Head patterning and Hox gene expression in an onychophoran and its implications for the arthropod head problem

@article{Eriksson2010HeadPA,
  title={Head patterning and Hox gene expression in an onychophoran and its implications for the arthropod head problem},
  author={Bo Joakim Eriksson and Noel Norman Tait and Graham E. Budd and Ralf Janssen and Michael E Akam},
  journal={Development Genes and Evolution},
  year={2010},
  volume={220},
  pages={117-122}
}
The arthropod head problem has puzzled zoologists for more than a century. The head of adult arthropods is a complex structure resulting from the modification, fusion and migration of an uncertain number of segments. In contrast, onychophorans, which are the probable sister group to the arthropods, have a rather simple head comprising three segments that are well defined during development, and give rise to the adult head with three pairs of appendages specialised for sensory and food capture… 

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References

SHOWING 1-10 OF 24 REFERENCES

A conserved mode of head segmentation in arthropods revealed by the expression pattern of Hox genes in a spider.

TLDR
The finding implies that chelicerates, myriapods, crustaceans, and insects share a single mode of head segmentation, reinforcing the argument for a monophyletic origin of the arthropods.

Homology of arthropod anterior appendages revealed by Hox gene expression in a sea spider

TLDR
It is concluded that the protocerebral appendages have been lost in all extant arthropod groups, including the Euchelicerata and the Mandibulata.

The evolution of arthropod heads: reconciling morphological, developmental and palaeontological evidence

TLDR
Current hypotheses about head segmentation and the nature of head structures from various perspectives are reviewed, and the concept of “primary” and “secondary antennae” in Recent and fossil arthropods are developed, it is proposed that Trilobita are stem lineage representatives of the Mandibulata.

Homeotic genes and the arthropod head: expression patterns of the labial, proboscipedia, and Deformed genes in crustaceans and insects.

  • A. AbzhanovT. Kaufman
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 1999
cDNA fragments of the homologues of the Drosophila head homeotic genes labial (lab), proboscipedia (pb), and Deformed (Dfd) have been isolated from the crustacean Porcellio scaber. Because the

The development and evolution of insect mouthparts as revealed by the expression patterns of gnathocephalic genes

TLDR
An atlas of gene expression in the heads of three insects is made: Thermobia domestica and Acheta domestica, which likely exemplify the mandibulate mouthparts present in the common insect ancestor, and Oncopeltus fasciatus, which has piercing–sucking mouth parts that are typical of the Hemiptera.

Hox genes and the evolution of the arthropod body plan 1

TLDR
In this review, the expression and functional data regarding the 10 arthropod Hox genes are summarized and mechanisms of developmental evolutionary change thought to be important for the emergence of novel morphological features within the arthropods are discussed.

The ten Hox genes of the millipede Glomeris marginata

TLDR
The expression patterns of Ultrabithorax and abdominal-A suggest a correlation between the function of these genes and the delayed outgrowth of posterior trunk appendages, indicating that the decoupling of dorsal and ventral segmentation is not restricted to the level of segment polarity genes but apparently includes the Hox genes.

Exploring the myriapod body plan: expression patterns of the ten Hox genes in a centipede.

TLDR
The expression patterns of the Hox genes in the centipede are in many cases intermediate between those of the chelicerates andThose of the insects and crustaceans, consistent with the proposed intermediate phylogenetic position of the Myriapoda.

Evolution of Hox3 and ftz in arthropods: insights from the crustacean Daphnia pulex

TLDR
The results presented here show that Hox3 and ftz have retained a Hox-like expression pattern in crustaceans, in accordance with the proposed model of Hox1, Hox2 and ftZ evolution in arthropods and allows a more precise pinpointing of the loss of ftz “Hox- like behaviour”: in the lineage between the Branchiopoda and the basal insect Thysanura.

Head development in the onychophoran Euperipatoides kanangrensis with particular reference to the central nervous system

TLDR
Evidence is presented to further support the presence of a terminal mouth in the ground plan of the Onychophora and, hence, an acron may not exist in the arthropod clade.