Alternative splicing of mouse IL-15 is due to the use of an internal splice site in exon 5.
IL-15 is a pleiotropic cytokine modulating growth and differentiation of several hematopoietic cell types. Recently, we have demonstrated that mouse microglial cells, the brain macrophages, express both IL-15 and IL-15/IL-2 receptors. Based on single-cell RT-PCR data, we describe here an alternatively spliced IL-15 mRNA variant found in a small subpopulation of mouse microglia (5%, 3 out of 60 cells expressing IL-15 transcripts). PCR cycle sequencing of this larger transcript revealed the mouse homologue of the alternatively spliced exon A as it is known from the human IL-15 gene. Analysis of the corresponding mouse IL-15 gene region shows that the larger IL-15 transcript contains an yet unidentified 5' sequence of exon 5 while the shorter transcript uses an internal splice acceptor site. The mouse exon 5A segment has a length of 136 nt (17 nt longer than the human exon A). It contains five in-frame stop codons at its 5' end and a new translation initiation site at its 3' end. This new start site is surrounded by a favourable Kozak consensus sequence suggesting a more efficient translation rate. Further translational control by stem-loop binding factors is inferred by a predicted RNA stem-loop structure around the start site. Insertion of exon 5A would lead to an IL-15 polypeptide with a shortened leader sequence of 26 amino acids, as compared to the 48 amino acid leader sequence encoded by the transcript lacking exon 5A. Thus, the final IL-15 protein of the two splice variants is identical; different leader sequences could, however, lead to differences in the intracellular sorting, processing and/or secretion of IL-15.
Prinz
M
M
Max Delbrück Center for Molecular Medicine (MDC), Cellular Neurosciences, Robert-Rössle-Strasse 10, 13092, Berlin, Germany.
Hanisch
U K
UK
Kettenmann
H
H
Kirchhoff
F
F
D017398:Alternative Splicing / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D001923:Brain Chemistry / Q000235:genetics*; D002540:Cerebral Cortex / Q000166:cytology; D018387:Codon, Initiator / Q000235:genetics; D016384:Consensus Sequence; D005091:Exons / Q000235:genetics*; D019409:Interleukin-15 / Q000235:genetics*; D008264:Macrophages / Q000502:physiology; D051379:Mice; D017628:Microglia / Q000502:physiology*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000502:physiology
D018387:Codon, Initiator; D019409:Interleukin-15