Introduction—embryology and Phylogeny

Anderson, D. T.

doi:10.1016/b978-0-08-017069-5.50006-8

Cited by 82 publications

(114 citation statements)

References 23 publications

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“…Our morphological data on neurogenesis in E. kanangrensis are in line with recent publications on neurogenesis in other onychophoran species that describe the segregation of single neural precursors from the ventral neuroectoderm (24)(25)(26). In the basal position, the neural precursors divide to generate smaller intermediate precursors.…”

Section: Do the Neural Characters Of Onychophorans Support The Myriocsupporting

confidence: 74%

“…During early embryogenesis in E. kanangrensis, the mouth and the anus furrow form, and subsequently the germ band becomes distinct. The two halves of the germ band become separated by presumptive extraembryonic tissue, and bilateral segmental swellings with intersegmental groves become visible, which appear in an anterior-to-posterior sequence (26,33,34). The sequential formation of segments correlates with an anterior-to-posterior gradient of development, which facilitates the analysis of the sequence of developmental processes.…”

Section: Resultsmentioning

confidence: 99%

“…Although the phylogenetic position of onychophorans is still debated, many phylogenies group them with euarthropods and possibly tardigrades in the phylum Arthropoda; thus onychophorans share a common ancestor with euarthropods (8,(19)(20)(21)(22)(23). Analyses of neurogenesis in onychophorans suggests that, similar to insects and crustaceans, single neural precursors are formed in the neuroectoderm, rather than groups of cells as seen in chelicerates and myriapods (24)(25)(26). This suggests that the nervous system of the last common ancestor of arthropods was generated by the segregation of single neural precursor cells and thus the formation of single neuroblasts in insects and crustaceans would represent an ancestral character of neurogenesis.…”

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confidence: 99%

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Expression patterns of neural genes in Euperipatoides kanangrensis suggest divergent evolution of onychophoran and euarthropod neurogenesis

Eriksson

Stollewerk

2010

Proc. Natl. Acad. Sci. U.S.A.

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One of the controversial debates on euarthropod relationships centers on the question as to whether insects, crustaceans, and myriapods (Mandibulata) share a common ancestor or whether myriapods group with the chelicerates (Myriochelata). The debate was stimulated recently by studies in chelicerates and myriapods that show that neural precursor groups (NPGs) segregate from the neuroectoderm generating the nervous system, whereas in insects and crustaceans the nervous tissue is produced by stem cells. Do the shared neural characters of myriapods and chelicerates represent derived characters that support the Myriochelata grouping? Or do they rather reflect the ancestral pattern? Analyses of neurogenesis in a group closely related to euarthropods, the onychophorans, show that, similar to insects and crustaceans, single neural precursors are formed in the neuroectoderm, potentially supporting the Myriochelata hypothesis. Here we show that the nature and the selection of onychophoran neural precursors are distinct from euarthropods. The onychophoran nervous system is generated by the massive irregular segregation of single neural precursors, contrasting with the limited number and stereotyped arrangement of NPGs/stem cells in euarthropods. Furthermore, neural genes do not show the spatiotemporal pattern that sets up the precise position of neural precursors as in euarthropods. We conclude that neurogenesis in onychophorans largely does not reflect the ancestral pattern of euarthropod neurogenesis, but shows a mixture of derived characters and ancestral characters that have been modified in the euarthropod lineage. Based on these data and additional evidence, we suggest an evolutionary sequence of arthropod neurogenesis that is in line with the Mandibulata hypothesis.achaete-scute homologue | euarthropod phylogeny | Notch signaling

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Section: Do the Neural Characters Of Onychophorans Support The Myriocsupporting

confidence: 74%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Expression patterns of neural genes in Euperipatoides kanangrensis suggest divergent evolution of onychophoran and euarthropod neurogenesis

Eriksson

Stollewerk

2010

Proc. Natl. Acad. Sci. U.S.A.

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“…The origin and phylogenetic position of the Trilobita were not decided, but she rejected the possibility of their ancestry to the Crustacea and Chelicerata. The di-and probably triphyletic nature of the phylum was strongly supported by Anderson (16), who compared the developmental morphology of the three living groups and concluded that the arthropods lack the common developmental theme that unites other morphologically diverse phyla. These arguments were so convincingly articulated that they have begun to appear in modern textbooks (17 (4), on the basis of a broad-comparison of the internal organ systems, and Boudreaux (19), who attempted to show that some 17 both "derived" (as opposed to primitive) and shared characters are not results of convergent evolution.…”

Section: Discussionmentioning

confidence: 78%

Centipedal hemocyanin: its structure and its implications for arthropod phylogeny.

