Submitted to: Molecular Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/14/2003
Publication Date: 7/23/2003
Citation: Loeb, M.J., Clark, E.A., Blackburn, M.B., Hakim, R.S., Elsen, K., Smagghe, G. 2003. Isolation and characterization of microsatellite loci for the entomopathogenic fungus beauveria bassiana (ascomycota: hypocreales). Molecular Ecology. 53:186-198. Interpretive Summary: The midgut is responsible for digesting the food needed to make the caterpillar grow. In order to control insects by affecting the midgut, it is important to know how the growth and repair of the midgut is regulated. We culture stem cells from the midguts of a pest insect, the tobacco budworm, in the laboratory. In past work, we were able to identify four growth factors that induce midgut stem cells to transform to mature cells, as well as another that induces them to multiply. In this work, we incubated stem cells with these growth factors to look at their interactions as they caused stem cells to multiply and to change to mature, working gut cells. We found indications that the receptors for these factors may be not be the same, but the differentiation factors prevent the multiplication factor from working, and to a lesser extent, the multiplication factor inhibits the action of the differentiation factors. In addition, we showed that other growth factors, usually associated with mammals, induce midgut stem cells to change into mature midgut cells characteristic of non-feeding stages of caterpillars, and into cells not usually present in midgut at all. This information can be used in the future by scientists who may be able to introduce these traits into viruses or bacteria, or into plants that the caterpillars eat, to induce the stem cells in the midguts of feeding caterpillars to produce abnormal midgut cells at the next molt and thus inhibit normal gut function as a new method of insect control.
Technical Abstract: Previously, we showed that isolated stem cells from midguts of Heliothis virescens can be induced to multiply in response to a multiplication protein (MP) isolated from pupal fat body, or to differentiate to larval types of mature midgut cells in response to either of 4 differentiation factors (MDFs) isolated from larval midgut cell-conditioned medium or pupal hemolymph. In this work we showed that the receptors for MDF-2 and MP decayed at different time intervals and thus may be different. However, the receptors appeared to be linked, since conditioned medium and MDF-2 prevented the action of MP on stem cells; MP by itself appeared to repress stem cell differentiation. Epidermal growth factor, retinoic acid and platelet-derived growth factor induced isolated midgut stem cells of H. virescens and Lymantria dispar to multiply and to differentiate to mature midgut cells characteristic of prepupal, pupal and adult lepidopteran midgut epithelium, and to squamous-like cells and scales not characteristic of midgut tissue. Midgut stem cells appear to be multipotent and their various differentiated fates can be influenced by several growth factors.