Expression of aldolase isozyme mRNAs in fetal rat liver

Abstract

The regulation of aldolase isozyme expression during development was studied by measuring the concentrations of mRNAs coding for aldolase A and B subunits in fetal and adult rat liver. Poly(A)-containing RNAs were extracted from livers at various stages of development of fetal rats, and the aldolase A and B subunits in the in vitvo translation products of these RNAs ware analyzed immunologically. The content of aldolase B mRNA in 14-day fetal liver, measured quantitatively as translational activity, was somewhat smaller than that of aldolase A mRNA; immunologically precipitable aldolase B and A amounted to 0.06 and 0.25 %, respectively, of the total products. Similar experiments using RNAs from fetuses at later stages, however, showed that aldolase B mRNA increased during development, whereas aldolase A mRNA decreased. In newborn rat liver, aldolase B constituted 0.56 of the total translation products of mRNA, but there was little detectable aldolase A (0.03 yo).The changes of aldolase mRNA levels were analyzed further by northern blot and dot-blot hybridization experiments using cloned aldolase A and B cDNAs. The content of aldolase B mRNA increased in the fetal stage, and that in newborn rat liver was about 12 times that in 14-day fetal liver. In contrast, the aldolase A mRNA content decreased during gestation and that in newborn rat liver was about one-eighth of that in 14-day fetal liver. These observations suggest that the switch of aldolase isozyme expression in fetal liver is controlled by the levels of the respective mRNAs.The glycolytic enzyme, fructose-I ,6-bisphosphate aldolase, is a tetrameric protein composed of a specific combination of subunits A, B and C. The three subunits can interact with each other to form an active tetraneric enzyme both in vivo and in vitro [l -31, suggesting structural resemblance of the subunits. However, the expression of each subunit is controlled independently. The accumulations of these subunits are tissuespecific or organ-specific in normal animals; aldolase A subunit is predominant in muscle cells, whereas the B subunit is produced in liver cells, and the C subunit is synthesized in brain cells [4]. Moreover, change in the isozyme: pattern in fetal liver during development has been observed. In rat fetal liver, aldolase subunits A and C are present in addition to the B subunit, but the A and C subunits disappear during development and consequently the B subunit is predominant in adult liver cells [5,6]. Further, resurgence of fetal-type aldolase A and disappearance of aldolase B have been observed in various hepatoma cells [7 -91 and during chemilcal carcinogenesis in liver cells [lo, 111. The abilities of the subunits to interact with each other imply their structural resemblance, and indeed our sequence studies on cloned aldolase B cDNA suggested high homology between the aldolase A and B subunits [12]. Furthermore, the possible structural resemblance of these subunits suggests that the genes for aldolase subunits are evolved from the same ancestral gene. If thi...

Proto‐oncogene c‐jun and c‐fos messenger RNAs increase in the liver of carnitine‐deficient juvenile visceral steatosis (jvs) mice

“…0~-Fetoprotein, a major fetus serum protein, and aldolase A, a muscle-type isozyme of aldolaso are known to be highly expressed in fetal liver and even in adult liver during hepatoc, arcinogenesis [10,11,18,19]. We …”

“…The proto-oncogenes, c-jun and c-fos, coding for nuclear proteins regulate cell growth and differentiation by controlling gene transcription through AP-1 enhancer element [13,14]. To further study abnormal gene expression in the liver of jvs mice, we determined the levels of c-jun, c-los, o~- highly in undifferentiated or de-differentiated hepatocytes [10,11,[15][16][17][18][19].…”

Transcriptional control of the rat hepatic CYP2E1 gene.

“…No differences were noted in the DNase footprinting pattern of the HNF-1 region when fetal and adult liver extracts were compared. Others have recently demonstrated that the liver-specific aldolase B gene is activated in late fetal rats as early as day 16 of gestation (28) and that its in vitro transcription is dependent on the presence of an HNF-1 binding site and a second site, designated AiF-B, that contained a CCAAT motif (40). These investigators demonstrated that the HNF-1 binding component increased at day 15 of gestation, but this increase did not correlate with in vitro transcription.…”

An Intronic Enhancer Essential for Tissue-specific Expression of the Aldolase B Transgenes

“…Developmental Regulation of the Aldolase B 1600ABC/CAT Transgene in the Liver-Expression of the aldolase B gene in the liver is developmentally regulated; the mRNA is undetectable before day 14 of gestation, and from that stage to adult it was estimated to increase about 9-fold (Numazaki et al, 1984;Schapira et al, 1975). Using the line 7 expressing the 1600ABC/CAT transgene at a high level, we observed that developmental regulation of transgene expression mimics that of the endogenous aldolase B gene (Table II).…”