Mangum¹,

Scott²,

Black³

et al. 1985

Proc. Natl. Acad. Sci. U.S.A.

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The oxygen carrier hemocyanin occurs in the blood of Scutigera coleoptrata, a uniramous arthropod, as well as the crustaceans and chelicerates. The native polymer appears to be composed ofsubstructures having the same size and electron-dense image as those of other arthropod hemocyanins but assembled into a unique multiple and arranged in a unique configuration. The simplest explanation of these fridings is that the arthropod hemocyanins have a common origin, exemplifying a derived (as opposed to primitive) character shared by each of the three living groups.In contrast to the hemoglobins (Hbs), the hemocyanins (Hcs) are regarded as coherent in taxonomic distribution. They are found in only two groups: the molluscs, in three of the four classes examined, and the arthropods, in the crustaceans and chelicerates. Also unlike the Hbs, the Hcs are always widespread in a particular taxon. Therefore, the report by Rajulu (1) of a Hc-like substance in a single order of uniramous arthropods, the scutigeromorph centipedes, is somewhat surprising. All but a few of the Uniramia lack an 02 carrier in the blood, the exceptions containing Hb rather than Hc. The brief report (1) was based on high levels of blood Cu and N, the blue color of the blood, and its absorption peak at 340 nm, all of which resemble features of the chelicerates. He did not, however, present the decisive evidence-namely, reversible 02 binding. Later, when the amino acid composition of this protein proved to differ from that of a crustacean Hc, he identified it with less certainty (2). Not unexpectedly, his inference is treated tentatively in a recent volume on centipede biology (3). Moreover, the possibility ofHc in the Uniramia appears to be either unknown to or dismissed by proponents of various points of view in the current debate on arthropod phylogeny (4,5).Our findings show that the common house centipede Scutigera coleoptrata (Linnaeus) does contain a Hc that resembles the crustacean and chelicerate Hcs in fundamental structural features but differs in superficial respects. The molecule is of both structural and phylogenetic interest. METHODS AND MATERIALSBlood, which does not clot, was withdrawn into a glass capillary from the pericardial cavity. With the exception of the samples used for electron microscopy, the blood was of necessity frozen and stored until the volume sufficient for a particular measurement accumulated.Activities of the inorganic ions in the blood were measured with ion-selective electrodes (6). Absorption of the native blood (in physiological saline) and the Hc subunits (in 10 mM EDTA at pH 8.95) was examined with a Beckman recording spectrophotometer. 02 binding was determined by the cell respiration method (6), using a miniaturized respirometer that accepts samples as small as 300 1ul.The Hc was purified on a 1 x 20 cm column of Sephacryl S-300 equilibrated with Tris buffer (0.1 ionic strength, pH 7.65) containing 50 mM MgCl2 (buffer A). Most of the Hc eluted in the void volume.Whole blood was electrophoresed on poly...

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“…The vast majority of arthropods elongate from a posterior region, the so-called growth zone 23,24 . As the name implies, elongation in the growth zone has been traditionally assumed to be due to high rates of cell division in the posterior [25][26][27][28] . However, other cellular behaviours-cell migration, cell rearrangements, cell shape change-could be used singly or in combination [29][30][31][32][33][34] .…”

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confidence: 99%

Changing cell behaviours during beetle embryogenesis correlates with slowing of segmentation

Nakamoto

Hester²,

Constantinou

et al. 2015

Nat Commun

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Segmented animals are found in major clades as phylogenetically distant as vertebrates and arthropods. Typically, segments form sequentially in what has been thought to be a regular process, relying on a segmentation clock to pattern budding segments and posterior mitosis to generate axial elongation. Here we show that segmentation in Tribolium has phases of variable periodicity during which segments are added at different rates. Furthermore, elongation during a period of rapid posterior segment addition is driven by high rates of cell rearrangement, demonstrated by differential fates of marked anterior and posterior blastoderm cells. A computational model of this period successfully reproduces elongation through cell rearrangement in the absence of cell division. Unlike current models of steady-state sequential segmentation and elongation from a proliferative growth zone, our results indicate that cell behaviours are dynamic and variable, corresponding to differences in segmentation rate and giving rise to morphologically distinct regions of the embryo.

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Introduction—embryology and Phylogeny

Cited by 82 publications

References 23 publications

Expression patterns of neural genes in Euperipatoides kanangrensis suggest divergent evolution of onychophoran and euarthropod neurogenesis

Expression patterns of neural genes in Euperipatoides kanangrensis suggest divergent evolution of onychophoran and euarthropod neurogenesis

Centipedal hemocyanin: its structure and its implications for arthropod phylogeny.

Changing cell behaviours during beetle embryogenesis correlates with slowing of segmentation

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