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

  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},
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… 

Onychophoran Hox genes and the evolution of arthropod Hox gene expression

The spatial expression pattern of the onychophoran Hox genes may contribute to a combinatorial Hox code that is involved in giving each segment its identity, apparently predates the evolution of distinct segmental differences in external morphology seen in arthropods.

Expression of arthropod distal limb-patterning genes in the onychophoran Euperipatoides kanangrensis

This study investigated the expression patterns of six genes known to function during insect distal limb development in the onychophoran Euperipatoides kanangrensis, i.e., clawless, aristaless, spineless, zinc finger homeodomain 2, rotund, and Lim1.

The fate of the onychophoran antenna

Data on early axogenesis in anostracan crustaceans show that even in the earliest embryos, before the antennula and antennal nerves are developed, the circumoral anlagen of the brain display very prominent nerves which run into the frontal filament organ (also known as the cavity receptor organ), which leads to conclude that the frontal filaments are indeed homologous to the primary antenna.

Subdivision of arthropod cap-n-collar expression domains is restricted to Mandibulata

Expression data from two chelicerate outgroup taxa suggest that the signature two-domain head expression pattern of cnc evolved at the base of Mandibulata, and the observation of the archetypal labral and mandibular segment domains in a crustacean exemplar supports the synapomorphic nature of mandibulate cnc expression.

Regressive evolution of the arthropod tritocerebral segment linked to functional divergence of the Hox gene labial

It is shown that in the spider Parasteatoda tepidariorum the labial gene has two functions: one function in head tissue maintenance that is conserved between spiders and insects, and a second function in pedipalp limb promotion and specification, which is only present in spiders.

Controversies Surrounding Segments and Parasegments in Onychophora: Insights from the Expression Patterns of Four “Segment Polarity Genes” in the Peripatopsid Euperipatoides rowelli

The data clearly show that parasegments, even if present, cannot be regarded as the initial metameric units of the onychophoran embryo, because the expression of key genes that define the parasegmental boundaries in arthropods occurs after the segmental boundaries have formed.

Neural Markers Reveal a One-Segmented Head in Tardigrades (Water Bears)

The immunolabelling against serotonin, FMRFamide and α-tubulin reveals that the tardigrade brain is a dorsal, bilaterally symmetric structure that resembles the brain of onychophorans and arthropods rather than a circumoesophageal ring typical of cycloneuralians (nematodes and allies).

Analysis of the Wnt gene repertoire in an onychophoran provides new insights into the evolution of segmentation

Many onychophoran Wnt genes are expressed in segment polarity gene-like patterns, suggesting a general role for these ligands during segment regionalization, as has been described in arthropods.

Theme and Variation in the Development of Insect Mouthparts

The development, specification, and patterning of insect mouthparts, with comparisons to the legs of Drosophila melanogaster are reviewed, and the evolution of serially homologous structures is reflected on.



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

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

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

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

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

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

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.

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

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

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.