The dipteran protoracic glands: morphological, genomic and functional studies in the dipteran B. hygida and D. melanogaster

Abstract

Sciarid DNA puff genes are amplified and expressed in a developmentally regulated manner in the salivary gland in response to the increase in ecdysone levels that precede metamorphosis. Data derived from functional studies in the model organism Drosophila melanogaster revealed the existence of cis-regulatory modules that drive gene expression in the salivary gland and the ring gland in the BhC4-1 DNA puff gene promoter region of the sciarid Bradysia hygida. In higher dipterans such as D. melanogaster, the ring gland is the main larval endocrine organ, which is the result of the fusion of the prothoracic glands (responsible for the synthesis of ecdysone), corpora allata (responsible for the synthesis of juvenile hormone) and corpora cardiaca (a neuroendocrine organ). Recent data from our laboratory have shown that the developmentally regulated amplification and transcription of the BhC4-1 DNA puff gene also occurs in the larval prothoracic glands of B. hygida, indicating that this DNA puff gene transcriptional regulatory mechanisms are extensively conserved between drosophilids and sciarids. In addition, these results in B. hygida confirm previous data indicating that the expression DNA puff genes is not restricted to the salivary glands, tissue in which the DNA puffs are formed and reveal that a DNA puff gene can be amplified in two distinct tissues at the same developmental stage. In this context, this project aims to expand the comparative studies between the basal dipteran, B. hygida, and the higher dipteran, D. melanogaster, employing the prothoracic glands of these dipterans as a model. Specifically, the project aims to: a) describe the main embryonic stages of B. hygida and validate the profiles of expression of a set of genes identified in the recently obtained transcriptomes of this embryonic stage (subproject 1); b) to determine the embryonic origin of the B. hygida prothoracic glands and to investigate the profiles of expression of transcription factors that act in the specification of this organ (subproject 1); c) identify amplified domains in the prothoracic glands chromosomes of B. hygida at the time when the DNA puffs are formed in the salivary gland (subproject 2); d) obtain the prothoracic glands transcriptomes of B. hygida at defined ages during the end of the fourth larval instar, developmental time when the DNA puffs are formed in the salivary gland; e) extend in D. melanogaster transgenic lines the characterization of the (-370/-254) cis-regulatory module that represses BhC4-1 expression in the ring gland at developmental times prior to the second larval instar; f) carry out gene interaction experiments in D. melanogaster to identify transcription factors that regulate the BhC4-1 gene in the ring gland. Together, the results obtained in this project will not only contribute to extend the knowledge about dipteran prothoracic glands, but will also contribute with new information in the area of evolutionary developmental biology. (AU)