Hepatocyte differentiation in culture. Appearance of tyrosine aminotransferase

Abstract

Liver of rat foetuses from 14 to 19 days of gestation and cultured hepatocytes derived from foetuses of 14 or 15 days gestation show a limited capacity to transaminate tyrosine. This low tyrosine transamination activity can be ascribed to aspartate aminotransferase. Definitive tyrosine aminotransferase can be demonstrated in 1-day-old cultures of hepatocytes taken from 19-day foetuses, but not from 15-day foetuses. However, after 3 days of culture hepatocytes from 15-day foetuses are able to synthesize tyrosine aminotransferase. Induction studies reveal that dexamethasone is capable of increasing tyrosine aminotransferase activity once it is detectable in culture.

Tyrosine aminotransferase induction in hepatocytes cultured from rat foetuses treated with dexamethasone in utero

“…Although the sensitive radiochemical assay detects significant transamination of tyrosine of about the same activity in controls and test animals, it has been demonstrated that this can be ascribed to the non-specific activity of aspartate aminotransferase (Yeoh et al, 1979). This is consistent with the findings of Greengard & Dewey (1967) and Cake et al (1973).…”

The Ontogeny of Apolipoprotein Expression in Rat Liver. mRNA Levels in Developing Liver and Cultured Fetal Rat Hepatocytes

“…This is in contrast to the levels of the respective lipoprotein mRNAs seen in vivo which suggests that the uterine environment might suppress expression of apo E. This is also supported by the substantial increase in apo E mRNA observed when freshly isolated and 1-day-cultured hepatocytes are compared. This is similar to the situation which exists for tyrosine aminotransferase, a liver-specific enzyme which can be prematurely induced when 19-day gestation fetal rat hepatocytes are placed in culture (Yeoh et al, 1979). Cake et al (1989) have proposed that high circulating levels of insulin in the fetus is an important factor which suppresses tyrosine aminotransferase expression in utero.…”

“…The fetal age difference spanned the period when apo E expression was initiated in vivo and it was of interest to determine whether the immature hepatocytes will undergo this transition in culture. We have previously shown that 15-day gestation hepatocytes maintained in dexamethasone-supplemented medium will initiate synthesis of the developmentally regulated liver-specific enzyme tyrosine aminotransferase (Yeoh et al, 1979). Surprisingly, apo E was expressed in standard cultures established from 15-day gestation liver at similar levels to those observed for apo A-I and A-IV.…”

“…Cultures of fetal hepatocytes were prepared as previously described (Yeoh et al, 1979). Briefly, livers derived from 19-day gestation rats were aseptically removed from fetuses and diced using a Mickle chopper (Mickle Laboratories Engineering Co., Surrey, UK) fitted with a razor blade.…”

5′ Sequences Direct Developmental Expression and Hormone Responsiveness of Tyrosine Aminotransferase in Primary Cultures of Fetal Rat Hepatocytes

“…Primary cultures of fetal rat hepatocytes [6,71 have been used to study the effects of glucocorticoids, Bt,cAMP and insulin on the developmental appearance of TyrAT. Consistent with results in vivo, TyrAT activity in cultured fetal hepatocytes is inducible by dexamethasone [6] and Bt,cAMP [8] and the synergistic effect of these two agents is retained [8].…”