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M Chalfie

Publications and source records attributed to M Chalfie.

11 recordsLinked to original sources
PubMed1992

Regulation of the mec-3 gene by the C.elegans homeoproteins UNC-86 and MEC-3.

The mec-3 gene encodes a homeodomain protein with LIM repeats that is required for the specification of touch cell fate in Caenorhabditis elegans. Previous experiments suggested that mec-3 expression requires the product of the unc-86 gene, a POU-type homeoprotein, and mec-3 itself. We have analyzed the control of mec-3 expression by identifying potential cis regulatory elements in the mec-3 gene (by conservation in a related nematode and by DNase I footprinting using unc-86 and mec-3 proteins) and testing their importance by transforming C.elegans with mec-3lacZ fusions in which these sites have been mutagenized in vitro. Both unc-86 and mec-3 proteins bind specifically to the promoter of the mec-3 gene, suggesting that both proteins may be directly involved in the regulation of the mec-3 gene. In addition, the footprint pattern with mec-3 protein is altered in the presence of unc-86 protein. In vivo transformation experiments reveal that some of the binding regions of the two proteins are needed for general positive control and maintenance of mec-3 expression while others have no detectable, unique function. Interestingly, the unc-86 gene appears to be required not only to initiate mec-3 expression but also to maintain it.

Amino Acid Sequence↗
PubMed1992

Developmental and abnormal cell death in C. elegans.

Genetic analysis in Caenorhabditis elegans has identified several genes that function in normal developmental death as well as genes that can mutate to cause inappropriate cell death. The processes whereby some of these abnormal deaths occur depend on genes that participate in normal programmed cell death; others occur by an independent mechanism whereby mutation of members of a gene family leads to cell lysis. Molecular characterization of these 'death' genes in C. elegans is beginning to provide insight into the normal and aberrant mechanisms of cell death.

Animals↗
PubMed1991

The mec-4 gene is a member of a family of Caenorhabditis elegans genes that can mutate to induce neuronal degeneration.

Three dominant mutations of mec-4, a gene needed for mechanosensation, cause the touch-receptor neurons of Caenorhabditis elegans to degenerate. With deg-1, another C. elegans gene that can mutate to induce neuronal degeneration and that is similar in sequence, mec-4 defines a new gene family. Cross-hybridizing sequences are detectable in other species, raising the possibility that degenerative conditions in other organisms may be caused by mutations in similar genes. All three dominant mec-4 mutations affect the same amino acid. Effects of amino-acid substitutions at this position suggest that steric hindrance may induce the degenerative state.

Amino Acid Sequence↗
PubMed1979

Organization of neuronal microtubules in the nematode Caenorhabditis elegans.

We have studied the organization of microtubules in neurons of the nematode Caenorhabditis elegans. Six neurons, which we call the microtubule cells, contain bundles of darkly staining microtubules which can be followed easily in serial-section electron micrographs. Reconstruction of individual microtubules in these cells indicate that most, if not all, microtubules are short compared with the length of the cell process. Average microtubule length varies characteristically with cell type. The arrangement of microtubules gives an overall polarity to each bundle: the distal ends of the microtubles are on the outside of the bundle, whereas the proximal ends are preferentially inside. The distal and proximal ends each have a characteristic appearance indicating that these microtubules may have a polarity of their own. Short microtubules in processes of other neurons in C. elegans have also been observed.

Animals↗
PubMed1977

Catecholamine release from the adrenal medulla.

