Sequence analysis of a processed gene coding for mouse ribosomal protein L32

Vitamin A depletion is associated with low phosphoenolpyruvate carboxykinase mRNA levels during late fetal development and at birth in mice

Expression of the phosphoenolpyruvate carboxykinase (PEPCK) gene is repressed during fetal liver development and activated at birth. It has been shown that the PEPCK gene is a retinoid-responsive gene, but whether it is regulated by vitamin A in the fetus has not been established. In this study, we found that PEPCK mRNA can be detected in the murine fetal liver as early as gestational d 17. In addition, expression and cAMP induction of the PEPCK gene during late gestation and at birth require vitamin A sufficiency in the fetus and neonate. The PEPCK promoter contains several regulatory elements that bind a diverse array of transcription factors and nuclear coregulators, although it is largely unknown which of these factors are expressed early in liver development. Expression of some of these nuclear factors in livers of fetal mice was investigated by immunohistochemistry (IHC). Fetuses were from dams that were fed from the beginning of gestation diets that were adequate or devoid of vitamin A. Hepatocyte nuclear factor 4alpha (HNF4alpha) was expressed at the earliest stage of liver development on d 11, whereas retinoid X receptor alpha (RXRalpha) and nuclear coactivator CREB-binding protein (CBP) were expressed from d 16 onward. Although expressions of RXRalpha and CBP in livers of vitamin A-sufficient and vitamin A-depleted fetal mice did not differ, the level of HNF4alpha was consistently lower in the latter. Our findings strongly suggest that vitamin A is required during liver development for staged expression of the PEPCK gene and that HNF4alpha may be involved in mediating vitamin A regulation of the PEPCK gene at these critical periods.

Anoxic induction of a sarcoma virus-related VL30 retrotransposon is mediated by a cis-acting element which binds hypoxia-inducible factor 1 and an anoxia-inducible factor

Cells exposed to hypoxia undergo substantial changes in gene expression generally associated with metabolic adaptation and increasing oxygen delivery. In contrast, responses distinct from those elicited by hypoxia are induced in anoxic fibroblasts; this includes activation of a set of VL30 elements. The responses seen in anoxically cultured fibroblasts are expressed physiologically in vivo during the anaerobic phase of wound healing. A fundamental question is whether transcriptional regulatory pathways utilized during anoxia are distinct from those already characterized for hypoxic cells. We report here the isolation of a 14-bp sequence within a VL30 retrotransposon promoter which mediates its anoxia responsiveness. Analyses of the protein complexes binding to this sequence demonstrated the presence of two distinct inducible DNA binding activities. The first is present in both hypoxic and anoxic fibroblasts and is indistinguishable from hypoxia-inducible factor 1. The second activity, which is present only in anoxic fibroblasts, is a previously uncharacterized heterodimeric DNA binding activity that appears to arise via posttranslational modification of an existing complex found in aerobic cells. These results indicate that the strong VL30 transcriptional induction seen with anoxia occurs through a mechanism specific to anoxia.