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F Wohlrab

Publications and source records attributed to F Wohlrab.

At least 19 recordsLinked to original sources
PubMed2000

The major chicken egg envelope protein ZP1 is different from ZPB and is synthesized in the liver.

The extracellular matrix surrounding vertebrate oocytes is called the zona pellucida in mammals and perivitelline membrane (pvm) in birds. We have analyzed this structure in chicken follicles and laid eggs and have identified a 95-kDa component of the pvm, which, by protein sequencing, shows homology to mammalian zona pellucida proteins. Surprisingly, we could not detect this protein in ovarian granulosa cells or oocytes but instead found high levels in the liver of the laying hen. In contrast, it is absent in rooster liver but can be efficiently induced by estrogen treatment of the animal. An immunoscreen of a liver lambda-ZAP library yielded a cDNA coding for a protein of 934 amino acids. It displayed significant homology to members of the ZP1/ZPB family from other species, notably to mouse and rat ZP1, and was therefore designated chkZP1. It is clearly different from a protein designated chkZPB that had been deposited in the data base previously. Alignment of the known members of the ZP1/ZPB family demonstrated the existence of at least three subgroups, with representatives of both the ZP1 and the ZPB sequence homology group occurring in vertebrates. Northern blot analysis of liver extracts revealed the presence of a single 3. 2-kilobase mRNA coding for chkZP1, distinct from the chkZPB transcript detectable in follicles. Immunohistochemical analysis of follicle sections demonstrates that chkZP1 can be found in the blood vessels of the theca cell layer as well as in the pvm surrounding the oocyte. Thus, in the chicken, at least one of the major pvm components is synthesized in the liver and is transported via the bloodstream to the follicle.

Amino Acid Sequence↗
PubMed2000

Islet graft-induced changes of beta-hydroxybutyrate dehydrogenase and glucose-6-phosphatase activity in liver cells of diabetic recipient rats.

It is known that the liver is a favourable site for implantation of pancreatic islets since the grafted islets remain metabolically intact and provide long-term normoglycemia in diabetic animals. However, the long-term effects exerted by the grafted tissue on the host organ are not well defined. We therefore investigated by light and electron microscopy the effects of syngeneic islets on the host organ after intraportal transplantation into the liver of streptozotocin (STZ)-induced diabetic LEW.1W rats. In addition, tissue sections of graft-bearing liver were stained by enzyme histochemical methods for beta-hydroxybutyrate dehydrogenase (HBDH) and glucose-6-phosphatase (G6Pase). At 12 weeks after transplantation, the changes seen in the hepatocytes surrounding the grafted islets were hyperproliferation and accumulation of glycogen. Hepatocytes adjacent to the implanted islets displayed increased HBDH activity, whereas G6Pase activity was variable, either decreased or increased. Increased HBDH activity was also observed in the periportal region and in liver cells extending to the central veins. The results demonstrate that intraportal islet grafts, in addition to normalizing glucose homeostasis, exert remarkable effects on the liver parenchyma of experimentally diabetic recipient rats.

Animals↗
PubMed1998

Molecular cloning and expression of an avian rab5 homolog.

A chicken rab5 cDNA was isolated that contains the complete open reading frame for a protein of 216 amino acids, which, by comparison with available rab5 sequences from other species, is most closely related to the rab5c isoform. Two rab5 transcripts of 1.3 and 1.8 kb were detectable in various chicken tissues; they are abundant in tissues with high endocytic activity, such as brain, ovary, and testis. Similarly, high levels of rab5 protein expression were found in endocytotically active tissues and were increased upon estrogen treatment of roosters.

Amino Acid Sequence↗
PubMed1997

Glucose transporter isoform (GLUT) 2 expression in beta-cells of long-term syngeneic islet grafts.

Syngeneic islets were transplanted into the liver of streptozotocin (STZ)-induced diabetic LEW.1W rats, and the expression of the glucose transporter isoform GLUT 2, an essential component of the glucose-sensing mechanism of the pancreatic beta-cell, was determined in the grafted islet tissue. Graft-bearing liver was obtained 12, 36, and 60 weeks after transplantation, and tissue sections were immunoperoxidase stained for GLUT 2 and major islet peptides. Islet cell aggregates of different sizes were found in the portal tract and in juxtaposition to the hepatocytes. At all time points, beta-cells in the grafts displayed GLUT 2 expression comparable to that of islets in nondiabetic rats. Islet cells containing immunoreactive insulin and islet amyloid polypeptide were plentiful, while those staining positive for glucagon and somatostatin were scarce in these grafts. The results show that beta-cells in islets engrafted in the liver, although initially exposed to chronic hyperglycemia, have the capability of stably expressing GLUT 2 over long-term periods.

