Genomic structure, alternative splicing and tissue expression of rFrp/sFRP-4, the rat frizzled related protein gene.
Secreted frizzled related proteins (sFRP) are regulators of Wnt signaling pathways that play central roles in developmental processes and oncogenesis. Various sFRP genes have been cloned from different tissues and implicated in diverse biological activities. rFrp, the rat homologue of sFRP-4, was initially identified as being upregulated in mutant p53-induced cellular transformation. Here, we report on the isolation of five novel splice variants, rFrp/sFRP-4 II, II, III, IVa and IVb. The complete rFrp/sFRP-4 genomic structure spans over 31 kb covering 9 exons. Except for the variant IVb, which was derived from IVa by alternative polyadenylation signal, variants I to IVa were alternatively spliced to different exons in the 3'end of mRNA and resulted in transcripts with truncated open reading frame. The deduced proteins of the variants had truncated C-termini, however, the two key functional protein domains, the cysteine-rich domain and the netrin-like domain of the isoforms, were not altered. In addition, different transcriptional initiation sites were found with variants II and IV, implying that these variants may be regulated differently from the rFrp/sFRP-4. RT-PCR analysis showed that these splice variants displayed different patterns of tissue-specific expression. Northern blot analysis revealed that the rFrp/sFRP-4 is most abundant in the ovary. Taken together, our findings suggest that alternative splicing of rFrp/sFRP-4 plays a role in regulating tissue-specific expression. The truncated C terminals of rFrp/sFRP-4 variants may confer structural specificity and hence exert different biological functions in different tissues. Characterization of these novel splice variants should help to elucidate the function of the sFRP family gene.
Yam
Judy Wai Ping
JW
Biomedical Science, School of Chinese Medicine, Hong Kong Baptist University, Hong Kong, China.
Chan
Koon Wing
KW
Ngan
Elly Sau Wai
ES
Hsiao
W L Wendy
WL
D017398:Alternative Splicing / Q000502:physiology*; D000818:Animals; D000951:Antigens, Neoplasm; D001483:Base Sequence; D015152:Blotting, Northern / Q000379:methods; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D005091:Exons / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D009928:Organ Specificity / Q000502:physiology; D026723:Polyadenylation / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics*; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D051153:Wnt Proteins; D000094742:Secreted Frizzled-Related Proteins
D000951:Antigens, Neoplasm; D036341:Intercellular Signaling Peptides and Proteins; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D051153:Wnt Proteins; C498455:Sfrp4 protein, rat; D000094742:Secreted Frizzled-Related Proteins; C052646:sarcoma glycoprotein gp96 rejection antigens