A role for decorin in controlling proliferation, adhesion, and migration of murine embryonic fibroblasts.

The proteoglycan decorin putatively inhibits cell adhesion and cell migration on various extracellular matrix substrates through interactions with beta(1) integrins. This study, therefore, examined the adhesive, migration, and proliferative characteristics of decorin knockout (Dcn(-/-)) murine embryonic fibroblasts compared to wild-type controls on collagen-coated, fibronectin-coated, and uncoated tissue culture plates. The Dcn(-/-) cells showed significantly greater proliferation than wild-type controls on all substrates. The Dcn(-/-) cells also showed significantly greater adhesion to both collagen and fibronectin; both cell types showed greater adhesion to collagen. The addition of exogenous decorin had a differential effect on adhesion to collagen between cell types, but not on fibronectin. For collagen, blocking either alpha(2) or beta(1) integrin subunits significantly reduced adhesion for Dcn(-/-) cells; whereas for fibronectin, blocking either the alpha(5) or beta(1) integrin subunits reduced adhesion for both cell types. Decorin and the alpha(5)beta(1) integrin may have lesser roles in adhesion to fibronectin than previously presumed. Finally, compared to wild-type cells, Dcn(-/-) cells showed greater migration on both uncoated and collagen substrates. This study demonstrates that decorin affects the biology of various integrins that participate in cell proliferation, adhesion, and migration on various substrates.

Induction of manganese superoxide dismutase in acute spinal cord injury.

Free radical-mediated mechanisms of cellular damage have been implicated in the early stages of spinal cord injury (SCI). Manganese superoxide dismutase (MnSOD) is a potent scavenger of superoxide radicals and likely serves an important cytoprotective role in preventing cellular damage after SCI. We have evaluated the expression of MnSOD to address its role during the early events of SCI using a well-established rat contusion model. Northern analysis showed a rapid induction of MnSOD mRNA between 2 and 6 h post injury. Observed time-dependent increases in MnSOD message was maximal 6 h post injury over that of MnSOD mRNA levels induced by laminectomy alone. Immunoblot and immunohistochemical analysis demonstrated increased expression of MnSOD protein 24 h after SCI with localization primarily within neurons. Interestingly, laminectomy alone also caused an induction of MnSOD gene and protein expression. To evaluate one potential mechanism of MnSOD induction, we microinjected the naive spinal cord with IL-1beta, which caused a similar fold induction of MnSOD mRNA levels by 6 h as observed with SCI, thus implicating it as a potential inducer of MnSOD during SCI. In summary, these results demonstrate that this potent cytoprotective antioxidant enzyme is rapidly and significantly induced as a consequence of SCI.

Systemic administration of a calpain inhibitor reduces behavioral deficits and blood-brain barrier permeability changes after experimental subarachnoid hemorrhage in the rat.

Increases in intracellular calcium and subsequent activation of calcium-activated proteases (e.g., calpains) may play a critical role in central nervous system injury. Several studies have implicated calpain activation following subarachnoid hemorrhage (SAH). This study evaluated the effect of a calpain inhibitor administration following SAH in the rat on behavioral deficits (postinjury days 1-5, employing a battery of well-characterized assessment tasks), and blood-brain barrier permeability changes (48 h post-SAH, quantifying the microvascular alterations according to the extravasation of protein-bound Evans Blue using a spectrophotofluorimetric technique). Rats were injected with 400 microl of autologous blood into the cisterna magna to induce SAH. Within 5 min after the surgical procedure, Calpain Inhibitor II or vehicle was continuously administered intravenously for 2 days. Results indicated that Calpain Inhibitor II treatment after SAH significantly improved (a) beam balance time (day 1, p < 0.05), but not beam balance score, (b) latency to traverse the beam on days 1-4 (day 1-3, p < 0.001; day 4, p < 0.01), and (c) loss in body weight on days 4-5 (p < 0.05). Evans Blue dye extravasation was significantly less in SAH Calpain Inhibitor II-treated rats compared to SAH vehicle-treated rats in seven out of the eight brain regions studied (p < 0.001, 0.01, and 0.05). These results suggest that pharmacological inhibition of a relatively selective, membrane-permeant calpain inhibitor can significantly reduce some pathophysiological SAH consequences, and indicate that the inhibition of calpain may be a beneficial therapeutic approach to reduce post-SAH global brain dysfunction.

