Hox gene Ultrabithorax is required for wing formation in Tribolium (beetles)

By | April 20, 2021
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Do you know that Beetles account for around 25% of all known life-forms on this planet. They belong to the order Coleoptera, which happens to be the largest and most diverse order, not only in the insect class, but in the entire animal kingdom. It is believed that there are eight times as many beetle species as there are fish, amphibian, reptile, bird and mammal species all put together. Eight times!!! Those are really huge numbers of beetles which goes on to tell us that these creatures can survive in any environment.
Like majority of Insects , beetles bodies are divided into three sections: the head, the thorax, and the abdomen. Thorax bears all three pairs of legs , two pairs of wings and region posterior to thorax is all abdomen. Beetles are endopterygotes with complete metamorphosis ( holometabolism).

One feature of Beetles , which is quite distinct from other insects is the presence of hard modified forewings termed as “Elytra”.
With this amount of introduction we will move into today’s classic paper ,which comes from the lab of Robin Denell . Major credit should go to Rob Denell for turning Red flour beetle (Tribolium) into a useful model organism and in this article which published in “Nature” (2005) showing the importance of Hox gene Ultrabithorax (Ubx) in providing membranous identity to wing in the beetle Tribolium castaneum.

Generally insects have two pairs of wing , but during evolution these structures have undergone many morphological changes. The example which comes to mind immediately is the widely studied Dipteran fruit fly Drosophila melanogaster, where the hind wings are modified into balancing organs called “Halteres”. Hox protein Ultrabithorax brings in this change of wing to haltere by repressing various wing patterning genes in haltere imaginal disc. Its interesting to note that in Drosophila , wing develops without any input from Hox proteins. Antennapedia is the only hox protein expressed in disc proper of imaginal disc (Ubx is expressed only in peripodial membrane of wing disc ) and mutations in Antennapedia has no effect on wing formation in Drosophila. However to prove further the input of Hox proteins is only important for formation of morphologically specialized wing derivatives such as halteres, and not the more ancestral wings, we need to examine in other insect orders. This is what exactly Rob Dennel’s lab did in Tribolium (Beetle) belonging to order Coleoptera. Unlike Drosophila which is a Dipteran where hind wings are modified to halteres, Beetles are infact opposite in this regard. In beetles, such as Tribolium castaneum, it is the forewings that are modified (to form elytra), while the hindwings retain a morphologically more ancestral identity.

Read how Ubx specifies wing identity in PART-II

1) Ultrabithorax is required for membranous wing identity in the beetle Tribolium castaneum.
Tomoyasu Y, Wheeler SR, Denell RE.
Nature. 2005 Feb 10;433(7026):643-7.

2) Homeotic genes and the regulation and evolution of insect wing number.
Carroll SB, Weatherbee SD, Langeland JA.
Nature. 1995 May 4;375(6526):58-61.