Reorganization of Synaptic Connections and Perineuronal Nets in the Deep Cerebellar Nuclei of Purkinje Cell Degeneration Mutant Mice.

The perineuronal net (PN) is a subtype of extracellular matrix appearing as a net-like structure around distinct neurons throughout the whole CNS. PNs surround the soma, proximal dendrites, and the axonal initial segment embedding synaptic terminals on the neuronal surface. Different functions of the PNs are suggested which include support of synaptic stabilization, inhibition of axonal sprouting, and control of neuronal plasticity. A number of studies provide evidence that removing PNs or PN-components results in renewed neurite growth and synaptogenesis. In a mouse model for Purkinje cell degeneration, we examined the effect of deafferentation on synaptic remodeling and modulation of PNs in the deep cerebellar nuclei. We found reduced GABAergic, enhanced glutamatergic innervations at PN-associated neurons, and altered expression of the PN-components brevican and hapln4. These data refer to a direct interaction between ECM and synapses. The altered brevican expression induced by activated astrocytes could be required for an adequate regeneration by promoting neurite growth and synaptogenesis.

Slow switchover from host RNA synthesis to bacteriophage RNA synthesis after infection of Escherichia coli with a T4 mutant defective in the bacteriophage T4-induced unfolding of the host nucleoid.

Most, if not all, host RNA synthesis was shut off after infection of Escherichia coli strain B/5 with a bacteriophage T4 multiple mutant defective in the abilities to induce (i) unfolding of the host nucleoid (unf-), (ii) nuclear disruption (ndd-), and (iii) host DNA degradation (denA-, denB-). The shutoff of host RNA synthesis and turn-on of phage RNA synthesis were slower after infection of E. coli with unf- phage than after infection with unf+ phage. This delay in the switchover from host RNA synthesis to phage RNA synthesis in unf- infections did not result in a measurable delay in the onset of nuclear disruption, deoxyribonucleoside monophosphate kinase synthesis, or DNA synthesis. unf39 did not complement alc (allows late transcription on cytosine-containing DNA) mutants, supporting the proposal of Sirotkin et al. [Nature (London) 265:28-32, 1977] that alc and unf are possibly the same gene.

Shutoff of host RNA synthesis in bacteriophage T4-infected Escherichia coli in the absence of host DNA degradation and nuclear disruption.

In contrast to its effect on host DNA synthesis, nuclear disruption in phage T4-infected Escherichia coli B/5 cells has no effect on the shutoff of host RNA synthesis. Host RNA synthesis is shut off normally after infection with T4 multiple mutants that fail to induce both nuclear disruption and host DNA degradation.

Mutants of bacteriophage T4 deficient in the ability to induce nuclear disruption: shutoff of host DNA and protein synthesis gene dosage experiments, identification of a restrictive host, and possible biological significance.

The shutoff of host DNA synthesis is delayed until about 8 to 10 min after infection when Escherichia coli B/5 cells were infected with bacteriophage T4 mutants deficient in the ability to induce nuclear disruption (ndd mutants). The host DNA synthesized after infection with ndd mutants is stable in the absence of T4 endonucleases II and IV, but is unstable in the presence of these nucleases. Host protein synthesis, as indicated by the inducibility of beta-galactosidase and sodium dodecyl sulfate-polyacrylamide gel patterns of isoptopically labeled proteins synthesize after infection, is shut off normally in ndd-infected cells, even in the absence of host DNA degradation. The Cal Tech wild-type strain of E. coli CT447 was found to restrict growth of the ndd mutants. Since T4D+ also has a very low efficiency of plating on CT447, we have isolated a nitrosoguanidine-induced derivative of CT447 which yields a high T4D+ efficiency of plating while still restricting the ndd mutants. Using this derivative, CT447 T4 plq+ (for T4 plaque+), we have shown that hos DNA degradation and shutoff of host DNA synthesis occur after infection with either ndd98 X 5 (shutoff delayed) or T4D+ (shutoff normal) with approximately the same kinetics as in E. coli strain B/5. Nuclear disruption occurs after infection of CT447 with ndd+ phage, but not after infection with ndd- phage. The rate of DNA synthesis after infection of CT447 T4 plq+ with ndd98 X 5 is about 75% of the rate observed after infection with T4D+ while the burst size of ndd98 X 5 is only 3.5% of that of T4D+. The results of gene dosage experiments using the ndd restrictive host C5447 suggest that the ndd gene product is required in stoichiometric amounts. The observation by thin-section electron microscopy of two distinct pools of DNA, one apparently phage DNA and the other host DNA, in cells infected with nuclear disruption may be a compartmentalization mechanism which separates the pathways of host DNA degradation and phage DNA biosynthesis.

Identification and preliminary characterization of a mutant defective in the bacteriophage T4-induced unfolding of the Escherichia coli nucleoid.

The nucleoids of Escherichia coli S/6/5 cells are rapidly unfolded at about 3 min after infection with wild-type T4 bacteriophage or with nuclear disruption deficient, host DNA degradation-deficient multiple mutants of phage T4. Unfolding does not occur after infection with T4 phage ghosts. Experiments using chloramphenicol to inhibit protein synthesis indicate that the T4-induced unfolding of the E. coli chromosomes is dependent on the presence of one or more protein synthesized between 2 and 3 min after infection. A mutant of phage T4 has been isolated which fails to induce this early unfolding of the host nucleoids. This mutant has been termed "unfoldase deficient" (unf-) despite the fact that the function of the gene product defective in this strain is not yet known. Mapping experiments indicate that the unf- mutation is located near gene 63 between genes 31 and 63. The folded genomes of E. coli S/6/5 cells remain essentially intact (2,000-3,000S) at 5 min after infection with unfoldase-, nuclear disruption-, and host DNA degradation-deficient T4 phage. Nuclear disruption occurs normally after infection with unfoldase- and host DNA degradation-deficient but nuclear disruption-proficient (ndd+), T4 phage. The host chromosomes remain partially folded (1,200-1,800S) at 5 min after infection with the unfoldase single mutant unf39 x 5 or an unfoldase- and host DNA degradation-deficient, but nuclear disruption-proficient, T4 strain. The presence of the unfoldase mutation causes a slight delay in host DNA degradation in the presence of nuclear disruption but has no effect on the rate of host DNA degradation in the absence of nuclear disruption. Its presence in nuclear disruption- and host DNA degradation-deficient multiple mutants does not alter the shutoff to host DNA or protein synthesis.