Lepidopteran midgut stem cells in culture: a new tool for cell biology and physiological studies

Holometabolous insects recruit a wide array of stem cell types to fulfil the growth of larval organs at moulting and their remodelling at metamorphosis, thus achieving the final body organization of the adult. Over the years a large number of different stem cells, with specific roles in growth and renewal of insect tissues, have been identified in Lepidoptera and Diptera. A particular interest for the stem cells residing within the insect gut is now emerging and the early morphological studies that analyzed the behaviour of these cells are progressively supported by new cellular and molecular data. After a brief summary of the current knowledge on insect intestinal stem cells, here we will focus on some characteristics of the stem cells in culture of the larval midgut of Bombyx mori. These cells can be released from the midgut just before the fourth moult and, once placed in an appropriate medium, they multiply and differentiate in mature cells that are able to perform normal absorptive and digestive functions in vitro. Thereafter we will discuss the use of this reliable in vitro system as a tool to study intestinal morphogenesis and differentiation, to investigate the specific roles and reciprocal relationships of autophagy and apoptosis during midgut remodelling, and to analyze physiological functions of midgut cells, such as their ability to internalize different substrates and the mechanisms involved. Studies on midgut stem cells appear of key importance in consideration of the extensive similarities evidenced among mammalian and insect intestinal epithelia in their development, organization and molecular regulatory mechanisms.