TC016194

It has been shown that Bar has two paralogs in Drosophila melanogaster, BarH1 and BarH2 which seem to be functionally redundant. Blast searching shows that this gene duplication event happened after the divergence of D. melanogaster and Tribolium castaneum, meaning that Bar is a 2:1 ortholog from D. melanogaster to T. castaneum. As BarH1 and BarH2 are functionally redundant in flies, the lack of paralogs in T. castaneum make it an attractive alternative model organism to investigate the role of Bar, without the possibility of paralog interactions resulting in skewed or weakened knock down phenotypes. Bar has been shown to be involved in the proper differentiation of the distal leg tips, antennae, sensory hairs, and eyes of D. melanogaster, with the most prominent changes among these being in the eyes (resulting in narrowed bar shapes) and the legs (resulting in unsegmented, clubbed distal leg tips). These two strong effects have been shown to be conserved in T. castaneum, as the knockdown of TcBar resulted in slightly narrowed eyes, and fused tarsal and pre-tarsal leg segments. These results show that Bar may be important for eye and distal leg development in the red flour beetle, and that at least some of the functions of Bar appear to be conserved between D. melanogaster and T. castaneum. However, the other, less well described roles of Bar in D. melanogaster were seemingly absent in the TcBar RNAi individuals. No obvious changes in the number, patterning, or shape of sensory hairs or antennae were observed. This may be due to an overall weaker knockdown phenotype, where even the most obvious changes, such as eye and distal leg differentiation were slight compared to research done in D. melanogaster. This means that although we did not see any evidence for Bar involvement in the development of these structures, we are not confident that this is the case. Further research needs to be done in order to investigate the role of Bar in T. castaneum sensory hairs and antennae, as well as producing a stronger knockdown phenotype with drastically reduced eye width, and completely clubbed distal leg tips to more convincingly show the role of Bar in the eye. If in these drastic individuals no effect is had on the antennae, and the sensory hair prevalence, patterning, and form, are normal, then it can be said that Bar is not important for the development of these structures in T. castaneum. This would mean that these functions were either lost in this line, or gained in D. melanogaster after the split of these two lineages. In addition to investigating these conserved functions, the possibility for diverged function in the flour beetle was possible, as RNAseq data from the Tomoyasu lab showed that there is a significantly higher expression of Bar in the elytra, a structure the fruit fly does not possess. This hinted that Bar may have taken on a new role in the beetle’s elytra. However, knockdown of Bar in T. castaneum was unable to produce any morphological changes in these structures, meaning we were unable to show any evidence for novel functions taken on by the gene in the flour beetle. The presence of a significant Bar expression level in Tribolium elytra may be explained by the relatively high density of sensory hairs on these structures, as it has been shown that Bar is important for sensory hair development in D. melanogaster, although we were unable to show this to be true in T. castaneum.