Role of abd-A and Abd-B in Development of Abdominal Epithelia Breaks Posterior Prevalence Rule

Abstract

Hox genes that determine anteroposterior body axis formation in all bilaterians are often found to have partially overlapping expression pattern. Since posterior genes dominate over anterior Hox genes in the region of co-expression, the anterior Hox genes are thought to have no function in such regions. In this study we show that two Hox genes have distinct and essential functions in the same cell. In Drosophila, the three Hox genes of the bithorax complex, Ubx, abd-A and Abd-B, show coexpression during embryonic development. Here, we show that in early pupal abdominal epithelia, Ubx does not coexpress with abd-A and Abd-B, while abd-A and Abd-B continue to coexpress in the same nuclei. The abd-A and Abd-B are expressed in both histoblast nest cells and larval epithelial cells of early pupal abdominal epithelia. Further functional studies demonstrate that abd-A is required in histoblast nest cells for their proliferation and suppression of Ubx to prevent first abdominal segment like features in posterior segments while in larval epithelial cells it is required for their elimination. We also observed that these functions of abd-A are required in its exclusive as well as the coexpression domain with that of Abd-B. The expression of Abd-B is required in histoblast nest cells for their identity while it is dispensable in the larval epithelial cells. The higher level of Abd-B in the seventh abdominal segment, that down-regulates abd-A expression, leads this segment to be absent in males or of smaller size in females. We also show that abd-A in histoblast nest cells positively regulates expression of wingless for the formation of the abdominal epithelia. Our study reveals an exception to the rule of posterior prevalence and shows that two different Hox genes have distinct functions in the same cell, which is essential for the development of abdominal epithelia.

Stuxnet Facilitates the Degradation of Polycomb Protein during Development

“…Consistently, we found that increased Pc activity led to disrupted tergite boundary formation ( Figure 2B), a phenotype that is linked with disturbance of homeotic genes (Karch et al, 1985;Breen, 1999;Wang et al, 2013;Singh and Mishra, 2014). When stx 2 somatic clones were induced, a similar tergite boundary defect was observed ( Figures 2C and 2D).…”

DrosophilaHox genes induce melanised pseudo-tumours when misexpressed in hemocytes

“…While overexpression of abd-A shows relatively stronger phenotypes described here, Abd-B overexpression does not. It supports our earlier finding in which we observed a non-homeotic growth promoter role of abd-A during formation of the adult cuticle during pupation, while Abd-B does not show any such role [46].…”

Divergent Connectivity of Homologous Command-like Neurons Mediates Segment-Specific Touch Responses in Drosophila

“…The offspring neurons thus generated selfassemble to form circuit architectures that mediate behaviors. The segmental boundary of anterior and posterior Wave neurons with distinct functional and morphological characteristics (Figure 4C) roughly corresponds to the expression boundary of the Hox gene Abd-B (Singh and Mishra, 2014). In the future, the study of command neurons such as the Wave neuron could inform us on how homologous neurons diverge in structure throughout development, possibly by differential recruitment of receptors for axon/dendrite guidance cues across segments under the regulation of Hox and other spatially restricted transcription factors (Hilliard and Bargmann, 2006;Lu et al, 2009).…”