens (F .) [Lepidoptera. Noctuidae] midguts consist of a pseudostratified epitheliu m surrounded by striated muscle and tracheae. This epithelium contains gobl et, columnar, and basal Stem cells. The stem cells are critically important in that they are capable of massive proliferation and differentiation. Thi s growth results in a fourfold enlargement of the midgut at each larval mol t. The stem cells are also responsible for limited cell replacement during repair. While the characteristics of the stem cell population vary over the course of an instar, stem cells collected early in an instar and those col lected late can start in vitro cultures. Cultures of larval stem, goblet, a nd columnar cells survive in vitro for several mc, through proliferation an d differentiation of the stem cells. One of the two polypeptide differentia tion factors which have been identified and characterized from the culture medium has now been shown to be present in midgut in vivo. Thus the ability to examine lepidopteran midgut stem cell growth in vitro and in vivo is pr oving to be effective in determining the basic features of stem cell action and regulation.