The mouse B-raf gene encodes multiple protein isoforms with tissue-specific expression.
The c-Rmil/B-raf proto-oncogene is a member of the mil/raf family encoding serine/threonine protein kinases shown to be involved in signal transduction from the membrane to the nucleus. We isolated from a mouse brain library B-raf cDNAs containing a previously unidentified 36-base pair alternatively spliced exon located between exons 8 and 9 and, therefore, designated exon 8b. Human and mouse B-raf mRNAs also contain the 120-base pair alternatively spliced exon 10 previously described in the avian c-Rmil gene. Independent splicing of these two exons, located between the conserved region 2 (CR2) and the catalytic domain (CR3) gives rise to mRNAs potentially encoding four distinct proteins. By using specific sera generated against different portions of B-Raf, we identified at least 10 protein isoforms in adult mouse tissues. Some isoforms, in the range of 69-72 kDa, are not recognized by antisera directed against peptides encoded by exons 1 and 2, indicating the existence of B-Raf proteins with two different NH2 extremities. The other isoforms, in the range of 79-99 kDa, contain the amino acids encoded by exons 1 and 2, by either or both of the alternatively spliced exons, and, possibly, by another of the unidentified exon. Analysis of B-raf mRNA expression by reverse transcriptase-polymerase chain reaction and immunocharacterization of B-Raf proteins in different tissues of the adult mouse showed a tissue-specific pattern of B-Raf isoforms expression. Interestingly, isoforms containing amino acids encoded by exon 10 are specifically expressed in neural tissues. Taken together, these results suggest that distinct B-Raf proteins could be involved, in a tissue-specific manner, in signal transduction pathways.
Barnier
J V
JV
Unité Mixte de Recherche 146 du CNRS, Institut Curie, Centre Universitaire, Orsay, France.
Papin
C
C
Eychène
A
A
Lecoq
O
O
Calothy
G
G
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D001483:Base Sequence; D001717:Birds; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D005091:Exons; D015870:Gene Expression; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011519:Proto-Oncogenes; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014018:Tissue Distribution
D017931:DNA Primers; D018076:DNA, Complementary; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf