title: Differential evolutionary wiring of the tyrosine kinase Btk.
abstract: BACKGROUND
  A central question within biology is how intracellular signaling pathways are maintained throughout evolution. Btk29A is considered to be the fly-homolog of the mammalian Bruton's tyrosine kinase (Btk), which is a non-receptor tyrosine-kinase of the Tec-family. In mammalian cells, there is a single transcript splice-form and the corresponding Btk-protein plays an important role for B-lymphocyte development with alterations within the human BTK gene causing the immunodeficiency disease X-linked agammaglobulinemia in man and a related disorder in mice. In contrast, the Drosophila Btk29A locus encodes two splice-variants, where the type 2-form is the more related to the mammalian Btk gene product displaying more than 80% homology. In Drosophila, Btk29A displays a dynamic pattern of expression through the embryonic to adult stages. Complete loss-of-function of both splice-forms is lethal, whereas selective absence of the type 2-form reduces the adult lifespan of the fly and causes developmental abnormalities in male genitalia.
  
  
  RESULTS
  Out of 7004-7979 transcripts expressed in the four sample groups, 5587 (70-79%) were found in all four tissues and strains. Here, we investigated the role of Btk29A type 2 on a transcriptomic level in larval CNS and adult heads. We used samples either selectively defective in Btk29A type 2 (Btk29A(ficP)) or revertant flies with restored Btk29A type 2-function (Btk29A(fic Exc1-16)). The whole transcriptomic profile for the different sample groups revealed Gene Ontology patterns reflecting lifespan abnormalities in adult head neuronal tissue, but not in larvae.
  
  
  CONCLUSIONS
  In the Btk29A type 2-deficient strains there was no significant overlap between transcriptomic alterations in adult heads and larvae neuronal tissue, respectively. Moreover, there was no significant overlap of the transcriptomic changes between flies and mammals, suggesting that the evolutionary conservation is confined to components of the proximal signaling, whereas the corresponding, downstream transcriptional regulation has been differentially wired.
authors.affiliation: Clinical Research Center, Department of Laboratory Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Huddinge, Stockholm, Sweden.
authors.forename: Hossain M
authors.initials: HM
authors.lastname: Nawaz
authors.forename: Per
authors.initials: P
authors.lastname: Kylsten
authors.forename: Noriko
authors.initials: N
authors.lastname: Hamada
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yamamoto
authors.forename: C I Edvard
authors.initials: CI
authors.lastname: Smith
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Lindvall
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology; D004251:DNA Transposable Elements / Q000235:genetics; D004331:Drosophila melanogaster / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D019143:Evolution, Molecular; D005260:Female; D020869:Gene Expression Profiling; D023281:Genomics; D006801:Humans; D008297:Male; D051379:Mice; D005810:Multigene Family / Q000235:genetics; D009474:Neurons / Q000166:cytology / Q000201:enzymology; D011505:Protein-Tyrosine Kinases / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D004251:DNA Transposable Elements; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C000625951:Btk protein, mouse