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Human fibronectin: molecular cloning evidence for two mRNA species differing by an internal segment coding for a
Abstract:
Two different fibronectin (FN) mRNA species were detected in the human cell line Hs578T. One species, mRNA I, contains an additional 270 nucleotide long insert (ED) that encodes exactly one of the internally repeated structural domains of the protein. The 90 amino acid extra domain belongs to the so-called type III homology and it is located in the carboxy-terminal half of FN, in between the cell attachment and the heparin binding sites of the protein. The evidence of two mRNAs is provided by the isolation and characterisation of four independent cDNA clones from a library prepared with a synthetic oligonucleotide primer, and it was confirmed by S1 nuclease analysis of cDNA/mRNA hybrids. This kind of analysis also showed that in the human cell line, mRNA I is present at a lower level than mRNA II (the mRNA species without the ED), whilst in human liver, mRNA I is virtually undetectable. Since liver tissue has recently been reported to be the source of plasma FN, our results indicate that the presence of the ED insert could be a particular feature of cellular FN.
Insights
Researchers found two fibronectin (FN) mRNA types in human cells. One type, mRNA I, has an extra domain (ED) not found in liver fibronectin, suggesting it’s specific to cellular FN.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Fibronectin (FN) is a crucial extracellular matrix protein involved in cell adhesion and tissue repair.
- Differential expression of FN mRNA species can lead to distinct protein isoforms with varying functions.
Purpose of the Study:
- To investigate the existence and characteristics of different fibronectin mRNA species in human cells.
- To determine the tissue-specific distribution of these fibronectin mRNA variants.
Main Methods:
- Isolation and characterization of complementary DNA (cDNA) clones from a human cell line (Hs578T).
- Utilizing S1 nuclease analysis to compare cDNA/mRNA hybrids and confirm mRNA species.
- Quantification of mRNA I and mRNA II levels in both cell lines and human liver tissue.
Main Results:
- Two distinct fibronectin mRNA species, mRNA I and mRNA II, were identified in the Hs578T cell line.
- mRNA I contains a 270-nucleotide insert (ED) encoding a type III homology domain, absent in mRNA II.
- mRNA I was found at lower levels in Hs578T cells and was virtually undetectable in human liver tissue.
Conclusions:
- The presence of the extra domain (ED) in fibronectin mRNA appears to be a distinguishing feature of cellular fibronectin.
- This finding suggests differential splicing of fibronectin mRNA may generate tissue-specific isoforms.