and encode paralogous transcription factors found as a closely linked tandem duplication within holometabolous insects. mutants segment normally, then fail to maintain their segments. Loss of is viable, while loss of both genes results in asegmental larvae.
View Article and Find Full Text PDFBackground: Segmentation in arthropods typically occurs by sequential addition of segments from a posterior growth zone. However, the amount of tissue required for growth and the cell behaviors producing posterior elongation are sparsely documented.
Results: Using precisely staged larvae of the crustacean, , we systematically examine cell division patterns and morphometric changes associated with posterior elongation during segmentation.
We describe the dynamic process of abdominal segment generation in the milkweed bug We present detailed morphological measurements of the growing germband throughout segmentation. Our data are complemented by cell division profiles and expression patterns of key genes, including and as markers for different stages of segment formation. We describe morphological and mechanistic changes in the growth zone and in nascent segments during the generation of individual segments and throughout segmentation, and examine the relative contribution of newly formed versus existing tissue to segment formation.
View Article and Find Full Text PDFVirtually all arthropods all arthropods add their body segments sequentially, one by one in an anterior to posterior progression. That process requires not only segment specification but typically growth and elongation. Here we review the functions of some of the key genes that regulate segmentation: Wnt, caudal, Notch pathway, and pair-rule genes, and discuss what can be inferred about their evolution.
View Article and Find Full Text PDFWnt genes are a family of conserved glycoprotein ligands that play a role in a wide variety of cell and developmental processes, from cell proliferation to axis elongation. There are 13 Wnt subfamilies found among metazoans. Eleven of these appear conserved in arthropods with a pattern of loss during evolution of as many as six subfamilies among hexapods.
View Article and Find Full Text PDFDistal-less (Dll) plays a well-known role in patterning the distal limb in arthropods. However, in some taxa, its expression even during early limb development is not always limited to the distal limb. Here, I trace the expression of Distal-less in a crustacean (Thamnocephalus platyurus) from the early limb bud to later stages of limb development, a period that includes differentiation of juvenile and adult morphology.
View Article and Find Full Text PDFArthropod Struct Dev
March 2007
Setae are a prominent feature of arthropod limbs. In taxa where the limbs develop during the larval phase, developing setae are an integral part of the developing limb bud and their differentiation cannot easily be separated from the early patterning and formation of the overall limb. Here I describe the morphogenesis and adult setae in a branchiopod crustacean, the anostracan, Thamnocephalus platyurus.
View Article and Find Full Text PDFArthropod bodies are formed by a series of appendage-bearing segments, and appendages have diversified both along the body axis within species and between species. Understanding the developmental basis of this variation is essential for addressing questions about the evolutionary diversification of limbs. We examined the development of serially homologous appendages of two insect species, the beetle Tribolium castaneum and the grasshopper Schistocerca americana.
View Article and Find Full Text PDFThe developing leg of Drosophila is initially patterned by subdivision of the leg into proximal and distal domains by the activity of the homeodomain proteins Extradenticle (Exd) and Distal-less (Dll). These early domains of gene expression are postulated to reflect a scenario of limb evolution in which an undifferentiated appendage outgrowth was subdivided into two functional parts, the coxapodite and telopodite. The legs of most arthropods have a more complex morphology than the simple rod-shaped leg of Drosophila.
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