Hox genes in Insects – Isolation of Hox genes from 6 different Insect orders
Hox proteins provide positional cues along the anterior posterior axis in majority of animals on this planet. This positional information is crucial in segment specific morphogenesis. Hox proteins is a part of antennapedia class of proteins, which consists of about 100 genes in bilaterians , divided into 30 gene families belonging to four major groups: HOX / PARAHOX genes (45 genes, four gene families), HOX-related genes (nine genes, five gene families), NK genes (16 genes, seven gene families), and NK-related genes (28 genes, 18 pseudogenes, 14 gene families).
These genes belonging to Antennapedia class, played significant role in understanding animal radiation by providing valuable insights in to phylogenetic pattern and genetic pathways in animal development. Hox genes grabbed more attention in evodevo studies as they are crucial for segment specific identities along the AP axis in embryo. Hox genes were first discovered in fruitfly Drosophila melanogaster and subsequently found in all bilaterians. Hox like genes were isolated from Cnidarians and placozoans, making presence of Hox or Hox like genes in all animals (except sponges and Ctenophora ).
The importance of insects lies in the fact that they happen to be most diverse animals on this planet In fact there are more species of insects than there are all other species put together. Despite the important status of insects in animal tree of life and Hox class of proteins in evo devo studies not much is known about Hox genes in different orders of Insects.
In a new study by Hadrys H, et al., Published in Plos one journal reported isolation of new Hox gene sequences from different orders of insects. These 37 new partial homeobox sequences of Hox cluster genes (lab, pb, Hox3, ftz, Antp, Scr, abd-a, Abd-B, Dfd, and Ubx) from six different insect orders, the apterygote Diplura and Archaeognatha, and the pterygote orders Ephemeroptera, Odonata, Plecoptera, and Dermaptera, which are crucial to insect phylogenetics.
The main goal of our study was to add as many new Hox cluster gene sequences from phylogenetically particularly important insect orders to the database as possible.These new gene sequences provide an excellent resource and forms first step towards comparative Hox gene studies in insects. In other words, the new data provide a starting point for phylogenetic and developmental studies investigating the apterygote-pterygote (wingless to wing) transition.
Before this publication , Hox genes have been isolated from only 8 out of some 35 insect orders. The full content of Antennapedia genes has so far only been reported for Folsomia candida, Tribolium castaneum and Drosophila melanogaster. The important thing to know is that all the information related to antennapedia class of proteins sequences was coming from only two orders, the Hymenoptera and the Diptera and for any evodevo question, a data from wide array of sequences belonging to different orders is required.
Studies on model systems offered tremendous insights into the genetic principles of bilaterian development. However for current EvoDevo research we require data from non-model animal systems, since most of the established model systems are phylogenetically quite derived.
If one wants to understand the origin of winged insects, we require data of hox genes (especially scr, antp and Ubx hox genes are linked to wing development in Drosphila) from the basal group of insects which lacked wings and also from orders of insects which displayed wings for the first time, to perform comparative studies .
For this very purpose the authors specially looked into more details for Hox genes in order odonata as recent molecular phylogenetic analyses suggest a basal position for Odonata within the Pterygota , making odonates place vital in origin of wings in insects . They managed to isolate all 8 Hox genes for odonates as well as the homeotic gene Hox3 (bicoid). This information related to Hox genes coming from basal winged insects becomes indispensable for comparative studies to unravel the origin and evolution of wings in Insects.
Citation: Hadrys H, Simon S, Kaune B, Schmitt O, Schöner A, et al. (2012) Isolation of Hox Cluster Genes from Insects Reveals an Accelerated Sequence Evolution Rate. PLoS ONE 7(6): e34682. doi:10.1371/journal.pone.0034682 (1040)