Abstract
Appendages are external projections of the body that serve the animal for locomotion, feeding, or environment exploration. The appendages of the fruit fly Drosophila melanogaster are derived from the imaginal discs, epithelial sac-like structures specified in the embryo that grow and pattern during larva development. In the last decades, genetic and developmental studies in the fruit fly have provided extensive knowledge regarding the mechanisms that direct the formation of the appendages. Importantly, many of the signaling pathways and patterning genes identified and characterized in Drosophila have similar functions during vertebrate appendage development. In this review, we will summarize the genetic and molecular mechanisms that lead to the specification of appendage primordia in the embryo and their posterior patterning during imaginal disc development. The identification of the regulatory logic underlying appendage specification in Drosophila suggests that the evolutionary origin of the insect wing is, in part, related to the development of ventral appendages.
Highlights
Arthropods are the most successful group of animals and represent approximately three-quarters of the animal species currently living on Earth [1]
The function of signaling pathways such as hedgehog (Hh), decapentaplegic (Dpp), Wingless (Wg), Epidermal Growth Factor Receptor (EGFR) and Notch, and the transcription factors Distal-less (Dll), Homothorax (Hth) and members of the Sp family (Btd/Sp1) is fundamental in the formation of appendages. These signaling pathways and transcription factors are linked in regulatory networks, and cooperate to subdivide the developing appendages in different domains of gene expression
In contrast to the dorsal primordia (DP), where distinction between trunk and appendage occurs later in imaginal development, the VP is organized in gene expression domains that subdivide the primordia in different territories (Figure 1C) [16,56,57,58]
Summary
Arthropods are the most successful group of animals and represent approximately three-quarters of the animal species currently living on Earth [1]. Arthropod appendages show great variation in number, shape, and function, allowing multiple purposes from locomotion to feeding or environment sensing Besides their morphological disparity, it is likely that all appendages share common generative rules. While thoracic imaginal precursors (wing, haltere, and legs) originate from a single embryonic segment [8,9], the genital disc primordia is a sexually dimorphic compound primordia derived from three abdominal segments (A8, A9, and A10) (reviewed in [10]). The function of signaling pathways such as hedgehog (Hh), decapentaplegic (Dpp), Wingless (Wg), Epidermal Growth Factor Receptor (EGFR) and Notch, and the transcription factors Distal-less (Dll), Homothorax (Hth) and members of the Sp family (Btd/Sp1) is fundamental in the formation of appendages These signaling pathways and transcription factors are linked in regulatory networks, and cooperate to subdivide the developing appendages in different domains of gene expression. We discuss the regulatory logic behind appendage specification and patterning, and the implications in the evolutionary origin of the insect wing
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