A large number of long noncoding RNAs (lncRNAs) are found in many organisms and are play important roles in a variety of biological phenomena, including genomic imprinting, dosage compensation, carcinogenesis and developmental processes　Interestingly, mouse and human microarray analysis revealed that many lncRNA are specifically expressed in nervous system, implying that lncRNAs are the integral parts of neural complexity. In previous studies, we have uncovered dozens of long ncRNA candidates in Drosophila and found that some of them  are expressed in the central nervous system(Inagaki et al., 2005), similar to the case in mice and humans. Here we show that Lobe-less (LOL) RNA is essential for mushroom body morphogenesis and involved in chromatin mediated gene regulation.    LOL RNA was detected in nuclei of neuronal progenitor cell (neuroblast) expressing Caster, a temporal identity factor of neuroblasts.  To elucidate the function of LOL RNA, we established a small deletion strain that lacks the whole transcribed region of LOL RNA.  lol mutant flies showed malformation of the vertical lobes of adult and larval mushroom body.  DNA microarray analysis of mutant and wild type adult head revealed that expression of more than 2,000 genes were significantly affected by lol mutation.   Since genomic loci of lol target genes show statistically evident tendencies to form gene clusters, we investigated genetic interaction between lol and chromatin-mediated transcription.  Polycomb phenotypes of Pc-G mutant males were enhanced by the presence of the lol mutations, and gain-of-function allelesof Antennapedia showed severer phenotypes of antenna-to-leg transformation with higher penetrance.  Taken together, our results indicate that Lobe-less RNA is a new member of Pc-G and essential for mushroom body development.  Current study provides the first evidence that long noncoding RNA contributes in establishment of integrative neural circuits in the brain.