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- Janssen, Ralf, et al.
(författare)
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Gene expression suggests decoupled dorsal and ventral segmentation in the millipede Glomeris marginata (Myriapoda: Diplopoda)
- 2004
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Ingår i: Developmental Biology. - : Elsevier BV. - 0012-1606 .- 1095-564X. ; 268:1, s. 89-104
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Tidskriftsartikel (refereegranskat)abstract
- Diplopods (millipedes) are known for their irregular body segmentation. Most importantly, the number of dorsal segmental cuticular plates (tergites) does not match the number of ventral structures (e.g., sternites). Controversial theories exist to explain the origin of this so-called diplosegmentation. We have studied the embryology of a representative diplopod, Glomeris marginata, and have analyzed the segmentation genes engrailed (en), hedgehog (hh), cubitus-interruptus (ci), and wingless (wg). We show that dorsal segments can be distinguished from ventral segments. They differ not only in number and developmental history, but also in gene expression patterns. engrailed, hedgehog, and cubitus-interruptus are expressed in both ventral and dorsal segments, but at different intrasegmental locations, whereas wingless is expressed only in the ventral segments, but not in the dorsal segments. Ventrally, the patterns are similar to what has been described from Drosophila and other arthropods, consistent with a conserved role of these genes in establishing parasegment boundaries. On the dorsal side, however, the gene expression patterns are different and inconsistent with a role in boundary formation between segments, but they suggest that these genes might function to establish the tergite borders. Our data suggest a profound and rather complete decoupling of dorsal and ventral segmentation leading to the dorsoventral discrepancies in the number of segmental elements. Based on gene expression, we propose a model that may resolve the hitherto controversial issue of the correlation between dorsal tergites and ventral leg pairs in basal diplopods (e.g., Glomeris) and is suggestive also for derived, ring-forming diplopods (e.g., Juliformia).
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| 2. |
- Prpic, Nikola-Michael, et al.
(författare)
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Gene expression in spider appendages reveals reversal of exd/hth spatial specificity, altered leg gap gene dynamics, and suggests divergent distal morphogen signaling
- 2003
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Ingår i: Developmental Biology. - 0012-1606 .- 1095-564X. ; , s. 119-140
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Tidskriftsartikel (refereegranskat)abstract
- Leg development in Drosophila has been studied in much detail. However, Drosophila limbs form in the larva as imaginal discs and not during embryogenesis as in most other arthropods. Here, we analyze appendage genes in the spider Cupiennius salei and the beetle Tribolium castaneum. Differences in decapentaplegic (dpp) expression suggest a different mode of distal morphogen signaling suitable for the specific geometry of growing limb buds. Also, expression of the proximal genes homothorax (hth) and extradenticle (exd) is significantly altered: in the spider, exd is restricted to the proximal leg and hth expression extends distally, while in insects, exd is expressed in the entire leg and hth is restricted to proximal parts. This reversal of spatial specificity demonstrates an evolutionary shift, which is nevertheless compatible with a conserved role of this gene pair as instructor of proximal fate. Different expression dynamics of dachshund and Distal-less point to modifications in the regulation of the leg gap gene system. We comment on the significance of this finding for attempts to homologize leg segments in different arthropod classes. Comparison of the expression profiles of H15 and optomotor-blind to the Drosophila patterns suggests modifications also in the dorsal—ventral patterning system of the legs. Together, our results suggest alterations in many components of the leg developmental system, namely proximal—distal and dorsal—ventral patterning, and leg segmentation. Thus, the leg developmental system exhibits a propensity to evolutionary change, which probably forms the basis for the impressive diversity of arthropod leg morphologies.
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