The proline-histidine-rich CDK2/CDK4 interaction region of C/EBPalpha is dispensable for C/EBPalpha-mediated growth regulation in vivo.

The C/EBPalpha transcription factor regulates growth and differentiation of several tissues during embryonic development. Several hypotheses as to how C/EBPalpha inhibits cellular growth in vivo have been derived, mainly from studies of tissue culture cells. In fetal liver it has been proposed that a short, centrally located, 15-amino-acid proline-histidine-rich region (PHR) of C/EBPalpha is responsible for the growth-inhibitory function of the protein through its ability to interact with CDK2 and CDK4, thereby inhibiting their activities. Homozygous Cebpa(DeltaPHR/DeltaPHR) (DeltaPHR) mice, carrying a modified cebpa allele lacking amino acids 180 to 194, were born at the Mendelian ratio, reached adulthood, and displayed no apparent adverse phenotypes. When fetal livers from the DeltaPHR mice were analyzed for their expression of cell cycle markers, bromodeoxyuridine incorporation, cyclin-dependent kinase 2 kinase activity, and global gene expression, we failed to detect any cell cycle or developmental differences between the DeltaPHR mice and their control littermates. These in vivo data demonstrate that any C/EBPalpha-mediated growth repression via the PHR as well as the basic region is dispensable for proper embryonic development of, and cell cycle control in, the liver. Surprisingly, control experiments performed in C/EBPalpha null fetal livers yielded similar results.

Characteristics of gastrin controlled ECL cell specific gene expression.

BACKGROUND: The ECL cells are histamine-producing endocrine cells in the oxyntic mucosa that synthesize and secrete proteins and peptides. They are the primary target for gastrin and mediate the control of gastrin on acid secretion and oxyntic mucosal growth. Knowledge of the molecular biology of the ECL cell is therefore important for understanding gastric physiology. Accordingly, we wanted to identify genes that are characteristically expressed in the ECL cells and controlled by gastrin. METHODS: Using Affymetrix GeneChips, RNA expression profiles were generated from ECL cells isolated by counterflow elutriation from hyper- or hypogastrinemic rats. Contamination from non-endocrine cells was eliminated by subtraction of the expression profiles of the fundic and antral mucosa. RESULTS: The expression of 365 genes was ECL cell characteristic. Gastrin was found to control the expression of 120 which could be divided into two major groups depending on the known or anticipated biological function of the encoded protein: genes encoding proteins involved in the secretory process and genes encoding proteins needed to generate energy for secretion. Interestingly, gastrin stimulation also increased ECL cells expression of anti-apoptotic genes. CONCLUSION: The ECL cell specific expression profile is reminiscent of that of neurons and other endocrine cells exhibiting high expression of genes encoding proteins involved in the synthesis, storage and secretion of neuropeptides or peptide hormones. Gastrin regulated the expression of one third of these genes and is thus involved in the control of secretion from the ECL cells.

Evaluation in mammalian oocytes of gene transcripts linked to epigenetic reprogramming.

The mature mammalian metaphase II (MII) oocyte has a unique ability to reprogram sperm chromatin and support early embryonic development. This feature even extends to the epigenetic reprogramming of a terminally differentiated cell nucleus as observed in connection with somatic cell nuclear transfer. Epigenetic nuclear reprogramming is highly linked to chromatin structure and includes covalent modifications of DNA and core histone proteins as well as reorganization of higher-order chromatin structure. A group of conserved enzymes mediating DNA methylation, methyl-CpG-binding protein (MeCP), histone acetylation and methylation, and chromatin remodeling are extensively involved in epigenetic reprogramming in mammalian cells. Using the oligonucleotide microarray technique, the present study compared the expression levels of 86 genes associated with epigenetic reprogramming in murine in vivo matured MII oocytes with that of germinal vesicle oocytes. Correlation between biological replicates was high. A total of 57 genes with potential reprogramming effect were detected. In MII oocytes, four genes were significant up-regulated, whereas 18 were down-regulated and 35 unchanged. The significantly regulated genes were validated by real-time quantitative RT-PCR. For example, MII oocytes showed a significant down-regulation of oocyte-specific maintenance DNA methyltransferase, Dnmt1o, and up-regulation of MeCP transcript, methyl-CpG binding domain protein 2. Furthermore, histone acetyltransferases were proportionally overrepresented when compared with histone deacetylases. These data elucidate for the first time some of the mechanisms that the oocyte may employ to reprogram a foreign genome either in form of a spermatozoa or a somatic nucleus and may thus be of importance for advancing the fields of stem cell research and regenerative medicine.