Molecular cloning, genomic organization, developmental regulation, and a knock-out mutant of a novel Leu-rich repeats-containing G protein-coupled receptor (DLGR-2) from Drosophila melanogaster

After screening the Berkeley Drosophila Genome Project database with sequen ces From a recently characterized Leu-rich repeats-containing G protein-cou pled receptor [LGR) from Drosophila (DLGR-1), we identified a second gene f or a different LGR (DLGR-2) and cloned its cDNA. DLGR-2 is 1360 amino acid residues long and shows a striking structural homology with members of the glycoprotein hormone [thyroid-stimulating hormone [TSH); follicle-stimulati ng hormone [FSH); luteinizing hormone/choriogonadotropin (LH/CG)] receptor family from mammals and with two additional, recently identified mammalian orphan LGRs (LGR-4 and LCR-S). This homology includes the seven transmembra ne region (e.g., 49% amino acid identify with the human TSH receptor) and t he very large extracellular amino terminus. This amino terminus contains 18 Leu-rich repeats-in contrast with the 3 mammalian glycoprotein hormone rec eptors and DLGR-1 that contain 9 Leu-rich repeats, but resembling the mamma lian LGR-4 and LGR-5 that each have 17 Leu-rich repeats in their amino term ini. The DLGR-2 gene is >18.6 kb pairs long and contains 15 exons and 14 in trons. Four intron positions coincide with the intron positions of the thre e mammalian glycoprotein hormone receptors and have the same intron phasing , showing that DLGR-2 is evolutionarily related to these mammalian receptor s. The DLGR-2 gene is located at position 34E-F on the left arm of the seco nd chromosome and is expressed in embryos and pupae but not in larvae and a dult flies. Homozygous knock-out mutants, where the DLGR-2 gene is interrup ted by a P element insertion, die around the time of hatching. This Ending, together with the expression data, strongly suggests that DLGR-2 is exclus ively involved in development.