Biomedical subjects

A Bilger

Publications and source records attributed to A Bilger.

9 recordsLinked to original sources

PubMed2000

The Mom1AKR intestinal tumor resistance region consists of Pla2g2a and a locus distal to D4Mit64.

The Mom1 (Modifier of Min-1) region of distal chromosome 4 was identified during a screen for polymorphic modifiers of intestinal tumorigenesis in ApcMin/+ mice. Here, we demonstrate that the Mom1AKR allele consists of two genetic components. These include the secretory phospholipase Pla2g2a, whose candidacy as a Mom1 resistance modifier has now been tested with several transgenic lines. A second region, distal to Pla2g2a, has also been identified using fine structure recombinants. Pla2g2aAKR transgenic mice demonstrate a modest resistance to tumorigenesis in the small intestine and a very robust resistance in the large intestine. Moreover, the tumor resistance in the colon of Pla2g2aAKR animals is dosage-dependent, a finding that is consistent with our observation that Pla2g2a is expressed in goblet cells. By contrast, mice carrying the distal Mom1 modifier demonstrate a modest tumor resistance that is confined to the small intestine. Thus, the phenotypes of these two modifier loci are complementary, both in their quantitative and regional effects. The additive effects and tight linkage of these modifiers may have been necessary for the initial identification of the Mom1 region.

Adenomatous Polyposis Coli↗

PubMed1999

The cleavage and polyadenylation specificity factor in Xenopus laevis oocytes is a cytoplasmic factor involved in regulated polyadenylation.

During early development, specific mRNAs receive poly(A) in the cytoplasm. This cytoplasmic polyadenylation reaction correlates with, and in some cases causes, translational stimulation. Previously, it was suggested that a factor similar to the multisubunit nuclear cleavage and polyadenylation specificity factor (CPSF) played a role in cytoplasmic polyadenylation. A cDNA encoding a cytoplasmic form of the 100-kDa subunit of Xenopus laevis CPSF has now been isolated. The protein product is 91% identical at the amino acid sequence level to nuclear CPSF isolated from Bos taurus thymus. This report provides three lines of evidence that implicate the X. laevis homologue of the 100-kDa subunit of CPSF in the cytoplasmic polyadenylation reaction. First, the protein is predominantly localized to the cytoplasm of X. laevis oocytes. Second, the 100-kDa subunit of X. laevis CPSF forms a specific complex with RNAs that contain both a cytoplasmic polyadenylation element (CPE) and the polyadenylation element AAUAAA. Third, immunodepletion of the 100-kDa subunit of X. laevis CPSF reduces CPE-specific polyadenylation in vitro. Further support for a cytoplasmic form of CPSF comes from evidence that a putative homologue of the 30-kDa subunit of nuclear CPSF is also localized to the cytoplasm of X. laevis oocytes. Overexpression of influenza virus NS1 protein, which inhibits nuclear polyadenylation through an interaction with the 30-kDa subunit of nuclear CPSF, prevents cytoplasmic polyadenylation, suggesting that the cytoplasmic X. laevis form of the 30-kDa subunit of CPSF is involved in this reaction. Together, these results indicate that a distinct, cytoplasmic form of CPSF is an integral component of the cytoplasmic polyadenylation machinery.

Amino Acid Sequence↗

PubMed1996

Manipulation of the mouse germline in the study of Min-induced neoplasia.

The Min mouse, generated by random germline mutagenesis, carries a mutation in the mouse homolog of APC and is a model of inherited human intestinal tumorigenesis. To identify other genes in the pathway(s) of intestinal tumorigenesis, genes that modify the Min phenotype have been sought. Several have been identified, including Mom1 and the genes for the 5-cytosine DNA methyltransferase and the DNA mismatch repair factor Msh2. Min-dependent tumorigenesis also occurs in mammary glands, the pancreas, and the body wall. The Min mouse has therefore become a model for tumorigenesis in a variety of organs. Identifying modifiers of its phenotype will help in piecing together the pathways of tumorigenesis in each of these tissues.

Animals↗

PubMed1995

Poly (A) polymerases in the nucleus and cytoplasm of frog oocytes: dynamic changes during oocyte maturation and early development.

