Biomedical subjects

D R Caprette

Publications and source records attributed to D R Caprette.

6 recordsLinked to original sources

PubMed2001

Control of Drosophila perineurial glial growth by interacting neurotransmitter-mediated signaling pathways.

Drosophila peripheral nerves, similar structurally to the peripheral nerves of mammals, comprise a layer of axons and inner glia, surrounded by an outer perineurial glial layer. Although it is well established that intercellular communication occurs among cells within peripheral nerves, the signaling pathways used and the effects of this signaling on nerve structure and function remain incompletely understood. Here we demonstrate with genetic methods that the Drosophila peripheral nerve is a favorable system for the study of intercellular signaling. We show that growth of the perineurial glia is controlled by interactions among five genes: ine, which encodes a putative neurotransmitter transporter; eag, which encodes a potassium channel; push, which encodes a large, Zn(2+)-finger-containing protein; amn, which encodes a putative neuropeptide related to the pituitary adenylate cyclase activator peptide; and NF1, the Drosophila ortholog of the human gene responsible for type 1 neurofibromatosis. In other Drosophila systems, push and NF1 are required for signaling pathways mediated by Amn or the pituitary adenylate cyclase activator peptide. Our results support a model in which the Amn neuropeptide, acting through Push and NF1, inhibits perineurial glial growth, whereas the substrate neurotransmitter of Ine promotes perineurial glial growth. Defective intercellular signaling within peripheral nerves might underlie the formation of neurofibromas, the hallmark of neurofibromatosis.

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PubMed2000

A protein containing a serine-rich domain with vesicle fusing properties mediates cell cycle-dependent cytosolic pH regulation.

Initial differentiation in Dictyostelium involves both asymmetric cell division and a cell cycle-dependent mechanism. We previously identified a gene, rtoA, which when disrupted randomizes the cell cycle-dependent mechanism without affecting either the underlying cell cycle or asymmetric differentiation. We find that in wild-type cells, RtoA levels vary during the cell cycle. Cytosolic pH, which normally varies with the cell cycle, is randomized in rtoA cells. The middle 60% of the RtoA protein is 10 tandem repeats of an 11 peptide-long serine-rich motif, which we find has a random coil structure. This domain catalyzes the fusion of phospholipid vesicles in vitro. Conversely, rtoA cells have a defect in the fusion of endocytic vesicles. They also have a decreased exocytosis rate, a decreased pH of endocytic/exocytic vesicles, and an increased average cytosolic pH. Our data indicate that the serine-rich domain of RtoA can mediate membrane fusion and that RtoA can increase the rate of vesicle fusion during processing of endoctyic vesicles. We hypothesize that RtoA modulates initial cell type choice by linking vegetative cell physiology to the cell cycle.

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PubMed2000

A precise group size in Dictyostelium is generated by a cell-counting factor modulating cell-cell adhesion.

A remarkable aspect of Dictyostelium development is that cells form evenly sized groups of approximately 2 x 10(4) cells. A secreted 450 kDa protein complex called counting factor (CF) regulates the number of cells per group. We find that CF regulates group size by repressing cell-cell adhesion. In both experiments and computer simulations, high levels of CF (and thus low adhesion) result in aggregation streams breaking up into small groups, while no CF (and thus high adhesion) results in no stream breakup and large groups. These results suggest that in Dictyostelium and possibly other systems a secreted factor regulating cell-cell adhesion can regulate the size of a group of cells.

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PubMed1994

Different temporal patterns of expression result in the same type, amount, and distribution of filamin (ABP) in cardiac and skeletal myofibrils.

