Organization of the axolemma in amyelinated axons. A cytochemical study in dy/dy dystrophic mice.

Previous studies using a variety of techniques have shown that in normal myelinated fibres there are structural differences between the axon membrane at nodes of Ranvier and in the internodes beneath the myelin sheath. The present paper reports the results of a cytochemical study on the axon membrane in amyelinated axons in dy/dy dystrophic mice, in which myelination is focally absent owing to a genetic defect. The results indicate that the amyelinated axon membrane, which is known to be capable of sustaining continuous impulse conduction, is structurally different from normal nodal membrane. Comparison of the cytochemical results with physiological and pharmacological data suggests that the amyelinated dystrophic axon membrane may exhibit a lower sodium channel density than normal nodal membrane. Previous studies using a variety of techniques have shown that in normal myelinated fibres there are structural differences between the axon membrane at nodes of Ranvier and in the internodes beneath the myelin sheath. The present paper reports the results of a cytochemical study on the axon membrane in amyelinated axons in dy/dy dystrophic mice, in which myelination is focally absent owing to a genetic defect. The results indicate that the amyelinated axon membrane, which is known to be capable of sustaining continuous impulse conduction, is structurally different from normal nodal membrane. Comparison of the cytochemical results with physiological and pharmacological data suggests that the amyelinated dystrophic axon membrane may exhibit a lower sodium channel density than normal nodal membrane

Genetic control of programmed cell death in the Caenorhabditis elegans hermaphrodite germline.

Development of the nematode Caenorhabditis elegans is highly reproducible and the fate of every somatic cell has been reported. We describe here a previously uncharacterized cell fate in C. elegans: we show that germ cells, which in hermaphrodites can differentiate into sperm and oocytes, also undergo apoptotic cell death. In adult hermaphrodites, over 300 germ cells die, using the same apoptotic execution machinery (ced-3, ced-4 and ced-9) as the previously described 131 somatic cell deaths. However, this machinery is activated by a distinct pathway, as loss of egl-1 function, which inhibits somatic cell death, does not affect germ cell apoptosis. Germ cell death requires ras/MAPK pathway activation and is used to maintain germline homeostasis. We suggest that apoptosis eliminates excess germ cells that acted as nurse cells to provide cytoplasmic components to maturing oocytes

Three-dimensional structure of the bacteriophage P22 tail machine

The tail of the bacteriophage P22 is composed of multiple protein components and integrates various biological functions that are crucial to the assembly and infection of the phage. The three-dimensional structure of the P22 tail machine determined by electron cryo-microscopy and image reconstruction reveals how the five types of polypeptides present as 51 subunits are organized into this molecular machine through twelve-, six- and three-fold symmetry, and provides insights into molecular events during host cell attachment and phage DNA translocation

A convenient synthesis of difficult medium-sized cyclic peptides by Staudinger-mediated ring closure

Novel, efficient and mild preparation of 7- and 8-membered cyclic di- and 10-membered cyclic tripeptides containing alpha-, beta- or gamma-amino acid residues is effected by a Staudinger-mediated ring closure. Medium-sized cyclic di- and tripeptides - recognized as difficult targets - were obtained in moderate to good yields according to a straightforward sequence. Empirical force-field calculations were undertaken to determine their conformational behaviors and showed high levels of similarity with X-ray results. A computational study at the B3LYP/6-31+G** level of theory afforded information regarding the impact of the sequence, ring-size and substitution on the activation barriers for the cyclization of azido peptide thioesters