Circular, double-stranded DNA molecules were injected into nuclei of mouse oocytes and one-or two-cell embryos to determine whether specific sequences were required to replicate DNA during mouse development.Although all of the injected DNAs were stable, replication of plasmid pML-l DNA was not detected unless it contained either polyomavirus (PyV) or simian virus 40 (SV40) DNA sequences. Replication occurred in embryos, but not in oocytes. PyV DNA, either alone or recombined with pML-l, underwent multiple rounds of replication to produce superhelical and relaxed circular monomers after injection into one-or two-cell embryos. SV40 DNA also replicated, but only 3% as well as PyV DNA. Coinjection of PyV DNA with either pML-1 or SV40 had no effect on the replicating properties of the three DNAs. These results are consistent with a requirement for specific cis-acting sequences to replicate DNA in mammalian embryos, in contrast to sequence-independent replication of DNA injected into Xenopus eggs. Furthermore, PyV DNA replication in mouse embryos required PyV large T-antigen and either the a-,8-core or ,-core configuration of the PyV origin of replication. Although the a-core configuration replicated in differentiated mouse cells, it failed to replicate in mouse embryos, demonstrating cell-specific activation of an origin of replication. Replication or expression of PyV DNA interfered with normal embryonic development. These results reveal that mouse embryos are permissive for PyV DNA replication, in contrast to the absence of PyV DNA replication and gene expression in mouse embryonal carcinoma cells.Although ori sequences have not yet been demonstrated as functional elements of eucaryotic chromosomes, they are implicated strongly by the temporal order of gene replication (11, 36); the selective amplification of specific genes (53,65,74); the existence of autonomously replicating sequences (26,76); and the fact that all bacterial, viral, plasmid, and organelle genomes require one or more unique cis-acting sequences that act as origins of replication (ori) and interact with specific gene products. However, some observations suggest that DNA replication during the early stages of embryonic development may not require sequence-specific origins of replication to carry out DNA replication.Analysis of DNA replication in Drosophila melanogaster (6,56,85) has revealed that the average distance between chromosome replication bubbles in preblastomere embryos is at least five times smaller than that in differentiated cells, suggesting that embryos initiate replication at many more sequences than do differentiated cells of the same species. Furthermore, injection of DNA into Xenopus eggs revealed that semiconservative DNA replication can occur under the apparent control of the cell division cycle but with no apparent requirement for specific DNA sequences (34,57,58). All of the DNA molecules examined, including simian virus 40 (SV40) and polyomavirus (PyV) DNA which normally replicate only in differentiated cells of a specific m...
A major pre-P-amyloid proteinsps (APP,,,) processing activity from Alzheimer's disease brain extracts was identified and found to be indistinguishable from the activity of cathepsin D.APP,, processing activity cleaved APP,,, into a series of fragments that reacted on immunoblots to a monoclonal antibody (C286.8a) against p-amyloid-( 1 -7)-peptide and cleaved N-dansyl-APP-(591-601)-amide at the Glu-Val and Met-Asp bonds. Fragments of 5.5 kDa and 10-12 kDa were formed from the cleavage of APP,,, by cathepsin D at the Glu593-Val594 bond, and had the same Nterminus as a minor form of P-amyloid released by cells. Abbreviations. APP,,,, pre-P-amyloid protein,,, isoform; [N5", L5'6]APP,,,, APP,,, with lysine and methionine at positions 595 and 596 replaced by asparagine and leucine, respectively; dansyl, 5-(dimethylamino)-napthalene-1-sulfonyl; N-dansyl-APP-(591-601)-amide, N-dansyl-ISEVKMDAEFR-amide; C286.8a, IgG,, mAb recognizing P-amyloid residues at positions 1-7; PhMeSO,F, phenylmethylsulfonyl fluoride; E-64, trans-epoxysuccinyl-L-leucylamido(4-guanidino)butane; P-2, post-I5000 g pellet.Enzymes. Cathepsin D (EC 3.4.23.5); type I1 site-specific deoxyribonucleases (EC 3.1.21.4).-~ processing enzyme, the activity of which is influenced by a mutation associated with the Swedish pedigree of familial Alzheimer's disease. MATERIALS AND METHODSHuman cathepsin D from Calbiochem was pure by SDS/ PAGE, 93% accurate by amino acid analysis, and contained only cathepsin D derived N-termini, the majority of which were from equimolar amounts of the mature light (GPI-PEVLKNY-), and heavy (GGVKVERQVF-) chains. Pepstatin A and heparin agarose were from Sigma. Mono-Q columns were from Pharmacia. Rabbit antiserum to human cathepsin D was from Dako Corp. IgG was purified from rabbit sera using Avid AL [23] and coupled to CnBr-activated Sepharose 4B [24]. The methods and instrumentation for peptide synthesis [25], amino acid analysis [26] and mass spectrocopy [26] were as cited previously. The protein content of crude extracts was determined by the Bradford assay [27].