The morphogenesis of functional myofibrils in chick skeletal and cardiac muscle occurs in greatly different time spans, in about 7 and 2 days, respectively. In chick skeletal myogenic cells, one isoform of the 250 kD actin-binding protein (ABP) filamin is associated with stress fiber-like structures of myoblasts and early myotubes, then disappears for approximately 4 days, whereupon a second filamin isoform reappears at the Z-disc periphery. We sought to determine if cardiac myogenesis involves this sequence of appearance, disappearance, and reappearance of a new filamin isoform in a compressed time scale. It was known that in mature heart, filamin is localized at the Z-disc periphery as in mature (fast) skeletal muscle, and is also associated with intercalated discs. We find that myocardial filamin has an apparent molecular weight similar to that of adult skeletal muscle filamin and lower than that of smooth muscle filamin, and that both skeletal and cardiac muscle contain roughly 200 filamin monomers per sarcomere. Two-dimensional peptide mapping shows that myocardial filamin is very similar to skeletal muscle filamin. Myocardial, slow skeletal, and fast skeletal muscle filamins are all phosphorylated, as previously shown for filamin of non-striated muscle. Using immunofluorescence, we found that filamin could not be detected in the developing heart until the 14-somite stage, when functional myofibrils exist and the heart has been beating for 3 to 4 hours. We conclude that in cardiac and skeletal myogenesis, different sequences of filamin gene expression result in myofibrils with similar filamin distributions and isoforms.

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PubMed1986

Association of clathrin with microsomes isolated from canine myocardium.

We and others have observed specialized regions of sarcoplasmic reticulum membranes that resemble coated vesicles, in the I-band region of myocardial cells. These structures have been named "corbular" sarcoplasmic reticulum, and are distinct in appearance from Golgi-associated coated vesicles, in that they are larger and contain a flocculent material that has been identified as calsequestrin. Whereas it has been suggested that these structures have a role in cardiac calcium metabolism, their function(s) and the molecular identity of the characteristic "bristle" coat remain unknown. Microsomes enriched in sarcoplasmic reticulum were prepared from canine ventricular muscle by Polytron homogenization in pH 6.5 buffer, followed by differential centrifugation. Protein was released by incubation in 50 mM Tris/HCl, pH 8, followed by centrifugation. We found these extracts to be enriched in a protein that was identical to brain clathrin in mobility on a Sepharose 4B gel filtration column, final position of the native protein following nondenaturing electrophoresis, relative mobility in denaturing (sodium dodecyl sulfate) electrophoresis on 6% and 7.5% gels, and antigenicity to anti-clathrin IgG. These findings confirmed the presence of clathrin triskelions in the cardiac microsome extract. On this basis, we suggest that clathrin may be a component of the electron dense "coat" of corbular sarcoplasmic reticulum.

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PubMed1984

Isovolumetric performance of isolated ground squirrel and rat hearts at low temperature.

The effects of low temperature on mechanical performance of the isolated left ventricles of the 13-lined ground squirrel (a hibernator) and the rat (a nonhibernator) were studied. In addition, low-temperature performance of hearts from summer-active, winter-hibernating, and winter-active ground squirrels were compared. By measuring pressure (P) generated against a balloon inserted into the left ventricle, maximum developed pressure (DP) and maximum rate of increase of P (peak dP/dt) were determined over a temperature range of 5-20 degrees C. The DP and dP/dt of the rat ventricle exhibited significantly greater reduction in magnitude at reduced temperature, compared with those of ground squirrel ventricle. Rat, but not ground squirrel, hearts exhibited arrhythmias of various kinds, including extra-systoles, tachycardia, pulsus alternans, and periods of asystole. Hearts from winter-active ground squirrels developed greater pressures than those from winter-hibernating and summer-active animals. This evidence suggests that disruption of cell communication in the nonhibernator ventricular myocardium plays an important role in the failure of the nonhibernator heart at low body temperatures. Contractility of the seasonal hibernator's heart is influenced by both season and hibernation itself, possibly through shifts in myocardial metabolism. However, seasonal adaptations appear not to be required to confer the special resistance of the seasonal hibernator's heart to the deleterious effects of low temperature.

Acclimatization↗