Animals↗
PubMed1995

Development of A-type (axonless) horizontal cells in the rabbit retina.

The development of A-type horizontal cells (HC) was studied in the rabbit retina between embryonic day (E)24 and adulthood [the day of birth was called postnatal day (P)1 and corresponds to E31-32]. The cells were visualized by several methods 1) by immunolabeling with antibodies to neurofilament 70,000 (NF-70kD), 2) by immunolabeling with antibodies to a calcium binding protein (CaBP-28kD), 3) by two different methods of silver impregnation, and 4) by histochemical demonstration of NADH-diaphorase activity. Most methods labeled A-type HC only in the dorsal retina; thus, our study is restricted to HC of this region. HC densities were determined at each developmental stage. The cells were drawn at scale, and size, quotient of symmetry, and topographical orientation of dendritic trees were studied by image analysis. The growth of HC dendritic fields was correlated with data on the postnatal local retinal expansion, which is known to be driven by the intraocular pressure (after cessation of retinal cell proliferation at P9). This expansion was evaluated in an earlier paper (Reichenbach et al. [1993] Vis. Neurosci. 10:479-498) by using local subpopulations of Müller cells as "markers" of distinct topographic regions of the retinae. After E24, when the final number of HC is established, we can discriminate three distinct developmental stages of A-type HC. During the first stage, between E24 and E27, the young cells are often vertically oriented and may extend their first short dendrites within (the primordia of) both plexiform layers. The irregular HC mosaic at E24 shows a significant difference to all other stages. The second stage begins after birth when the dendritic trees of the cells are already restricted to the outer plexiform layer. Between P3 and P9, their dendritic trees enlarge more than the surrounding retinal tissue expands, and the coverage factor almost doubles from 2.5 to 4.4. The third stage occurs after P9 when the growth rate of dendritic tree areas corresponds to that of the local retinal tissue expansion caused by "passive stretching" of the postmitotic tissue, and the coverage factor remains constant. This is compatible with the view that mature synaptic connections of A-type HC are mostly established after the first week of life and are then maintained.

Animals↗
PubMed1995

Differential effects of simple repeating DNA sequences on gene expression from the SV40 early promoter.

The influence of simple repeat sequences, cloned into different positions relative to the SV40 early promoter/enhancer, on the transient expression of the chloramphenicol acetyltransferase (CAT) gene was investigated. Insertion of (G)29.(C)29 in either orientation into the 5'-untranslated region of the CAT gene reduced expression in CV-1 cells 50-100 fold when compared with controls with random sequence inserts. Analysis of CAT-specific mRNA levels demonstrated that the effect was due to a reduction of CAT mRNA production rather than to posttranscriptional events. In contrast, insertion of the same insert in either orientation upstream of the promoter-enhancer or downstream of the gene stimulated gene expression 2-3-fold. These effects could be reversed by cotransfection of a competitor plasmid carrying (G)25.(C)25 sequences. The results suggest that a G.C-binding transcription factor modulates gene expression in this system and that promoter strength can be regulated by providing protein-binding sites in trans. Although constructs containing longer tracts of alternating (C-G), (T-G), or (A-T) sequences inhibited CAT expression when inserted in the 5'-untranslated region of the CAT gene, the amount of CAT mRNA was unaffected. Hence, these inhibitions must be due to posttranscriptional events, presumably at the level of translation. These effects of microsatellite sequences on gene expression are discussed with respect to recent data on related simple repeat sequences which cause several human genetic diseases.

Animals↗
PubMed1995

Reinnervation of pancreatic islets and regulation of insulin secretion by hepatic sympathetic nerves after intraportal transplantation of islets into livers of diabetic rats.

It was the aim of this study to elucidate whether intraportally transplanted pancreatic islets were reinnervated after transplantation and whether the secretion of insulin from pancreatic islets might be modulated by the vegetative innervation of recipient livers. Two weeks after intraportal transplantation of 2000 neonatal pancreatic islets recipient rats completely recovered from streptozotocin-induced diabetes. Predominantly catecholaminergic, but also cholinergic nerve fibers were detected in islet cell complexes between beta-cells. Corresponding electron micrographs showed beta-cells in close contact with axons of nonmyelinated nerve fibers. Perfusion studies with livers of recipient rats revealed that the inhibition by hepatic sympathetic nerves of insulin secretion was mediated via alpha 2-receptors as in normal pancreatic islets.

