Divergent gene networks select endocrine glands or trachea from a common segmentally repeated precursor in Drosophila

Abstract

The main endocrine organ of Drosophila, the ring gland, is formed by the fusion of the corpora allata (producing Juvenile Hormone), the prothoracic gland (Ecdysone) and the corpus cardiacum (Adipokinetichormone and others). The embryonic origin of the corpus cardiacum from cephalic mesodermal cells has been established, but the origin of the corpora allata (ca) and prothoracic gland (pg) is unknown. We demonstrate that the corpora allata and prothoracic gland develop from cephalic ectodermal cells that in other segments of the body give rise to the trachea. We identify Hox and Vvl as common primary genes required for trachea, corpora allata and prothoracic gland specification; as well as Snail as a specific corpora allata and prothoracic gland gene. Snail controls the ephitelial to mesenchymal transition (EMT) that is one of the major differences between the ring gland and trachea development. We also show that the trachea can be converted into corpora allata or prothoracic gland and viceversa. Our data indicate that endocrine glands and trachea evolved by the divergence of a homologous segmentally repeated structure.