P2.30 Thursday, Jan. 5 Exploring the Loss of the Hox Gene abdominal-A in the Mite Archegozetes longisetosus BARNETT, A.A.*; THOMAS, R.H.; Southern Illinois University, Carbondale; Southern Illinois University, Carbondale email@example.com
Hox gene products have a highly conserved role throughout Metazoa in patterning the anterior-posterior axis. This high degree of functional conservation makes observations of their losses rare. Sequencing the Hox cluster of the chelicerate mite Archegozetes longisetosus revealed the loss of the posterior patterning Hox gene abdominal-A (abd-A). abd-A has been shown to be necessary in determining the identity of posterior segments in a number of arthropod species, and is often co-expressed with the Hox gene Ultrabithorax (Ubx). In order to explore the potential causes and consequences of the loss of abd-A, we followed the expression of the mite orthologues of Ubx, the segmentation gene engrailed (en), and the Hox co-factor homothorax (hth) in the posterior chelicerate tagma, the opisthosoma. The expression of en in the opisthosoma is absent in early stages, followed by the simultaneous appearance of two stripes. This simultaneous appearance of two segments was confirmed by SEM and by time-lapse photography. No further en expression was observed, indicating a reduction in the segmental nature of the mite opisthosoma. Ubx is expressed in a stable group of cells in the posterior opisthosoma in two groups of cells straddling the proctodael invagination. However, unlike other studied chelicerates, Ubx was not expressed in the genital region. hth expression is dynamic in the opisthosoma, and is initially expressed in the anterior opisthosoma and into the fourth limb buds of the anterior prosoma. However, hth is restricted to the posterior opisthosoma in later developmental stages where it is also expressed in the mesodermal midgut rudiment. These data are preliminary observations that are aiding in our understanding of the evolutionary pressures leading to Hox gene loss.