Hox Gene Expression of (Channel Catfish) Barbels
Tyler Watson
Department of Biology
Faculty Supervisor: Karen Crow
Barbels are paired sensory structures that occur in multiple disparate lineages of ray-finned fishes that arose multiple times independently. Barbels vary in number, are adorned with taste buds, and are distributed around the jaws, lips or head. Like fins/limbs, barbels consist of an epidermal layer with a mesodermal core, with vascular, muscular, and neural tissues. However, they are highly variable in composition. For example, paddlefish and catfish barbels have a cartilaginous core that stains with Alcian Blue, while zebrafish have a “central rod” that is an acellular, non-mineralized matrix composed of collagen. Hawkins (2008) argued that barbels meet criteria for novelty and asked if they arose by co-option of the Hox fin/limb gene regulatory network (GRN), in the channel catfish (Ictalurus punctatus), based on expression patterns of HoxA13b and HoxD11a. They found no evidence of patterning by these two Hox genes. In paddlefish barbel, we also found no expression of HoxA13 (Archambeault et al. 2014), however we did find expressions of HoxA11, HoxD12 and HoxD13. These genes are not expressed during barbel development in zebrafish-a close relative of catfish (Ostariophysi). But zebrafish barbels also lack a cartilaginous core which is present in both paddlefish and catfish. It is currently unknown whether catfish barbels are patterned by HoxA11/D12/D13 because they weren’t evaluated in Hawkins (2008), but if they are it would warrant reconsideration of the idea that barbels are patterned by co-option of the Hox fin/limb GRN, and support the argument for deep homology of paired, distally elongated vertebrate structures.