Anne E. Warner

Gap junctional communication and compaction during preimplantation stages of mouse development

The ability of gap junction antibodies to block dye transfer and electrical coupling was examined in the compacted 8-cell mouse zygote. In control zygotes, Lucifer yellow injected into 1 cell transferred to the rest of the embryo. When antibodies raised against the major protein extracted from gap junctions were co-injected with Lucifer yellow, dye transfer failed in 86% of the zygotes tested and electrical coupling was almost completely inhibited. Subsequently, the antibody-containing cells were extruded. When the antibodies were injected into 1 cell at the 2-cell stage, 82% of the zygotes divided normally to the 8-cell stage. Cells containing gap junction antibodies were uncompacted, but continued to divide. We conclude that these antibodies inhibit gap junctional communication in the early mouse zygote and that communication through gap junctions may be involved in the maintenance of compaction.

Permeability of gap junctions at the segmental border in insect epidermis

We have examined cell-cell communication between epidermal cells of fifth-instar larvae of the milkweed bug Oncopeltus fasciatus and those of maggots of the blowfly Calliphora erythrocephala. Ionic coupling and the transfer of injected Lucifer Yellow (molecular weight 450) and lead-EDTA (molecular weight 374) were used to map the pattern of communication. All epidermal cells, regardless of their position with respect to the segmental border, were ionically coupled. In both species Lucifer yellow was transferred freely between cells lying in the same segment--that is, in the same developmental compartment as defined by cell lineage. Dye injections close to the segmental border showed that Lucifer Yellow was not transferred between cells in adjacent segments--that is, across the compartmental border. In Calliphora failure of Lucifer Yellow transfer at the segmental border was always observed; in Oncopeltus Lucifer Yellow was not transferred in 90% of preparations examined. Injections of PbEDTA2- in Calliphora showed that this anion was transferred freely from cell to cell and did not respect the segmental boundary. Previous studies of the distribution of gap junctions at and away from the segmental border make it unlikely that the failure of Lucifer Yellow to cross from segment to segment is due to reduced number of gap-junctional channels at the border. We conclude that gap junctions at the segmental borders may have different permeability properties from those between cells in the same segment.

The pH sensitivity of the chloride conductance of frog skeletal muscle

1. The effect of changes in the pH of the extracellular solution on the membrane conductance of frog sartorius and toe muscle fibres was measured with intracellular micro‐electrodes.

SPECIFIC MOTIFS IN THE EXTERNAL LOOPS OF CONNEXIN PROTEINS CAN DETERMINE GAP JUNCTION FORMATION BETWEEN CHICK HEART MYOCYTES

1. Gap junction formation was compared in the absence and presence of small peptides containing extracellular loop sequences of gap junction (connexin) proteins by measuring the time taken for pairs of spontaneously beating embryonic chick heart myoballs to synchronize beat rates. Test peptides were derived from connexin 32. Non‐homologous peptides were used as controls. Control pairs took 42 +/‐ 0.5 min (mean +/‐ S.E.M.; n = 1088) to synchronize. 2. Connexins 32 and 43, but not 26, were detected in gap junction plaques. The density and distribution of connexin immunolabelling varied between myoballs. 3. Peptides containing conserved motifs from extracellular loops 1 and 2 delayed gap junction formation. The steep portion of the dose‐response relation lay between 30 and 300 microM peptide. 4. In loop 1, the conserved motifs QPG and SHVR were identified as being involved in junction formation. In loop 2, the conserved SRPTEK motif was important. The ability of peptides containing the SRPTEK motif to interfere with the formation of gap junctions was enhanced by amino acids from the putative membrane‐spanning region. 5. Peptides from loop 1 and loop 2 were equivalently effective; there was no synergism between them. 6. The inclusion of conserved cysteines in test peptides did not make them more effective in the competition assay.

The electrical properties of the ectoderm in the amphibian embryo during induction and early development of the nervous system

1. The electrical properties of ectodermal cells have been studied in embryos of the axolotl Ambystoma mexicanum between gastrulation and the closure of the neural tube.

Computational challenges of systems biology

Progress in the study of biological systems such as the heart, brain, and liver will require computer scientists to work closely with life scientists and mathematicians. Computer science will play a key role in shaping the new discipline of systems biology and addressing the significant computational challenges it poses.

The distribution of sodium and potassium in amphibian embryos during early development

1. Intracellular and intercellular concentrations of sodium and potassium have been measured in pregastrular embryos of Xenopus laevis and Amblystoma mexicanum. Calcium and magnesium contents have also been determined.

Intracellular and intercellular potentials in the early amphibian embryo

1. The sensitivity of the membrane potential of cells of early embryos of Xenopus laevis to variations in the extracellular concentrations of sodium and potassium has been determined.

Kinetic properties of the chloride conductance of frog muscle

1. The anion conductance of frog muscle has been studied at alkaline, neutral and acid extracellular pH values using a voltage clamp technique. Potassium in the extracellular solution was replaced by rubidium in order to simplify the behavior of the cation conductance.

The voltage dependence of the chloride conductance of frog muscle

1. The effect of extracellular pH changes on the voltage—current relation of frog muscle membrane has been studied using intracellular microelectrodes. To reduce the cation conductance of the membrane, potassium in Ringer solution was replaced by rubidium.