title: Characterization of Drosophila GDNF receptor-like and evidence for its evolutionarily conserved interaction with neural cell adhesion molecule (NCAM)/FasII.
abstract: BACKGROUND
  Glial cell line-derived neurotrophic factor (GDNF) family ligands are secreted growth factors distantly related to the TGF-β superfamily. In mammals, they bind to the GDNF family receptor α (Gfrα) and signal through the Ret receptor tyrosine kinase. In order to gain insight into the evolution of the Ret-Gfr-Gdnf signaling system, we have cloned and characterized the first invertebrate Gfr-like cDNA (DmGfrl) from Drosophila melanogaster and generated a DmGfrl mutant allele.
  
  
  RESULTS
  We found that DmGfrl encodes a large GPI-anchored membrane protein with four GFR-like domains. In line with the fact that insects lack GDNF ligands, DmGfrl mediated neither Drosophila Ret phosphorylation nor mammalian RET phosphorylation. In situ hybridization analysis revealed that DmGfrl is expressed in the central and peripheral nervous systems throughout Drosophila development, but, surprisingly, DmGfrl and DmRet expression patterns were largely non-overlapping. We generated a DmGfrl null allele by genomic FLP deletion and found that both DmGfrl null females and males are viable but display fertility defects. The female fertility defect manifested as dorsal appendage malformation, small size and reduced viability of eggs laid by mutant females. In male flies DmGfrl interacted genetically with the Drosophila Ncam (neural cell adhesion molecule) homolog FasII to regulate fertility.
  
  
  CONCLUSIONS
  Our results suggest that Ret and Gfrl did not function as an in cis receptor-coreceptor pair before the emergence of GDNF family ligands, and that the Ncam-Gfr interaction predated the in cis Ret-Gfr interaction in evolution. The fertility defects that we describe in DmGfrl null flies suggest that GDNF receptor-like has an evolutionarily ancient role in regulating male fertility and a previously unrecognized role in regulating oogenesis.
  
  
  CONCLUSIONS
  These results shed light on the evolutionary aspects of the structure, expression and function of Ret-Gfrα and Ncam-Gfrα signaling complexes.
authors.affiliation: Institute of Biotechnology, Viikinkaari 9, Viikki Biocenter, University of Helsinki, Helsinki, Finland. jukka.kallijarvi@helsinki.fi
authors.forename: Jukka
authors.initials: J
authors.lastname: Kallijärvi
authors.forename: Vassilis
authors.initials: V
authors.lastname: Stratoulias
authors.forename: Kristel
authors.initials: K
authors.lastname: Virtanen
authors.forename: Ville
authors.initials: V
authors.lastname: Hietakangas
authors.forename: Tapio I
authors.initials: TI
authors.lastname: Heino
authors.forename: Mart
authors.initials: M
authors.lastname: Saarma
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002490:Central Nervous System / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism*; D004843:Epistasis, Genetic; D005260:Female; D005298:Fertility / Q000235:genetics; D058851:GPI-Linked Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D023061:Gene Order; D006031:Glycosylation; D008297:Male; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000235:genetics; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D009865:Oocytes / Q000254:growth & development / Q000378:metabolism; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D020033:Protein Isoforms; D021381:Protein Transport; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; D029721:Drosophila Proteins; D058851:GPI-Linked Proteins; C581827:Gfrl protein, Drosophila; D020033:Protein Isoforms; C051642:fasciclin II; D051096:Proto-Oncogene Proteins c-ret; C416649:Ret protein, Drosophila