Biomedical subjects

E M Munro

Publications and source records attributed to E M Munro.

3 recordsLinked to original sources

PubMed2000

The segment polarity network is a robust developmental module.

All insects possess homologous segments, but segment specification differs radically among insect orders. In Drosophila, maternal morphogens control the patterned activation of gap genes, which encode transcriptional regulators that shape the patterned expression of pair-rule genes. This patterning cascade takes place before cellularization. Pair-rule gene products subsequently 'imprint' segment polarity genes with reiterated patterns, thus defining the primordial segments. This mechanism must be greatly modified in insect groups in which many segments emerge only after cellularization. In beetles and parasitic wasps, for instance, pair-rule homologues are expressed in patterns consistent with roles during segmentation, but these patterns emerge within cellular fields. In contrast, although in locusts pair-rule homologues may not control segmentation, some segment polarity genes and their interactions are conserved. Perhaps segmentation is modular, with each module autonomously expressing a characteristic intrinsic behaviour in response to transient stimuli. If so, evolution could rearrange inputs to modules without changing their intrinsic behaviours. Here we suggest, using computer simulations, that the Drosophila segment polarity genes constitute such a module, and that this module is resistant to variations in the kinetic constants that govern its behaviour.

Animals↗

PubMed1999

Functional assessment of surface loops: deletion of eukaryote-specific peptide inserts in thymidylate synthase of Saccharomyces cerevisiae.

The primary structure is known for at least 29 thymidylate synthases and the crystal structure is known for several from both prokaryotes and eukaryotes. All these are markedly similar making thymidylate synthase one of the most highly conserved enzymes known. There are, however, two surface loops, one near the active site and the other near the dimer interface, which exist in distinctly prokaryotic and eukaryotic versions. Specifically, in eukaryotes these two surface loops have small peptide inserts conserved in size and partly conserved in sequence, that are not present in the prokaryotic thymidylate synthases. To address the possibility that these inserts provide eukaryote-specific functions the Saccharomyces cerevisiae loops were individually modified to mimic their prokaryotic counterparts. Altering the surface loop near the active site increased Km for the nucleotide substrate and decreased apparent Vmax. Mutant variants with alterations in the other surface loop were unable to dimerize. Therefore these surface loops have acquired, perhaps by way of the eukaryotic inserts, characteristics that are important for catalytic activity and quaternary structure respectively.

Alleles↗

PubMed1987

Scheduling and programming of rapid finger sequences: tests and elaborations of the hierarchical editor model.

Is a response sequence executed only after the sequence has been fully programmed, as discrete processing models predict, or does execution begin before programming has been completed, as continuous processing models predict? To address this issue, we tested a discrete processing model of human motor performance, the hierarchical editor model of Rosenbaum, Inhoff, and Gordon (1984). This model was developed to account for data from experiments in which people perform one of two possible finger sequences, depending on the identity of a choice signal. The model assumes a hierarchically organized motor program that is first "edited" to resolve any uncertainties and is then "executed" to produce the desired responses. Three experiments reported here show that, contrary to the model's predictions and some well-known motor programming results (Sternberg, Monsell, Knoll, & Wright, 1978), the reaction time to begin a response sequence actually decreases with the length of the sequence under some choice conditions. We account for these results with a model that allows execution to begin while editing is still in progress. A key assumption in the model is that subjects schedule execution so that means and variances of interresponse times are minimized.

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