Feasibility and safety of neural tissue transplantation in patients with syringomyelia.

Transplantation of fetal spinal cord (FSC) tissue has demonstrated significant potential in animal models for achieving partial anatomical and functional restoration following spinal cord injury (SCI). To determine whether this strategy can eventually be translated to humans with SCI, a pilot safety and feasibility study was initiated in patients with progressive posttraumatic syringomyelia (PPTS). A total of eight patients with PPTS have been enrolled to date, and this report presents findings for the first two patients through 18 months postoperative. The study design included detailed assessments of each subject at multiple pre- and postoperative time points. Outcome data were then compared with each subject's own baseline. The surgical protocol included detethering, cyst drainage, and implantation of 6-9-week postconception human FSC tissue. Immunosuppression with cyclosporine was initiated a few days prior to surgery and continued for 6 months postoperatively. Key outcome measures included: serial magnetic resonance imaging (MRI) exams, standardized measures of neurological impairment and functional disability, detailed pain assessment, and extensive neurophysiological testing. Through 18 months, the first two patients have been stable neurologically and the MRIs have shown evidence of solid tissue at the graft sites, without evidence of donor tissue overgrowth. Although it is still too soon to draw any firm conclusions, the findings from the initial two patients in this study suggest that intraspinal grafting of human FSC tissue is both feasible and safe.

Neurophysiological assessment of the feasibility and safety of neural tissue transplantation in patients with syringomyelia.

The feasibility and safety of a procedure involving fetal spinal cord tissue transplantation in patients with syringomyelia was assessed using a neurophysiological protocol designed to quantitate peripheral nerve function, spinal cord reflex excitability, and spinal cord conduction pathways essential for somatosensory evoked potentials. We report here data obtained before and for 18 months following the transplantation procedure performed on the first two patients in this study. The neurophysiological assessment protocols included measures of cortical and spinal cord evoked potentials, H-reflex excitability, and peripheral nerve conduction. Prior to the procedure, both patients had significant deficits on some of the neurophysiological measures, for example, lower extremity cortical evoked potentials. However, robust measures of intact pathways, such as upper extremity cortical evoked potentials, were also observed preoperatively in both patients. Thus, it was anticipated that conduction in these intact pathways could be at risk either from complications from the transplantation procedure and/or from continued expansion of the syrinx. Following the transplantation procedure, no negative changes were observed in any of the neurophysiological measures in either patient. In addition, patient 1 showed a decrease in the rate potentiation of tibial H-reflexes on the right side and an increase in the response probability of left tibial H-reflexes. The results of this postoperative longitudinal assessment provide a first-level demonstration of the safety of the intraspinal neural tissue transplantation procedure. However, the consideration of safety is currently limited to the grafting procedure itself, since the long-term fates of the donor tissue in these two patients remain to be shown more definitively.

Influenza B and C virus NEP (NS2) proteins possess nuclear export activities.

Nucleocytoplasmic transport of viral ribonucleoproteins (vRNPs) is an essential aspect of the replication cycle for influenza A, B, and C viruses. These viruses replicate and transcribe their genomes in the nuclei of infected cells. During the late stages of infection, vRNPs must be exported from the nucleus to the cytoplasm prior to transport to viral assembly sites on the cellular plasma membrane. Previously, we demonstrated that the influenza A virus nuclear export protein (NEP, formerly referred to as the NS2 protein) mediates the export of vRNPs. In this report, we suggest that for influenza B and C viruses the nuclear export function is also performed by the orthologous NEP proteins (formerly referred to as the NS2 protein). The influenza virus B and C NEP proteins interact in the yeast two-hybrid assay with a subset of nucleoporins and with the Crm1 nuclear export factor and can functionally replace the effector domain from the human immunodeficiency virus type 1 Rev protein. We established a plasmid transfection system for the generation of virus-like particles (VLPs) in which a functional viral RNA-like chloramphenicol acetyltransferase (CAT) gene is delivered to a new cell. VLPs generated in the absence of the influenza B virus NEP protein were unable to transfer the viral RNA-like CAT gene to a new cell. From these data, we suggest that the nuclear export of the influenza B and C vRNPs are mediated through interaction between NEP proteins and the cellular nucleocytoplasmic export machinery.

