Kirsten Hildebrandt1, Dieter Kolb1, Christine Klöppel1, Petra Kaspar1,2, Fabienne Wittling1,3, Olga Hartwig1,3, Jannic Federspiel1, India Findji1, Uwe Walldorf4. 1. Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany. 2. Present address: COS Heidelberg, University of Heidelberg, Im Neuenheimer Feld 230, 69120, Heidelberg, Germany. 3. Present address: Hemholtz Institute for Pharmaceutical Research Saarland (HIPS), Saarland University, Building E8.1, 66123, Saarbrücken, Germany. 4. Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany. uwe.walldorf@uks.eu.
Abstract
BACKGROUND: The homeobox gene homeobrain (hbn) is located in the 57B region together with two other homeobox genes, Drosophila Retinal homeobox (DRx) and orthopedia (otp). All three genes encode transcription factors with important functions in brain development. Hbn mutants are embryonic lethal and characterized by a reduction in the anterior protocerebrum, including the mushroom bodies, and a loss of the supraoesophageal brain commissure. RESULTS: In this study we conducted a detailed expression analysis of Hbn in later developmental stages. In the larval brain, Hbn is expressed in all type II lineages and the optic lobes, including the medulla and lobula plug. The gene is expressed in the cortex of the medulla and the lobula rim in the adult brain. We generated a new hbnKOGal4 enhancer trap strain by reintegrating Gal4 in the hbn locus through gene targeting, which reflects the complete hbn expression during development. Eight different enhancer-Gal4 strains covering 12 kb upstream of hbn, the two large introns and 5 kb downstream of the gene, were established and hbn expression was investigated. We characterized several enhancers that drive expression in specific areas of the brain throughout development, from embryo to the adulthood. Finally, we generated deletions of four of these enhancer regions through gene targeting and analysed their effects on the expression and function of hbn. CONCLUSION: The complex expression of Hbn in the developing brain is regulated by several specific enhancers within the hbn locus. Each enhancer fragment drives hbn expression in several specific cell lineages, and with largely overlapping patterns, suggesting the presence of shadow enhancers and enhancer redundancy. Specific enhancer deletion strains generated by gene targeting display developmental defects in the brain. This analysis opens an avenue for a deeper analysis of hbn regulatory elements in the future.
BACKGROUND: The homeobox gene homeobrain (hbn) is located in the 57B region together with two other homeobox genes, Drosophila Retinal homeobox (DRx) and orthopedia (otp). All three genes encode transcription factors with important functions in brain development. Hbn mutants are embryonic lethal and characterized by a reduction in the anterior protocerebrum, including the mushroom bodies, and a loss of the supraoesophageal brain commissure. RESULTS: In this study we conducted a detailed expression analysis of Hbn in later developmental stages. In the larval brain, Hbn is expressed in all type II lineages and the optic lobes, including the medulla and lobula plug. The gene is expressed in the cortex of the medulla and the lobula rim in the adult brain. We generated a new hbnKOGal4 enhancer trap strain by reintegrating Gal4 in the hbn locus through gene targeting, which reflects the complete hbn expression during development. Eight different enhancer-Gal4 strains covering 12 kb upstream of hbn, the two large introns and 5 kb downstream of the gene, were established and hbn expression was investigated. We characterized several enhancers that drive expression in specific areas of the brain throughout development, from embryo to the adulthood. Finally, we generated deletions of four of these enhancer regions through gene targeting and analysed their effects on the expression and function of hbn. CONCLUSION: The complex expression of Hbn in the developing brain is regulated by several specific enhancers within the hbn locus. Each enhancer fragment drives hbn expression in several specific cell lineages, and with largely overlapping patterns, suggesting the presence of shadow enhancers and enhancer redundancy. Specific enhancer deletion strains generated by gene targeting display developmental defects in the brain. This analysis opens an avenue for a deeper analysis of hbn regulatory elements in the future.
Authors: Arnim Jenett; Gerald M Rubin; Teri-T B Ngo; David Shepherd; Christine Murphy; Heather Dionne; Barret D Pfeiffer; Amanda Cavallaro; Donald Hall; Jennifer Jeter; Nirmala Iyer; Dona Fetter; Joanna H Hausenfluck; Hanchuan Peng; Eric T Trautman; Robert R Svirskas; Eugene W Myers; Zbigniew R Iwinski; Yoshinori Aso; Gina M DePasquale; Adrianne Enos; Phuson Hulamm; Shing Chun Benny Lam; Hsing-Hsi Li; Todd R Laverty; Fuhui Long; Lei Qu; Sean D Murphy; Konrad Rokicki; Todd Safford; Kshiti Shaw; Julie H Simpson; Allison Sowell; Susana Tae; Yang Yu; Christopher T Zugates Journal: Cell Rep Date: 2012-10-11 Impact factor: 9.423