fuss protein expression is mainly observed during embryonic development in the embryonic brain, the developing stomatogastric nervous system, single cells lying anterior to the CNS which will develop into inner gustatory neurons, and the ventral nerve cord. It is expressed post-mitotically and specifically in neuronal cells. fuss protein first appears at embryonic stage 13 and the number of fuss-positive cells increases continuously from early to late embryonic stages. At embryonic stage 16, expression can be observed in two to five cells per hemineuromere with ascending numbers from posterior to anterior. fuss expression partially overlaps with the interneuron marker dac, overlaps with toy expression in one neuron per abdominal hemineuromere and with ap in two ventral interneurons per hemineuromere in the embryonic ventral nerve cord. The fuss positive cells are interneurons. fuss is expressed in a subset of gustatory neurons in larval and adult stages. In larvae, fuss expression is observed in inner gustatory sense organs. It is expressed in two pairs of neurons in the dorsal pharyngeal sensilla, one neuron pair in the dorsal pharyngeal organ, and two neuron pairs in the posterior pharyngeal sensilla. These neurons are associated with bitter sensing and caffeine response. Later in adults, fuss expression continues in gustatory receptor neurons (GRNs) of the proboscis. It is also expressed in two GRNs each in the last two tarsal segments in every leg. Based upon comparison with markers for specific sensilla, fuss is expressed in bitter neurons in S- and I-type sensilla and in salt attracting neurons in L-type sensilla. Targeted DamID experiments to identify genes coexpressed with fuss in adult neurons show that toy, ato, and acj6 are expressed in fuss-positive neurons while ple and Ilp2 are not.