Intact aggrecan and fragments generated by both aggrecanse and metalloproteinase-like activities are present in the developing and adult rat spinal cord and their relative abundance is altered by injury.

Aggrecan is a large proteoglycan (PG) that has been grouped with different PG families on the basis of its physical characteristics. These families include the chondroitin sulfate PGs, which appear to inhibit the migration of cells and axons during development. Although aggrecan has been studied primarily in cartilage, in the present study, tissue samples from developing, mature, and injured-adult rat spinal cords were used to determine whether aggrecan is present in the mammalian spinal cord. By the use of Western blot analysis, tissues were probed with aggrecan-specific antibodies (ATEGQV, TYKHRL, and LEC-7) and aggrecan-specific neoepitope antibodies (NITEGE, FVDIPEN, and TFKEEE) to identify full-length aggrecan and several fragments. Unlike many other aggrecan gene family members, aggrecan species were similar in embryonic day 14, postnatal day 1, and adult spinal cords. Spinal cord injury caused significant decreases in aggrecan. Partial recovery in some aggrecan species was evident by 2 weeks after injury. The presence of specific aggrecan neoepitopes suggested that aggrecan is cleaved in the spinal cord by both a disintegrin and metalloproteinase thrombospondin (also known as aggrecanase) and metalloproteinase-like activities. Many aggrecan species found in the spinal cord were similar to species in cartilage. Additional antibodies were used to identify two other aggrecan gene family members, neurocan and brevican, in the adult spinal cord. These studies present novel information on the aggrecan core protein species and enzymes involved in aggrecan cleavage in vivo in the rat spinal cord throughout development and after injury. They also provide the basis for investigating the function of aggrecan in the spinal cord.

TNF-alpha stimulates caspase-3 activation and apoptotic cell death in primary septo-hippocampal cultures.

Primary septo-hippocampal cell cultures were incubated in varying concentrations of tumor necrosis factor (TNF-alpha; 0.3-500 ng/ml) to examine proteolysis of the cytoskeletal protein alpha-spectrin (240 kDa) to a signature 145 kDa fragment by calpain and to the apoptotic-linked 120-kDa fragment by caspase-3. The effects of TNF-alpha incubation on morphology and cell viability were assayed by fluorescein diacetate-propidium iodide (FDA-PI) staining, assays of lactate dehydrogenase (LDH) release, nuclear chromatin alterations (Hoechst 33258), and internucleosomal DNA fragmentation. Incubation with varying concentrations of TNF-alpha produced rapid increases in LDH release and nuclear PI uptake that were sustained over 48 hr. Incubation with 30 ng/ml TNF-alpha yielded maximal, 3-fold, increase in LDH release and was associated with caspase-specific 120-kDa fragment but not calpain-specific 145-kDa fragment as early as 3.5 hr after injury. Incubation with the pan-caspase inhibitor, carbobenzosy- Asp-CH(2)-OC (O)-2-6-dichlorobenzene (Z-D-DCB, 50-140 microM) significantly reduced LDH release produced by TNF-alpha. Apoptotic-associated oligonucleosomal-sized DNA fragmentation on agarose gels was detected from 6 to 72 hr after exposure to TNF-alpha. Histochemical changes included chromatin condensation, nuclear fragmentation, and formation of apoptotic bodies. Results of this study suggest TNF-alpha may induce caspase-3 activation but not calpain activation in septo-hippocampal cultures and that this activation of caspase-3 at least partially contributes to TNF-alpha-induced apoptosis.

Stretch injury causes calpain and caspase-3 activation and necrotic and apoptotic cell death in septo-hippocampal cell cultures.