Animals↗
PubMed1994

Intraportal transplantation of pancreatic islets into livers of diabetic rats. Reinnervation of islets and regulation of insulin secretion by the hepatic sympathetic nerves.

Two weeks after intraportal transplantation of 2,000 neonatal pancreatic islets, recipient rats completely recovered from streptozotocin-induced diabetes. The reversal of diabetes could be documented by the normalization of blood glucose levels, by a restored weight gain, by normal glucagon and insulin levels in blood, and by a disappearance of polyuria and polydipsia. The reversal remained stable for at least 9 months. This study determined whether intraportally transplanted pancreatic islets were reinnervated after transplantation and whether the secretion of insulin and glucagon from pancreatic islets might be modulated by the vegetative innervation of recipient livers. Predominantly catecholaminergic but also cholinergic nerve fibers were detected not only within the portal tracts around hepatic arteries, portal veins, and bile ducts, but also at the borderline of hepatocytes and beta-cells and in islet cell complexes between beta-cells. Corresponding electron micrographs showed beta-cells in close contact with axons of nonmyelinated nerve fibers. Isolated livers were single pass perfused via both the hepatic artery and the portal vein. An increase in glucose level from 5 to 14 mmol/l enhanced hepatic glucose uptake and increased insulin secretion from transplanted islets with a biphasic secretion profile but had no effect on glucagon output. Stimulation of the nerve plexus around the hepatic artery and the portal vein (7.5 Hz, 2 min), which activates primarily the sympathetic system, not only reduced glucose uptake and perfusion flow but also completely reversed the glucose-stimulated increase in insulin secretion. Nerve stimulation did not influence glucagon secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

GC-rich flanking tracts decrease the kinetics of intramolecular DNA triplex formation.

The effect of the base composition of flanking sequences on DNA intramolecular triplex formation was investigated in negatively supercoiled plasmids. The rates of triplex formation at two oligopurine.oligopyrimidine inserts with interrupting sequences in plasmids containing AT- or GC-rich flanking sequences were compared as a function of temperature, pH, and negative superhelical density. The kinetics of the transition of linear B-DNA to triplex (also called H-DNA) were influenced by all of these factors; triplexes were formed slower in a GC-rich background than in an AT-rich background. However, at equilibrium, the same amounts of the triplexes in AT- or GC-rich contexts were formed, and the conformations adopted by (GAA)4TTCGC(GAA)4 showed the canonical intramolecular triplex as mapped with chemical probes. We propose that the GC-rich segments caused this effect by thermodynamically clamping the DNA inserts, since the dependence of kinetics on base composition disappeared in tetraalkylammonium ions which eliminate the dependence of helix-coil transitions on base composition. The dependence of the kinetics of intramolecular triplex formation on flanking sequences further strengthens the concept of the role of DNA as a dynamic participant in cellular events.

Base Sequence↗
PubMed1992

Metal ions cause the isomerization of certain intramolecular triplexes.

The influence of cations on the capacity of five oligopurine.oligopyrimidine mirror repeat sequences to adopt intramolecular triplexes (the usual H-y3 isomer and/or the rare H-y5 isomer) in recombinant plasmids was investigated. Unexpectedly, the presence of certain metal ions (magnesium, zinc, manganese, and calcium) stabilized the (GAA)4TTCGC(GAA)4 insert in the rare H-y5 when cloned into either of two different sequence backgrounds. Alternatively, either shortening or lengthening the sequence at the central interruption, which becomes the loop of the triplex, led to the formation of the canonical H-y3 under all conditions tested. Similarly, other oligopurine.oligopyrimidine mirror repeat sequences (i.e. (GAA)8 or (GGA)8) formed only the H-y3 under all experimental conditions. All triplexes were stabilized by negative supercoiling at pH 5.0; chemical probe and primer extension analyses served as critical structural tools. Hence, the nature of the central interruption sequence (the loop) of the mirror repeat is important for the stabilization of the H-y5. This region may be important for metal ion binding in the initial stages of triplex formation and thus may play a critical role in determining which isomer is formed. The possible biological role of a DNA sequence adopting three different conformations is discussed.

