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H Keshishian

Publications and source records attributed to H Keshishian.

42 records · Page 3Linked to original sources
PubMed1983

Embryogenesis of peripheral nerve pathways in grasshopper legs. I. The initial nerve pathway to the CNS.

The founding of the first nerve path of the grasshopper metathoracic leg was examined at the level of identified neurons, using intracellular dye fills, immunohistochemistry, Nomarski optics, and scanning and transmission electron microscopy. The embryonic nerve is established by the axonal trajectory of a pair of afferent pioneer neurons, the tibial 1 (Ti1) cells. Following a period of profuse filopodial sprouting, the Ti1 axonal growth cones, possessing 75- to 100-microns-long filopodia, navigate a stereotyped path across the limb bud epithelium to the base of the appendage and into the CNS. The Ti1 axons grow from cell to cell along a chain of preaxonogenesis neurons spaced at intervals along the pathway, forming dye-passing junctions with them. The contacted neurons subsequently undergo axonogenesis and follow the pioneer axons into the CNS. Later arising neurons project their axons onto the cell bodies of the chain, thereby establishing the principal branch points of the nerve. Among the later arising afferents are the sensory neurons of the femoral chordotonal and subgenual organs. The morphology of the adult nerve appears to be determined by the stereotyped positioning of neurons in the differentiating limb bud and by the resultant axonal trajectories established during the first 10% of peripheral neurogenesis.

Animals↗
PubMed1983

Embryogenesis of peripheral nerve pathways in grasshopper legs. II. The major nerve routes.

In the preceding paper (H. Keshishian and D. Bentley, 1983a, Dev. Biol. 96, 89-102) the events leading to the morphogenesis of nerve 5B1 in the grasshopper embryonic metathoracic leg were presented. Here the role of later differentiating peripheral neurons in establishing the other major nerves of the leg is examined. In addition to the (tibial 1) (Ti1) pioneer neuron cell pairs that establish nerve 5B1 in the tibia femur, and coxa-trochanter, six later differentiating cells and/or cell pairs were identified and examined with respect to their role in peripheral nerve ontogeny. Nerve path pioneering was observed in two cell pairs of the distal tarsus (Ta1 and Ta2), by neurons of the posterior proximal tibia (Ti2), the posterior midfemur (neurons F3 and F4), and by an additional cell pair in the anterior coxal-trochanteral region of the limb bud (cell pair, CT2). In addition, efferent projections onto limb and epithelia played an important role in establishing nerve branches. In two nerves the axonal trajectory from the periphery to the CNS is established by afferent and efferent pathfinding axons meeting halfway and overgrowing each other's established projections. For each nerve branch examined it was found that axons projected initially to the cell bodies of previously arising neurons along the trajectory. The location along the limb bud ectoderm where neurons arise, and hence their ultimate cell body positions, played an important role in organizing the fasciculation of follower axons and establishing branch points.

Animals↗
PubMed1983

Embryogenesis of peripheral nerve pathways in grasshopper legs. III. Development without pioneer neurons.

We have examined the consequence of deleting the first pathfinding neurons to differentiate in the metathoracic leg, cell pair tibial 1 (Ti1) (C. M. Bate, 1976, Nature (London) 260, 54-56; H. Keshishian, 1980, Dev. Biol. 80, 388-397) on the development of two uniquely identifiable follower sensory neurons, and upon the subsequent development of nerve 5B1 in the leg. Following the equivalent of 10-15% of embryonic development in culture the follower sensory neurons were found to have formed topologically normal axonal trajectories in the leg, and to have established contacts with later differentiating sensory and motor axons in an essentially normal fashion. The results show that followers can navigate the route normally taken by the pioneers, and suggest that the pioneers do not have unusual pathfinding capabilities.

Animals↗
PubMed1979

Quantitative staging of embryonic development of the grasshopper, Schistocerca nitens.

During development of the grasshopper embryo, it is feasible to examine the structure, pharmacology, and physiology of uniquely identified cells. These experiments require a fast, accurate staging system suitable for live embryos. We present a system comprising (1) subdivision of embryogenesis into equal periods, (2) expression of stage in percent of complete embryogenesis time, (3) characterization of stages by light micrographs (and descriptive test), and (4) illustration of stages at the egg, embryo, and limb levels of resolution. Advantages of a percent-system include communicability, flexibility in temporal resolution, accurate assignment of elapsed time in developmental processes, and uniform coverage of the period of embryogenesis. The stages described are at 5% intervals with an estimated error of +/- 1%.

Animals↗
PubMedDate not supplied

Peptides as affinity surfaces for protein purification.

The tetrapeptide GPRP was previously shown to be an effective affinity ligand for fibrinogen when immobilized to Fractogel (Kuyas et al., 1990). The authors synthesized the GPRP peptide directly onto an aminefunctionalized POROS chromatographic resin to demonstrate the effectiveness of this approach for generating perfusive affinity media. Fibrinogen from plasma bound to an NH2-GPRP-POROS column under 50 mM phosphate buffer, 0.15 M NaCl, pH 7 at 15 ml/min flow rate. The bound fibrinogen showed weak clotting activity when eluted with 20 mM acetate buffer, pH 4. The peptide column did not bind denatured fibrinogen. The dynamic binding capacity of the column by frontal analysis was 10.2 mg/ml column volume. The total analysis time was under 5 min. Similarly, the CAQCHTVEK peptide of cytochrome c with heme group covalently attached to the SH groups of the two cysteines is known to bind to albumins (Adams et al., 1989). A simplified peptide analogue, GAQGHTVEK, was synthesized directlyon POROS resin. Under 20 mM MES, pH 6, albumin from human serum bound specifically to this peptide column and eluted with a salt gradient at 0.2 M NaCl, 20 mM MES (2-[N-Morpholino]ethane sulfonic acid), pH 6. The dynamic binding capacity of human serum albumin by frontal analysis was 19 mg/ml column volume. Thus, this column can purify albumin from human serum under non-denaturing conditions.

Chromatography, Affinity↗