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J Jack

Publications and source records attributed to J Jack.

15 recordsLinked to original sources
PubMed1996

The Drosophila insulin receptor is required for normal growth.

Drosophila contain an insulin receptor homologue, encoded by the inr gene located at position 93E4-5 on the third chromosome. The receptor protein is strikingly homologous to the human receptor, exhibiting the same alpha2beta2 subunit structure and containing a ligand- activated tyrosine kinase in its cytoplasmic domain. Chemical mutagenesis was used to induce mutations in the inr gene and six independent mutations that lead to a loss of expression or function of the receptor protein were identified. These mutations are recessive, embryonic, or early larval lethals, but some alleles exhibit heteroallelic complementation to yield adults with a severe developmental delay (10 days), growth-deficiency, female-sterile phenotype. Interestingly, the severity of the mutant phenotype correlates with biochemical measures of loss of function of the receptor tyrosine kinase. The growth deficiency appears to be due to a reduction in cell number, suggesting a role for inr in regulation of cell proliferation during development. The phenotype is reminiscent of those seen in syndromes of insulin-resistance or IGF-I and IGF-I receptor deficiencies in higher organisms, suggesting a conserved function for this growth factor family in the regulation of growth and body size.

Alleles↗
PubMed1995

Structure and regulation of a complex locus: the cut gene of Drosophila.

The cut locus encodes a homeobox protein that is localized in the nuclei of a variety of tissues and is required for proper morphogenesis of those tissues. Cut protein is required in embryonic and adult external sensory organs, where its absence results in conversion of the organs to chordotonal organs. Expression of cut also occurs in the Malpighian tubules, spiracles, central nervous system, and a number of other tissues. Gypsy transposon insertions upstream of the cut promoter block expression in subsets of these tissues. The effect of the gypsy insertions is polar, with those farthest from the promoter affecting the fewest tissues. The hypothesis that gypsy insertions block a series of tissue-specific enhancer elements that are distributed over a region of 80 kb upstream of the promoter predicts the location of the enhancers for cut expression in each of the tissues in which it is active in embryos. DNA fragments from this region drive expression of a reporter gene in each of the embryonic tissues in which endogenous cut gene is expressed. Each tissue has its own enhancer, and none of the enhancers require the activity of the endogenous cut gene to function.

Animals↗
PubMed1992

Presynaptic release probability influences the locus of long-term potentiation.

The quantal hypothesis proposes that chemical synaptic transmission involves the probabilistic release of multimolecular packets of transmitter. Analysis of the resulting trial-to-trial fluctuations in postsynaptic response can provide estimates both of the number of quanta released and of the size of their postsynaptic effect. This in turn permits the quantification of the relative contributions of pre- and postsynaptic factors to the strength of a given synapse. Quantal analysis of excitatory synapses in the hippocampus has proved difficult and has led to contradictory conclusions when applied to long-term potentiation. Here we report the use of a combination of quantal analysis procedures to provide evidence that both pre- and postsynaptic changes can contribute substantially to the maintenance of long-term potentiation in the CA1 region of the hippocampus. The initial setting of the presynaptic release mechanism seems to determine their relative importance.

Animals↗
PubMed1992

Regulatory interactions and role in cell type specification of the Malpighian tubules by the cut, Krüppel, and caudal genes of Drosophila.

Krüppel and caudal genes are both required for normal segmentation of the embryo, and the developmental regulatory gene cut is necessary for the normal specification of external sensory organs. These three genes are also expressed in the Malpighian tubules before and during differentiation. Two of the genes, Krüppel and cut, are known to be required for development of the tubules. We report that the absence of maternal and zygotic caudal function reduces their normal growth and elongation. Normal Krüppel function, which is known to be required for caudal expression, is also required for cut expression, while cut and caudal are expressed independently of each other. Cell type transformations of Malpighian tubules were studied by examining the effects of mutations on the expression of markers specific to Malpighian tubules, hindgut, or midgut of normal embryos. Loss of Krüppel activity confers hindgut characteristics on those cells that normally form the Malpighian tubules with all markers tested. Loss of cut function alters the expression of some markers but not others. The pathway of tissue specific gene regulation, apparently, branches beyond Krüppel to form at least a cut and a caudal branch.

Animals↗
PubMed1992

Effect of wing scalloping mutations on cut expression and sense organ differentiation in the Drosophila wing margin.

A number of wing scalloping mutations have been examined to determine their effects on the mutant phenotype of cut mutations and on the expression of the Cut protein. The mutations fall into two broad classes, those which interact synergistically with weak cut wing mutations to produce a more extreme wing phenotype than either mutation alone and those that have a simple additive effect with weak cut wing mutations. The synergistically interacting mutations are alleles of the Notch, Serrate and scalloped genes. These mutations affect development of the wing margin in a manner similar to the cut wing mutations. The mutations inactivate the cut transcriptional enhancer for the wing margin mechanoreceptors and noninnervated bristles and prevent differentiation of the organs. Surprisingly, reduction of Notch activity in the wing margin does not have the effect of converting epidermal cells to a neural fate as it does in other tissues of ectodermal origin. Rather, it prevents the differentiation of the wing margin mechanoreceptors and noninnervated bristles.

