Search results for "engrailed"
showing 10 items of 14 documents
Arrays in rays: terminal addition in echinoderms and its correlation with gene expression
2005
Summary The echinoderms are deuterostomes that superimpose radial symmetry upon bilateral larval morphology. Consequently, they are not the first animals that come to mind when the concepts of segmentation and terminal addition are being discussed. However, it has long been recognized that echinoderms have serial elements along their radii formed in accordance with the ocular plate rule (OPR). The OPR is a special case of terminal growth, forming elements of the ambulacra that define the rays in echinoderms. New elements are added at the terminus of the ray, which may or may not be marked by a calcified element called the terminal plate (the “ocular” of sea urchins). The OPR operates in eve…
Successive specification ofDrosophilaneuroblasts NB 6-4 and NB 7-3 depends on interaction of the segment polarity geneswingless,gooseberryandnaked cu…
2001
The Drosophila central nervous system derives from neural precursor cells, the neuroblasts (NBs), which are born from the neuroectoderm by the process of delamination. Each NB has a unique identity, which is revealed by the production of a characteristic cell lineage and a specific set of molecular markers it expresses. These NBs delaminate at different but reproducible time points during neurogenesis (S1-S5) and it has been shown for early delaminating NBs (S1/S2) that their identities depend on positional information conferred by segment polarity genes and dorsoventral patterning genes. We have studied mechanisms leading to the fate specification of a set of late delaminating neuroblasts,…
Segmental Organization of Cephalic Ganglia in Arthropods
2007
Cephalic ganglia in arthropods encompass neuromeres of the supraesophageal ganglion (i.e., the brain) and the subesophageal ganglion. Whereas neuromeres of the subesophageal ganglion are clearly distinguishable, the segmental pattern of the brain is derived and less well understood. In this article, we give an overview of the current state of a long-lasting debate on the segmental organization of the arthropod head and brain, discussing embryonic morphological and molecular data, with a main focus on insects. Embryonic expression data on key developmental genes such as engrailed, orthodenticle, and Hox genes will be summarized to compare the metameric organization of the head (sub- and supr…
optomotor-blind suppresses instability at the A/P compartment boundary of the Drosophila wing.
2008
Formation and function of the A/P compartment boundary of the Drosophila wing have been studied intensely. The boundary prevents mingling of A and P cells, is characterized by an expression discontinuity of several genes like engrailed, Cubitus interruptus, hedgehog and decapentaplegic and is essential for patterning the wing. Compared with segmental or compartmental boundaries in several other systems which generally manifest as folds or clefts, the wing A/P boundary is morphologically inconspicuous in both the larval and adult stage. We show here that the Drosophila wing A/P boundary, too, is susceptible to fold and cleft formation and that these processes are suppressed by the T-box tran…
Expression of en and wg in the embryonic head and brain of Drosophila indicates a refolded band of seven segment remnants
1992
ABSTRACT Based on the expression pattern of the segment polarity genes engrailed and wingless during the embryonic development of the larval head, we found evidence that the head of Drosophila consists of remnants of seven segments (4 pregnathal and 3 gnathal) all of which contribute cells to neuromeres in the central nervous system. Until completion of germ band retraction, the four pregnathal segment remnants and their corresponding neuromeres become arranged in an S-shape. We discuss published evidence for seven head segments and morphogenetic movements during head formation in various insects (and crustaceans).
Segment polarity and DV patterning gene expression reveals segmental organization of theDrosophilabrain
2003
The insect brain is traditionally subdivided into the trito-, deuto- and protocerebrum. However, both the neuromeric status and the course of the borders between these regions are unclear. The Drosophila embryonic brain develops from the procephalic neurogenic region of the ectoderm, which gives rise to a bilaterally symmetrical array of about 100 neuronal precursor cells, called neuroblasts. Based on a detailed description of the spatiotemporal development of the entire population of embryonic brain neuroblasts, we carried out a comprehensive analysis of the expression of segment polarity genes (engrailed, wingless, hedgehog, gooseberry distal,mirror) and DV patterning genes (muscle segmen…
Homology modeling using simulated annealing of restrained molecular dynamics and conformational search calculations with CONGEN: application in predi…
1997
We have developed an automatic approach for homology modeling using restrained molecular dynamics and simulated annealing procedures, together with conformational search algorithms available in the molecular mechanics program CONGEN (Bruccoleri RE, Karplus M, 1987, Biopolymers 26:137-168). The accuracy of the method is validated by "predicting" structures of two homeodomain proteins with known three-dimensional structures, and then applied to predict the three-dimensional structure of the homeodomain of the murine Msx-1 transcription factor. Regions of the unknown protein structure that are highly homologous to the known template structure are constrained by "homology distance constraints,"…
Analysis of neural elements in head-mutant Drosophila embryos suggests segmental origin of the optic lobes.
1995
We describe the development of 20 sensory organs in the embryonic Drosophila head, which give rise to 7 sensory nerves of the peripheral nervous system (PNS), and 4 ganglia of the stomatogastric nervous system (SNS). Using these neural elements and the optic lobes as well as expression domains of the segment polarity gene engrailed in the wild-type head of Drosophila embryos as markers we examined the phenotype of different mutants which lack various and distinct portions of the embryonic head. In the mutants, distinct neural elements and engrailed expression domains, serving as segmental markers, are deleted. These mutants also affect the optic lobes to various degrees. Our results suggest…
Early steps in building the insect brain: neuroblast formation and segmental patterning in the developing brain of different insect species
2003
In insects, morphological, molecular and genetic studies have provided a detailed insight into the ontogenetic processes that shape the ventral nerve cord. On the other hand, owing to its complexity and less obvious segmental composition, the knowledge about the development of the brain is still fragmentary. A promising approach towards gaining insight into fundamental processes underlying brain development is the comparison of embryonic brain development among different insect species. However, so far such comparative analyses are scarce. In this review, we summarize and compare data on the early steps in brain formation in different hemi- and holometabolous insects. We show that basic asp…
Role of en and novel interactions between msh, ind, and vnd in dorsoventral patterning of the Drosophila brain and ventral nerve cord
2010
AbstractSubdivision of the neuroectoderm into discrete gene expression domains is essential for the correct specification of neural stem cells (neuroblasts) during central nervous system development. Here, we extend our knowledge on dorsoventral (DV) patterning of the Drosophila brain and uncover novel genetic interactions that control expression of the evolutionary conserved homeobox genes ventral nervous system defective (vnd), intermediate neuroblasts defective (ind), and muscle segment homeobox (msh). We show that cross-repression between Ind and Msh stabilizes the border between intermediate and dorsal tritocerebrum and deutocerebrum, and that both transcription factors are competent t…