Poly(A) can be added to mRNAs both in the nucleus and in the cytoplasm. During oocyte maturation and early embryonic development, cytoplasmic polyadenylation of preexisting mRNAs provides a common mechanism of translational control. In this report, to begin to understand the regulation of polyadenylation activities during early development, we analyze poly (A) polymerases (PAPs) in oocytes and early embryos of the frog, Xenopus laevis. We have cloned and sequenced a PAP cDNA that corresponds to a maternal mRNA present in frog oocytes. This PAP is similar in size and sequence to mammalian nuclear PAPs. By immunoblotting using monoclonal antibodies raised against human PAP, we demonstrate that oocytes contain multiple forms of PAP that display different electrophoretic mobilities. The oocyte nucleus contains primarily the slower migrating forms of PAP, whereas the cytoplasm contains primarily the faster migrating species. The nuclear forms of PAP are phosphorylated, accounting for their retarded mobility. During oocyte maturation and early postfertilization development, preexisting PAPs undergo regulated phosphorylation and dephosphorylation events. Using the cloned PAP cDNA, we demonstrate that the complex changes in PAP forms seen during oocyte maturation may be due to modifications of a single polypeptide. These results demonstrate that the oocyte contains a cytoplasmic polymerase closely related to the nuclear enzyme and suggest models for how its activity may be regulated during early development.

Amino Acid Sequence↗

PubMed1994

Nuclear polyadenylation factors recognize cytoplasmic polyadenylation elements.

In the cytoplasm of oocytes and early embryos, addition of poly(A) to mRNAs can activate their translation. We demonstrate that despite many differences between poly(A) addition in the cytoplasm and nucleus, these two forms of polyadenylation may involve identical trans-acting factors. Nuclear polyadenylation requires the sequence AAUAAA, the AAUAAA-binding cleavage and polyadenylation specificity factor (CPSF), and a poly(A) polymerase (PAP). We show that CPSF and PAP, purified from calf thymus, exhibit the same sequence specificity observed in the cytoplasm during frog oocyte maturation, requiring both AAUAAA and a proximal U-rich sequence. The enhanced polyadenylation of RNAs containing U-rich sequences is caused by their increased affinity for CPSF. Frog nuclear polyadenylation factors display cytoplasmic sequence specificity when dilute, suggesting that a difference in their concentrations in the nucleus and cytoplasm underlies the different sequence specificities in the two compartments. Because polyadenylation in extracts prepared from oocytes before maturation is stimulated by addition of CPSF, the onset of polyadenylation during early development may be attributable to the activation or synthesis of a CPSF-like factor. We suggest that sequences upstream of AAUAAA that are required for cleavage and polyadenylation of certain pre-mRNAs in the nucleus may be functionally equivalent to the upstream, U-rich sequences that function in the cytoplasm, enhancing CPSF binding. We propose that CPSF and PAP comprise a core polyadenylation apparatus in the cytoplasm of oocytes and early embryos.

Animals↗

PubMed1993

Regional cerebral blood flow response to acute hypoxia changes with postnatal age in the rat.

The quantitative autoradiographic [14C]iodoantipyrine technique was applied to measure the effects of an acute hypoxic exposure on rates of local cerebral blood flow (LCBF) in the 10 (P10)-, 14 (P14)- and 21 (P21)-day-old rat. The animals were exposed to hypoxic (7% O2/93% N2) or control gas mixtures (21% O2/79% N2) for 40 min before the initiation of the 1-min LCBF measurement. At P10, hypoxia induced a 142-415% increase in LCBF over control levels, which affected the 45 structures studied. The highest increases in LCBF were noticed in posterior midbrain and brainstem regions. These increases are in good accordance with hypoxia-induced increases in LCBF recorded during acute hypoxia exposure in both newborn and adult animals. At P14 and P21, rates of LCBF decreased with hypoxia. These decreases were significant in 23 and 21 brain regions, respectively, belonging to all systems studied. These changes in LCBF are in quite good correlation with our previous data on the effects of acute hypoxia exposure on cerebral glucose utilization but the decrease in LCBF is of higher amplitude than the one in cerebral glucose utilization translating into a relative hypoperfusion at a constant metabolic level at P14 and P21. However, arterial blood pressure was reduced by 16 mmHg and arterial pCO2 was significantly decreased at the two latter ages in hypoxic animals compared to controls. These two systemic factors, and mainly hypocapnia, are rather responsible for the cerebral hypoperfusion recorded at P14 and P21 in hypoxic rats whereas the circulatory response seems to be predominantly hypoxic at P10.

Analysis of Variance↗

PubMed1992

Acute hypoxia induces specific changes in local cerebral glucose utilization at different postnatal ages in the rat.