Cations↗
PubMed1991

The herpes simplex virus 1 segment inversion site is specifically cleaved by a virus-induced nuclear endonuclease.

Nuclear extracts from several tissue culture cell lines (human, primate, and murine) contain an endonuclease that specifically cleaves sequences at the herpes simplex virus 1 (HSV-1) segment inversion site. Mapping studies identified the preferential site of cleavage as a set of tandemly repeated dodecamers, the DR2 repeats. Endonuclease levels vary according to the proliferative state of the cell; little or no activity is detectable in extracts from quiescent cells, whereas high levels are expressed in dividing cells. Also, infection of density-arrested BSC-1 cells with HSV-1 induces a substantial increase (at least 35-fold) in endonucleolytic activity, which is first detectable at about 1 hr after infection at 32 degrees C. The elevated levels of enzyme activity then persist throughout the viral life cycle. In addition to the HSV-1 DR2 repeats, certain other G+C-rich sequences with an asymmetric distribution of purines and pyrimidines on the DNA strands and with appropriate sequences and lengths are substrates for the nuclease. These data indicate that target site recognition by the enzyme is conformation specific rather than sequence specific.

Animals↗
PubMed1991

[Victoria blue: staining properties in orthology and pathology].

The staining properties of the cationic dye Victoria Blue are summarized in consideration of the findings in the literature and own findings. Dependent on the staining conditions (with or without preoxidation of tissue sections), different structures and substances are stained by Victoria Blue. Without preoxidation elastic fibres, acid glycosaminoglycanes and DNA predominantly stained, but with preoxidation the dye stained insulin, some peptide hormones and secretion products, HBs-antigen, and lipofuscin. The chemism of the histochemical reaction is not quite understood yet.

Animals↗
PubMed1990

Morphological findings in the liver of diabetic rats after intraportal transplantation of neonatal isologous pancreatic islets.

Morphological (light microscopical, immunohistological and electron microscopical) findings in the recipient liver of rats with streptozotocin-induced diabetes, obtained 9 months after intraportal injection of neonatal isologous pancreatic islets, are described and their significance discussed. The results support the assumption of active ingrowth of nonmyelinated nerve fibers into the islet isografts. The hepatocytes surrounding the islet isografts contain--obviously owing to the influence of unusually high and locally variable concentrations of insulin--a focally increased number of enlarged mitochondria, abundant glycogen and a smaller amount of neutral fat droplets. Furthermore, hepatocytes and cells looking like hepatocytes (hepatocyte-like cells) with typically structured cytoplasmic beta (insulin) granules were found bordering the islet isografts. These results could be interpreted as an expression of artificial or nonartificial fusion of beta cells with hepatocytes, i.e. formation of hybrid cells ("in vivo hybridization"). Alternatively, they might reflect insulin uptake and storage in the hepatocytes. In addition, these findings suggest that contact between neonatal islet tissue and liver tissue could be a trigger for the in vivo transformation (modulation) of differentiated cells of similar embryonic development in the adult organism.

Animals↗
PubMed1990

[Gomori reactions in orthology and pathology].

The following four basic histochemical reactions were developed by Gomori (1904-1957): 1. Silver impregnation of reticular fibres (1937); 2. Metal salt principle for detection of hydrolytic enzyme activity (1939); 3. Silver-methenamine reaction (1946); 4. Aldehyde fuchsin reaction (1950). These reactions and their modifications have assumed growing importance to expansion of knowledge, primarily on orthological and pathobiological problems.

Histocytochemistry↗
PubMed1990

[Proliferation of beta cells after syngeneic transplantation of isolated Langerhans cells into the spleens of diabetic rats].

Syngeneic transplantation of cultured and functionally characterized neonatal islet into the spleen of streptozotocin diabetic Lewis rats resulted in long time survival up to 200 days and in plasma glucose levels lower than 9 mmol/l. The daily plasma glucose profile of transplanted rats had shown significantly above that of non diabetic control rats. 200 days after transplantation morphologically intact, insulin containing beta-cells were demonstrable in the spleen, thus demonstrating the long-term survival of functioning islet cells. Proliferation of beta-cells was shown in the transplanted islets. In addition, beta-cell clusters were found which derived from pancreatic ductules transplanted together with the isolated islets into the spleen. Mitose were visible within ductular epithelial cells. The proliferative response of islets after intrasplenic transplantation is probably the result of a long-term stimulation by slightly enhanced plasma glucose values of the transplanted acceptors compared to control animals.

Animals↗