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Hox and tale requirement to select endocrine vs trachea from a common segmentally repeated ectodermal precursor

AuthorsSánchez-Higueras, Carlos ; Sotillos, Sol ; Castelli-Gair Hombría, James
KeywordsSymposium on Hox and TALE transcription factors in Development and disease. Cost. European Cooperation in Science and Technology
Issue Date2012
CitationSymposium on HOX and TALE Transcription Factors in Development and Disease (2012)
AbstractSegmented organisms present serially repeated homologous structures along the antero-posterior body axis. During development, Hox proteins and their cofactors control the segmental specialization of these structures transforming their morphology and function. Despite this divergence, the structures can still be clearly identified as homologous elements. Here we present evidence showing a situation of extreme divergence where the original ectodermal structure has evolved into completely different structures: in one case, two mesenchymal endocrine components of the ring gland; and in the other, the internal epithelial respiratory tracheal network. The tracheal tree of Drosophila is a segmentally repeated epithelial organ. It develops from the invagination of ten ectodermal placodes present from the second thoracic to the eighth abdominal segments. These placodes express two main tracheal regulators: the trachealess (trh) and the ventral veinless (vvl) genes. The segmental vvl expression is not restricted to the tracheal placodes but is present in patches of cells at homologous positions in other segments. We show that two of these patches in the cephalic region also form placodes that invaginate but do not give rise to trachea. We found that the placode on the maxillary segment is the primordium of the corpora allata and the one on the labium is the primordium of the prothoracic gland, which are two of the most important insect endocrine organs. We also observe that these endocrine organs transform into trachea when besides Vvl they express Trh indicating that they are homologous structures. Vvl expression is necessary for the formation of these endocrine organs and the correct development of the trachea. The activation of vvl in both the gland and the tracheal placodes is under the regulation of Hox proteins. Deformed is required for vvl expression in the corpora allata, Sex combs reduced in the prothoracic gland, and the central Hox genes for vvl expression in the tracheal placodes. The development of trachea and endocrine organs initiates with the invagination of the polarized epithelial cells. The morphological divergence occurs shortly after invagination, when activation of Snail in the endocrine primordia induces an epithelial to mesenchymal transition. This is followed by the coalescence of the corpora allata and prothoracic gland primordia that migrate dorsally fusing, first, to the corpora cardiaca and, later, to the contralateral primordium in what becomes the ring gland. Our data are important because: (1) they uncover the genetic and developmental mechanisms for ring gland morphogenesis and (2) indicate that the respiratory tracheal organs and two main endocrine glands arose through a process of divergent evolution from an ectodermal repeated structure that lead to extremely different morphological and functional organs.
DescriptionResumen del trabajo presentado al Symposium on HOX and TALE Transcription Factors in Development and Disease, celebrado en San Lorenzo de El Escorial, Madrid (España) del 28 de noviembre al 1 de diciembre de 2012.
Appears in Collections:(CABD) Comunicaciones congresos
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