Differential dominance of an allele of the Drosophila tbetah gene challenges standard genetic techniques

The biogenic amine octopamine (OA) and its precursor tyramine (TA) are involved in controlling a plethora of different physiological and behavioral processes. The tyramine-{beta}-hydroxylase (t{beta}h) gene encodes the enzyme catalyzing the last synthesis step from TA to OA. Here, we report differential dominance (from recessive to overdominant) of the putative null t{beta}hnM18 allele in two behavioral measures in Buridans paradigm (walking speed and stripe deviation) and a proboscis extension assay in the fruit fly Drosophila melanogaster. The behavioral analysis of transgenic t{beta}h expression experiments in mutant and wild type flies as well as of OA- and TA-receptor mutants revealed a complex interaction of both aminergic systems. Our analysis suggests that the different neuronal networks responsible for the three phenotypes show differential sensitivity to t{beta}h gene expression levels. The evidence suggests that this sensitivity is brought about by a TA/OA opponent system modulating the involved neuronal circuits. This conclusion entails important implications for standard transgenic techniques, commonly used in functional genetics.