Differential microarray analysis of Drosophila mushroom body transcripts using chemical ablation

Abstract

Mushroom bodies (MBs) are the centers for olfactory associative learning and elementary cognitive functions in the Drosophila brain. As a way to systematically elucidate genes preferentially expressed in MBs, we have analyzed genome-wide alterations in transcript profiles associated with MB ablation by hydroxyurea. We selected 100 genes based on microarray data and examined their expression patterns in the brain by in situ hybridization. Seventy genes were found to be expressed in the posterodorsal cortex, which harbors the MB cell bodies. These genes encode proteins of diverse functions, including transcription, signaling, cell adhesion, channels, and transporters. Moreover, we have examined developmental functions of 40 of the microarray-identified genes by transgenic RNA interference; 8 genes were found to cause mild-to-strong MB defects when suppressed with a MB-Gal4 driver. These results provide important information not only on the repertoire of genes that control MB development but also on the repertoire of neural factors that may have important physiological functions in MB plasticity.hydroxyurea ͉ RNAi ͉ brain development ͉ learning and memory M ushroom bodies (MBs) are the centers for higher-order functions in the Drosophila brain, participating in diverse behaviors such as olfactory associative learning and elementary cognition (1). In the adult brain, MBs consist of Ϸ2,500 neurons per brain hemisphere. The cell bodies of their intrinsic neurons [Kenyon cells (KCs)] are located in the posterodorsal cortex above a prominent dendritic structure called the calyx, which receives olfactory information from the antennal lobes (ALs) via the inner antennocerebral tract. KCs extend axons through the peduncles, which split dorsally into two lobes, ␣ and ␣Ј, and medially into three lobes, ␤, ␤Ј, and ␥ (Fig. 1A). During development, the Drosophila MB neurons originate from four neuroblasts per brain hemisphere (2-5), with each neuroblast giving rise to an indistinguishable set of neurons and glia (6). The adult Drosophila MB comprises three types of axonal projection groups, ␥, ␣Ј͞␤Ј, and ␣͞␤ (7, 8), which are sequentially generated by the division of the MB neuroblasts on the basis of birth order (9). Notably, this structural subdivision is proposed to reflect functional distinctions (10-12). Moreover, consistent with their behavioral functions, many of the genes required for learning and memory are preferentially expressed in MBs (13-15).Intriguingly, studies have revealed that the Drosophila Pax-6 homologs, eyeless (ey) and twin of eyeless, which were originally implicated as master control genes in eye development (16), are expressed in MBs and have important functions in structural differentiation of MB neurons (3,4,17). In particular, ey is expressed in MB neuroblasts and their progeny through development, and mutations in ey disrupt MB neuropil structures. Furthermore, molecular studies have shown that, unlike the feedback mechanism in the eye, ey and toy are independently controlled in MBs, with ey being ...

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