Alleles↗
PubMed1991

Quantal analysis of excitatory synaptic action and depression in hippocampal slices.

Quantal analysis can provide a quantitative description of important aspects of chemical synaptic transmission and its modification. The technique has recently been applied to excitatory synapses within the hippocampus, especially the form of synaptic plasticity known as long-term potentiation. However, these attempts have met with only limited success, in that the individual quantal amplitudes making up the synaptic response generally could not be resolved. Here we have paid attention to the possible instability of the quantal fluctuation pattern over time. We were able to resolve individual quantal component amplitudes for a high proportion of the experiments, and so demonstrate the quantal nature of excitatory transmission in the CA1 region of the hippocampus. Mean quantal amplitudes for individual excitatory postsynaptic potentials were 84-197 microV, with a mean of 131 +/- 29 microV. For periods during which the fluctuation pattern was stable, the variance associated with individual quantal amplitudes was low. We have also used quantal analysis to show that synaptic depression following prolonged stimulation at these synapses is primarily a presynaptic phenomenon.

Analysis of Variance↗
PubMed1991

Retinal axons in Xenopus show different behaviour patterns on various glial substrates in vitro.

Several lines of evidence suggest that glial cells have major effects on neuronal pathfinding. We have examined in vitro whether the outgrowth pattern of Xenopus retinal fibres is influenced by the glial cells encountered as they grow to the optic tectum. Strips of retina were cultured on monolayers of glial cells from the diencephalon and from the rostral and caudal ends of the optic tectum. On glia from the caudal end of the tectum the growth of fibres from the nasal and temporal ends of the strips was different: temporal fibres were shorter and more fasciculated than nasal fibres. This difference was still discernible on glia isolated from the rostral end of the tectum, but to a lesser extent. On glia from the diencephalon there was no difference between nasal and temporal fibres.

Animals↗
PubMed1991

Four distinct regulatory regions of the cut locus and their effect on cell type specification in Drosophila.

The cut gene in Drosophila is necessary in at least one cell type, the external sensory organs, for proper cell type specification and morphogenesis. It is also expressed in a variety of other tissues, where its function is less well characterized. Previous work has demonstrated that mutations affecting all the tissues map in the transcribed and translated portion of the gene, while mutations that are tissue specific in their effects map in the 140 kb upstream of the most 5' exon known. Within that 140 kb, the mutations fall into four subregions, two of which contain mutations affecting unique sets of tissues and the other two of which contain mutations that affect a third set. Our examination of the defects of mutants, their complementation behavior, and their effect on the distribution of the cut protein in embryos, alters the picture in three important ways. First, some mutations convert the cells of the Malpighian tubules into what appear to be gut cells, suggesting that cut is necessary for cell type specification and morphogenesis in a variety of tissues. Second, mutations in each of the four subregions in the 140 kb of upstream DNA cause a different set of phenotypes, suggesting that the regulatory region contains at least four separate units with different tissue specific functions. And third, mutations have now been identified that map in the transcribed and translated portion of the gene but that have tissue specific effects.

Alleles↗
PubMed1991

Expression of the cut locus in the Drosophila wing margin is required for cell type specification and is regulated by a distant enhancer.

The cut locus is a complex gene whose function is necessary for specification of a number of cell types, including the external sensory organs. The cut wing class of mutations of the cut locus are homozygous viable and lack tissue from the wing margin, which is normally composed of external sensory organs and noninnervated bristles. Expression of cut was examined in the developing wings of wild-type and mutant pupae using an antiserum against Cut protein. Cut is expressed in all of the external sensory organs of the wing and the noninnervated bristles of the posterior margin. The cut wing class of mutations prevents Cut expression specifically in the wing margin mechanoreceptors and noninnervated bristles, apparently preventing neural differentiation. The transformed cells die soon after differentiation would have occurred. We identify an enhancer, located about 80 kb upstream of the cut gene promoter, that confers expression in the cells of the mechanoreceptors and noninnervated bristles from a heterologous promoter. The 27 gypsy retrotransposon insertions that prevent expression in these margin cells, all occur between this enhancer and the promoter. These gypsy insertions probably interfere with the interaction between the enhancer and the cut gene promoter.

Animals↗
PubMed1986

Bier's block--an improved technique.

A simple modification to the method of regional anaesthesia known as Bier's block is presented. This was applied to patients with Colles' fractures. In a controlled trial the technique produced anaesthesia more quickly than the other method.

Anesthesia, Conduction↗
PubMed1985

The penetration of detergents into adult and infant eyes: possible hazards of additives to ophthalmic preparations.

In studies of surfactant penetration into the eye, radiolabelled detergent was found to penetrate the rabbit cornea, to accumulate readily in ocular tissues and to be released slowly. Repeated applications led to increasing binding of the detergent. Permeability, ocular and systemic uptake and retention were all greater in juvenile than in adult rabbits. Preliminary tests of the effects of surfactants on ocular cells in vitro using concentrations found in vivo, suggest that some low-level effects might occur, particularly in juveniles.

Age Factors↗