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Chelicerate

Chelicerate

Ubx abd-A

Onychophora

Figure 5.2

Shifts in the anterior boundary of Ubx gene expression in arthropods

Onychophora

Figure 5.2

Shifts in the anterior boundary of Ubx gene expression in arthropods

The expression domains of Ubx (blue) and abd-A (purple) proteins are shown below the body plans of different arthropod groups and onychophora. The anterior boundary of Ubx expression is located in a different segmental position in each group. In each case, this boundary marks a morphological transition in segmental and appendage identity. Diagonal blue and purple stripes in the myriapod and the onychophora indicate the sum of the domains of Ubx and abd-A expression. Segment identities: A, abdominal; G, genital; Mx, maxillary; L, leg; Lab, labial; Op, opisthosomal; T, thoracic; Tr, trunk.

shown that Ubx regulates the distinct segmental identities of T3 and A1. In particular, the Ubx gene represses leg development in A1 and is responsible for the morphological differences between the wing and the haltere (see Chapter 3). An anterior boundary of Ubx expression in T3 is characteristic of all insects, reflecting the conserved insect body plan.

The anterior boundary of Ubx gene expression, however, lies at a different segmental position within the trunks of crustaceans, myriapods, chelicerates, and onychophora (Fig. 5.2). For example, the expression pattern of Ubx in a primitive crustacean lineage, the brine

Ubx abd-A

Brachiopod: Artemia

Brachiopod: Artemia

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