Chromaffin cells in the adrenal medulla are specialized for the synthesis, storage, and secretion of catecholamines. These cells are innervated by preganglionic sympathetic neurons in the splanchnic nerves, and, because of their unique blood supply, are exposed to unusually high concentrations of glucocorticoids in the venous drainage from the adrenal cortex. Splanchnic nerve stimulation appears to be the most important determinant of adrenomedullary function. Chromaffin cells synthesize catecholamines from tyrosine. Splanchnic nerve stimulation leads to an increase in the activity of several of the catecholamine biosynthetic enzymes, and to an increase in the rate of catecholamine biosynthesis. Glucocorticoids cause the induction of the enzyme noradrenaline N-methyltransferase, and so are particularly important for the synthesis of epinephrine. Catecholamines are stored, together with ATP, Ca2+, and protein, in secretory vesicles known as chromaffin granules. Splanchnic nerve stimulation is the physiological stimulus for catecholamine secretion. Stimulation of the splanchnic nerves results in the release of ACh from nerve endings in the adrenal medulla. ACh causes an increase in the permeability of the chromaffin cells to Ca2+, and thereby leads to the entry of Ca2+ into the cells. Ca2+ then causes the secretion of catecholamines and of other chromaffin granule constituents from the chromaffin cells by exocytosis. The biochemical mechanisms of exocytosis, and the mechanism by which Ca2+ stimulates this process, are still unknown.

Acetylcholine↗
PubMed1977

Regulation of catecholamine biosynthesis in a transplantable rat pheochromocytoma.

Cells prepared from a transplantable rat pheochromocytoma synthesize norepinephrine from 14C-tyrosine, at a rate of 9.4 +/- 0.5 pml/min/mg of protein, in vitro. Incubation of the cells in a medium containing 56 mM K+ results in a 2- to 6-fold increase in norepinephrine synthesis. This increase in norepinephrine synthesis is dependent upon the presence of Ca++ in the incubation medium. Stimulation of the cells by 56 mM K+ increases the conversion of tyrosine to dopa in the presence of brocresine (an inhibitor of aromatic L-amino acid decarboxylase), and has no effect on the conversion of 3H-dopa to norepinephrine. Cells can be depleted of up to 70% of their catecholamine stores by prior incubation in 56 mM K+. Norepinephrine synthesis in catecholamine-depleted cells incubated under control conditions in only slightly (20-40%) greater than it is in nondepleted cells. However, 56 mM K+ PRODUCES A SIMILAR INCREASE IN NOREPINEPHRINE SYNTHESIS IN DEPLETED CELLS AS IT DOES IN NONDEPLETED CELLS. Inhibition of amine oxidase (flavin containing) by preincubaiton with pargyline does not greatly affect catecholamine synthesis. Incubation of the cells in 56 mMK+ results in an increase in tyrosine 3-monooxygenase activity. These results indicate that the depletion of catecholamine stores plays only a minor role in the increase in norepinephrine synthesis caused by the stimulation of chromaffin cells and suggest that the activation of tyrosine 3-monooxygenase plays a more important role in this phenomenon.

Animals↗
PubMed1976

Studies of a transplantable rat pheochromocytoma: biochemical characterization and catecholamine secretion.

The biochemistry and secretory characteristics of a transplantable rat pheochromocytoma have been studied. This tumor possesses the enzyme required for the biosynthesis of norepinephrine from tyrosine, and stores large amounts of norepinephrine (33 +/- 3 nmol/mg of protein). The tumor does not have detectable levels of noradrenalin N-methyltransferase, nor does it contain significant amounts of epinephrine. Approximately two-thirds of the catecholamine content, and one-half of the dopamine beta-monoxygenase activity in the tumor can be isolated in a granule fraction by sedimentation. This granule fraction also contains ATP; the molar ratio of catecholamine to ATP in this granule fraction (5.6 +/- 0.9) is similar to that found in granules prepared from normal adrenal glands. Cell suspensions were prepared by mechanical disruption of the tumor. Incubation of these cell suspensions in media containing 56 mM K+, or the divalant cation ionophores, lasolocid or A23187, leads to the release of catecholamine from these cells. The cells do not secrete catecholamine in response to acetycholine. Catecholamine release induced by 56 mM K+ appears to be by exocytosis, since this release is dependent upon extracellular Ca++, and is accompanied by the release of dopamine beta-monooxygenase, but not of lactate dehydrogenase, from the cells. The mechanism by which the ionophores stimulate catecholamine secretion has not been established.

Adenosine Triphosphate↗