Expression of the albumin and alphafetoprotein genes in the mouse : analysis of post-transcriptional nuclear events

The expression of the albumin and alphafetoprotein (AFP) genes of the mouse has been studied with particular emphasis on nuclear events following transcription. Using RNA blot and hybridization techniques, high molecular weight nuclear RNA has been examined from three different tissue sources. Nuclear RNA from adult liver was shown to contain multiple albumin specific species that were large molecular weight, polyadenylated and demonstrated a reproducible set of band intensities. When newborn mouse liver and hepatoma tissues, which also synthesize AFP, were analyzed qualitatively similar AFP precursor bands were detected including one that possibly represents the AFP primary transcript. The albumin RNA pre cursors, when analyzed in tissues that also synthesize AFP, reveal an alteration of the characteristic adult bands that may be related to the expression of a fetal-like phenotype.

Structural analysis of the albumin gene revealed that intron 12 contains a sequence that is highly repeated in the mouse genome and most likely has appeared in this location as a result of an evolutionarily recent transposition event. The intron 12 region and three others that were shown to contain unique sequence regions were subcloned into the plasmid vector pBR322 for use in further studies.

Hybridization of intron regions to nuclear RNA blots suggested that processing of the albumin RNA precursors occurs via a preferred pathway in agreement with other high abundance mRNA genes. Some of the albumin nuclear RNA precursors were shown to be associated with the nuclear protein matrix, a result which supports a function for this structure as the site for RNA processing. These data are discussed in light of possible regulatory events affecting these genes during RNA processing in the nucleus.