Expression of the alpha-fetoprotein gene in adult rat liver.
The adult rat liver contains three alpha-fetoprotein (AFP) mRNAs of 2.2 (minor), 1.7, and 1.5 kb. These transcripts share a common 3' sequence, but the 1.7- and 1.5-kb AFP mRNAs lack sequences present in the first seven 5' exons of the 2.2-kb AFP mRNA. S1 nuclease analysis maps the 1.7-kb mRNA at the 5' boundary of the eighth exon of the 2.2-kb AFP mRNA and the 1.5-kb mRNA in the middle of the eight exon. In a transformed fetal rat liver cell line, we have previously identified a 1.7-kb AFP mRNA which is encoded by an AFP cDNA (ARFP5) isolated from an adult rat liver cDNA library. The 90-bp 5' sequence of ARFP5, which is located in the seventh intron of the rat AFP gene, is not present in the 2.2-kb fetal AFP mRNA, although ARFP5 does contain nucleotide sequence present in the 2.2-kb AFP mRNA extending from the beginning of its eighth exon (nucleotide 873) to the 3' end. The 1.7-kb RNA in adult liver also hybridizes with the 90-bp 5' sequence of ARFP5, suggesting that the two 1.7-kb AFP mRNAs are similar. The developmental profile of these AFP transcripts shows that fetal rat liver contains mainly the 2.2-kb mRNA which decreases to a very low level around the fifth week after birth. The 1.7- and 1.5-kb AFP mRNAs can be visualized about the third and fourth weeks after birth, respectively, and are the major AFP mRNAs in the liver of rats that are older than 4 weeks. The levels of the AFP mRNAs in adult liver are approximately 0.4% of the AFP mRNA level in 18-day-old fetal liver. Both the 1.7- and 1.5-kb AFP mRNAs are actively translated; they direct the cell-free synthesis of two polypeptides of 50K and 44K. A 50K polypeptide is also the encoded product of the 1.7-kb mRNA in the transformed fetal rat liver cell line, suggesting that the 44K polypeptide may be encoded by the 1.5-kb AFP mRNA.
Wan
Y J
YJ
Human Genetics Branch, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Chou
J Y
JY
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004247:DNA / Q000032:analysis; D004586:Electrophoresis / Q000379:methods; D004720:Endonucleases; D005333:Fetus / Q000378:metabolism; D008099:Liver / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D009693:Nucleic Acid Hybridization; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains / Q000254:growth & development; D015719:Single-Strand Specific DNA and RNA Endonucleases; D014158:Transcription, Genetic; D000509:alpha-Fetoproteins / Q000096:biosynthesis / Q000235:genetics*
D012333:RNA, Messenger; D000509:alpha-Fetoproteins; D004247:DNA; D004720:Endonucleases; D015719:Single-Strand Specific DNA and RNA Endonucleases