Axonal growth and neurological recovery after traumatic spinal cord injury (SCI) is limited by the presence of inhibitory proteins in myelin, several of which act via the NgR1 protein in neurons. A truncated soluble ligand-binding fragment of NgR1 serves as a decoy and promotes recovery in acute and chronic rodent SCI models. To develop the translational potential of these observations, we created a human sequence-derived NgR1(310)-Fc protein. This protein is active in vitro. When the human NgR1 decoy is administered by continuous intracerebroventricular infusion to rats with a spinal contusion injury at doses of 0.09-0.53 mg/kg/d, neurological recovery is improved. Effective doses double the percentage of rats able to bear weight on their hindlimbs. Next, we considered the half-life and distribution of NgR1(310)-Fc after bolus delivery to the lumbar intrathecal space. The protein is found throughout the neuraxis and has a tissue half-life of approximately 2 days in the rat, and 5 days in the nonhuman primate. At an intermittent, once every 4 day, lumbar bolus dosing schedule of 0.14 mg/kg/d, NgR1(310)-Fc promoted locomotor rat recovery from spinal cord contusion at least as effectively as continuous infusion in open field and grid walking tasks. Moreover, the intermittent lumbar NgR1(310)-Fc treatment increased the growth of raphespinal axons into the lumbar spinal cord after injury. Thus, human NgR1(310)-Fc provides effective treatment for recovery from traumatic SCI in this preclinical model with a simplified administration regimen that facilitates clinical testing.
To determine the requirements for gene expression in mammalian germ cells, circular double-stranded simian virus 40 (SV40) DNA molecules containing deletions in sequences controlling transcription and replication were injected into the nucleus of mouse oocytes. Expression of large (T-Ag) and small (t-Ag) tumor antigens ("early gene products") required at least three GGGCGG boxes, but did not require either the origin of viral DNA replication (or/) or a TATA box. Expression of capsid antigen VP1 ("late gene products") required at least three GGGCGG boxes, sequences between nucleotides 197 and 273 in the 72-bp repeat region, and transactivation by T-Ag. These results are consistent with the requirements for expression of the same genes in differentiated mammalian cells. Surprisingly, however, the 72-bp repeats ("enhancer elements") that are required for expression of T-Ag and t-Ag genes in differentiated cells were not required in mouse oocytes. Similarly, expression of both the early and late genes was unaffected in mouse oocytes by the absence of either DNA replication or an intact ori sequence, components required for maximum expression of late genes in differentiated cells. Thus, mammalian oocytes effectively utilize promoters that are fully active in mammalian differentiated cells only when associated with either enhancer elements or DNA replication. Furthermore, requirements for expression of SV40 genes in mouse oocytes are distinctly different from those reported for Xenopus oocytes. This suggests that caution should be exercised when extrapolating conclusions drawn from experiments with amphibian germ cells to mammalian germ cells.
Alzheimer's disease is characterized by widespread deposition of amyloid in the central nervous system. The 4-kilodalton amyloid beta protein is derived from a larger amyloid precursor protein and forms amyloid deposits in the brain by an unknown pathological mechanism. Except for aged nonhuman primates, there is no animal model for Alzheimer's disease. Transgenic mice expressing amyloid beta protein in the brain could provide such a model. To investigate this possibility, the 4-kilodalton human amyloid beta protein was expressed under the control of the promoter of the human amyloid precursor protein in two lines of transgenic mice. Amyloid beta protein accumulated in the dendrites of some but not all hippocampal neurons in 1-year-old transgenic mice. Aggregates of the amyloid beta protein formed amyloid-like fibrils that are similar in appearance to those in the brains of patients with Alzheimer's disease.
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