The quantitative autoradiographic 2-[14C]-deoxyglucose technique (2-DG) was applied to measure the effects of an acute hypoxic exposure on local cerebral metabolic rates for glucose (LCMRglcs) in the 10 (P10)-, 14 (P14)-, and 21 (P21)-day-old rat. The animals were exposed to hypoxic (7% O2/93% N2) or control gas mixture (21% O2/79% N2) for 20 min before the initiation and for the duration of the 2-DG procedure. Lumped constants were not affected by hypoxia at any age. At P10, the exposure to the hypoxic gas mixture induced a generalized increase in LCMRglc which affected 41 structures of the 45 studied. At P14, average cerebral glucose utilization was similar in hypoxic and control rats. LCMRglc increased in 5 areas and decreased in 11 regions, mainly brainstem and respiratory areas in hypoxic rats. Finally, at P21, LCMRglc decreased in 11 structures of hypoxic rats. The increase in LCMRglc in the hypoxic 10-day-old rat likely reflects stimulation of anaerobic glycolysis. Conversely, at P14 and P21, when the brain has become more dependent upon oxygen supply for its energy metabolism, levels of LCMRglc are similar in both groups of animals or decreased in a few structures of hypoxic compared to normoxic rats. The results of the present study show that the immature brain responds to an acute hypoxic insult in a specific way according to its maturational state. They are also in good accordance with the higher resistance of the immature animal to oxygen deprivation.

Acute Disease↗

PubMed1992

Quantitative histochemical changes in enzymes involved in energy metabolism in the rat brain during postnatal development. II. Glucose-6-phosphate dehydrogenase and beta-hydroxybutyrate dehydrogenase.

The postnatal maturation of glucose-6-phosphate and beta-hydroxybutyrate dehydrogenase activity was assessed by histochemistry in rats at eight postnatal stages, P0, P5, P10, P14, P17, P21, P35 and the adult stage. Enzyme activities were revealed on cryostat brain sections with nitroblue tetrazolium. Both enzyme activities were low and homogeneous at birth, and increased to reach a peak in all areas studied, at P17 for beta-hydroxybutyrate dehydrogenase and at P21 for glucose-6-phosphate dehydrogenase. Then, glucose-6-phosphate dehydrogenase activity decreased regularly by 20-49% from P21 to adult stage, except in cerebellar white matter where activity did not change after P21. beta-hydroxybutyrate dehydrogenase activity decreased regularly from P17 to adult stage in globus pallidus, hippocampus, thalamus, brainstem, genu of corpus callosum and cerebellar white matter. It sensorimotor cortex, medial geniculate body, caudate nucleus, hypothalamus and inferior colliculus, beta-hydroxybutyrate dehydrogenase activity stayed stable between P17 and P35 and decreased thereafter to adult levels. Finally, in parietal, auditory and cerebellar cortices, beta-hydroxybutyrate dehydrogenase activity either stayed stable or slightly increased after P17. The present study shows that there is a quite good correlation between postnatal changes in cerebral glucose-6-phosphate and beta-hydroxybutyrate dehydrogenase activities and the importance of pentose phosphate pathway and ketone body utilization in the developing brain. Our results also reflect the regional heterogeneity of beta-hydroxybutyrate utilization in the adult rat brain, translating into a remaining high activity of beta-hydroxybutyrate dehydrogenase in cerebral cortex.

Aging↗

PubMed1991

Quantitative histochemical changes in enzymes involved in energy metabolism in the rat brain during postnatal development. I. Cytochrome oxidase and lactate dehydrogenase.

The postnatal maturation of cytochrome oxidase and lactate dehydrogenase activity was assessed by histochemistry in rats at 8 postnatal stages, P0, P5, P10, P14, P17, P21, P35 and the adult stage. Enzyme activities were revealed on cryostat brain sections with diaminobenzidine for cytochrome oxidase and nitroblue tetrazolium for lactate dehydrogenase. Lactate dehydrogenase activity remained unchanged between P0 and P10, significantly increased in 8 areas of the 14 studied between P10 and P14 and in 6 structures from P14 to P17. These were mainly parietal, auditory and cerebellar cortices, hippocampus, thalamus, hypothalamus and medial geniculate body. There was no further change until P35 and lactate dehydrogenase activity increased then significantly to reach higher adult levels in hippocampus and medial geniculate body. Cytochrome oxidase activity was low from P0 to P10 and increased in 8 regions between P10 and P14. These were all cortices, caudate nucleus, hippocampus, inferior colliculus and genu. Enzyme activity further increased between P14 and P17 in auditory cortex, medial geniculate body and brainstem, did not vary from P17 to P21 but increased by 92 to 371% in all areas between P21 and P35. Cytochrome oxidase activity rose further from P35 to adult stage in hippocampus and medial geniculate body. From birth to adulthood, cytochrome oxidase activity increased 5 to 19 fold and lactate dehydrogenase activity 1.8 to 3.0. The present study shows that there is a quite good correlation between postnatal changes in regional cerebral glucose utilization and activity of enzymes involved in glycolytic and oxidative glucose metabolism in the rat.

Aging↗