CONSTRUCTION OF A GENE-EXPRESSION PROFILE OF A HUMAN FETAL LIVER BY SINGLE-PASS CDNA SEQUENCING

We have obtained an overall gene expression profile of a human fetal l iver by sequencing the 5' ends of random cDNA clones from an unbiased cDNA library, As a result, many novel genes that might be related to l iver growth and hemopoiesis have been identified, Poly (A)(+) RNA was purified from the liver of a human fetus obtained at the 22nd week of gestation, and a directional library was constructed with oligo d(T)-p rimed cDNAs synthesized without any normalizing procedures, The 5' end of each randomly chosen clone was sequenced by the dideoxy-chain term ination methods, and each sequence was used for homology search in the public databases such as GenBank, SWISS-PROT, and PIR. Of 1231 random cDNA clones analyzed, 697 clones representing 204 different transcrip ts (57%), were identical to previously known human genes. The spectrum of the genes in this category reflected well the physiological charac teristics of the fetal liver, a combination of hepatic and hemopoietic functions. About 4% of the clones represented novel gene transcripts with significant homologies to known genes of human or other organisms . These included several genes that are known to be involved in cellul ar differentiation and/or proliferation. About 25% of the clones had n o statistically significant match to any known genes. In summary, we h ave identified 546 different gene transcripts consisting of 204 known human genes, 42 homologous genes, and 300 unknown genes. Thus, this ap proach appears to be a highly efficient way to identify novel genes of biological interest.