Antibodies were used to examine the expression patterns of Antennapedia (Antp), Ultrabithorax (Ubx), Ubx and abdominal-A combined (Ubx/abd-A), and Distalless (Dll) in the embryos of the moth Manduca sexta. We found that the spatial and temporal pattern of Antp expression in Manduca was correlated with the anterior migration of two patches of epithelium that include the anterior-most tracheal pits, and with the development of functional spiracles. Ubx expression showed an intricate pattern which suggests complex regulation during development. Throughout Manduca embryogenesis the expression of Ubx/Abd-A and Dll was similar to that reported for other insects. However, there was no apparent reduction in Ubx/Abd-A expression in the Manduca abdominal proleg primordia that expressed Dll. The expression of these four proteins was also examined in embryos of the Manduca homozygous homeotic mutant Octopod (Octo). The Octo mutation results in the transformation of A1 and A2 in the anterior direction, with homeotic legs appearing on A1 and occasionally A2. Our results suggest that in Octo animals there is a reduction in the level of Ubx protein expression throughout its domain. Based on homeotic gene expression in wild-type and mutant Manduca and in other insects, we discuss potential roles of homeotic genes in insect morphological evolution.

With the onset of metamorphosis, the abdominal muscles of the moth, Manduca sexta, follow one of three developmental fates: maintenance, respecification, or death. The maintained muscles retain their larval size and morphology throughout adult development. The respecified and dying muscles dedifferentiate, which involves regression, nuclear degeneration, and myofibril breakdown. Nuclei in both dying and respecified muscles also proliferate. The amount of nuclear degeneration is greater in the dying muscle fibers, and the amount of nuclear proliferation is greater in the respecified muscles. Four to ten days after pupation, the sizes of the respecified muscles stabilize while the dying muscles are lost. During regression, a subset of the respecified muscle fibers die. The surviving respecified muscle fibers grow and differentiate during the last half of adult development. In respecified muscles, denervation triggers an increased amount of nuclear degeneration and a decreased amount of nuclear proliferation. As a result, denervated respecified fibers experience increased muscle regression including an increased loss of muscle fibers and sometimes muscle death. Surviving respecified fibers still grow and differentiate yet are only 5 to 12% of the control size. Denervation triggers dedifferentiation in maintained muscles, resulting in fiber loss and occasionally muscle death. The percentage of fibers which dedifferentiate varies between different muscles. Denervation also triggers nuclear proliferation, with the amount of nuclear proliferation correlated with the extent of dedifferentiation of the individual muscle fibers. The dedifferentiated maintained fibers subsequently undergo differentiation in the absence of muscle growth.

Over the last years, there has been great success in driving stem cells toward insulin-expressing cells. However, the protocols developed to date have some limitations, such as low reliability and low insulin production. The most successful protocols used for generation of insulin-producing cells from stem cells mimic in vitro pancreatic organogenesis by directing the stem cells through stages that resemble several pancreatic developmental stages. Islet cell fate is coordinated by a complex network of inductive signals and regulatory transcription factors that, in a combinatorial way, determine pancreatic organ specification, differentiation, growth, and lineage. Together, these signals and factors direct the progression from multipotent progenitor cells to mature pancreatic cells. Later in development and adult life, several of these factors also contribute to maintain the differentiated phenotype of islet cells. A detailed understanding of the processes that operate in the pancreas during embryogenesis will help us to develop a suitable source of cells for diabetes therapy. In this chapter, we will discuss the main transcription factors involved in pancreas specification and beta-cell formation.