Traumatic brain injury (TBI) results in numerous central and systemic responses that complicate interpretation of the effects of the primary mechanical trauma. For this reason, several in vitro models of mechanical cell injury have recently been developed that allow more precise control over intra- and extracellular environments than is possible in vivo. Although we recently reported that calpain and caspase-3 proteases are activated after TBI in rats, the role of calpain and/or caspase-3 has not been examined in any in vitro model of mechanical cell injury. In this investigation, varying magnitudes of rapid mechanical cell stretch were used to examine processing of the cytoskeletal protein alpha-spectrin (280 kDa) to a signature 145-kDa fragment by calpain and to the apoptotic-linked 120-kDa fragment by caspase-3 in septo-hippocampal cell cultures. Additionally, effects of stretch injury on cell viability and morphology were assayed. One hour after injury, maximal release of cytosolic lactate dehydrogenase and nuclear propidium iodide uptake were associated with peak accumulations of the calpain-specific 145-kDa fragment to alpha-spectrin at each injury level. The acute period of calpain activation (1-6 h) was associated with subpopulations of nuclear morphological alterations that appeared necrotic (hyperchromatism) or apoptotic (condensed, shrunken nuclei). In contrast, caspase-3 processing of alpha-spectrin to the apoptotic-linked 120-kDa fragment was only detected 24 h after moderate, but not mild or severe injury. The period of caspase-3 activation was predominantly associated with nuclear shrinkage, fragmentation, and apoptotic body formation characteristic of apoptosis. Results of this study indicate that rapid mechanical stretch injury to septo-hippocampal cell cultures replicates several important biochemical and morphological alterations commonly observed in vivo brain injury, although important differences were also noted.

Chondroitin sulfate proteoglycan immunoreactivity increases following spinal cord injury and transplantation.

Extrinsic factors appear to contribute to the lack of regeneration in the injured adult spinal cord. It is likely that these extrinsic factors include a group of putative growth inhibitory molecules known as chondroitin sulfate proteoglycans (CSPGs). The aims of this study were to determine: (1) the consequences of spinal cord contusion injury on CSPG expression, (2) if CSPGs can be degraded in vivo by exogenous enzyme application, and (3) the effects of intraspinal transplantation on the expression of CSPGs. Chondroitin 6-sulfate proteoglycan immunoreactivity (CSPG-IR) dramatically increased following spinal cord contusion injury both at and adjacent to the injury site compared to normal controls (no surgical procedure) and laminectomy-only controls by 4 days postinjury. The dramatic increase in CSPG-IR persisted around the lesion and in the dorsal one-half to two-thirds of the spinal cord for at least 40 days postinjury. Glial fibrillary acidic protein (GFAP)-IR patterns were similarly intensified and spatially restricted as CSPG-IR patterns. These results suggest that: (1) CSPGs may contribute to the lack of regeneration following spinal cord injury and (2) astrocytes may contribute to the production of CSPGs. In addition, our results show that CSPGs could be cleaved in vivo with exogenous chondroitinase ABC application. This demonstration of cleavage may the basis for a model to directly assess CSPGs' role in growth inhibition in vivo (studies in progress) and hold potential as a therapeutic approach to enhance growth. Interestingly, the robust, injury-induced CSPG-IR patterns were not altered by intraspinal grafts of fetal spinal cord. The CSPG expression profile in the host spinal cord was similar to time-matched contusion-only animals. This was also true of GFAP-IR patterns. Furthermore, the fetal spinal cord tissue, which was generally CSPG negative at the time of transplantation, developed robust CSPG expression by 30 days posttransplantation. This increase in CSPG expression in the graft was paired with a moderate increase in GFAP-IR. CSPG-IR patterns suggest that these molecules may contribute to the limited regeneration seen following intraspinal transplantation. In addition, it suggests that the growth permissiveness of the graft may change overtime as CSPG expression develops within the graft. These correlations in the injured and transplanted spinal cord support CSPGs' putative growth inhibitory effect in the adult spinal cord.

Developmental patterns of BCL-2 and BCL-X polypeptide expression in the human spinal cord.

The cell death suppressors bcl-2 and bcl-x are developmentally regulated and may modulate physiologic cell death in the central nervous system (CNS). However, little data are currently available on the expression patterns of these polypeptides in the human CNS. We examined the ontogeny of bcl-2 and bcl-x in 12 human spinal cords of gestational ages (GA) between 5 and 39 weeks and in 3 adult cords. Paraffin sections were probed by immunohistochemistry using well-characterized, commercially available antibodies that had been raised against poorly conserved epitopes of these homologous proteins. Between 5 and 10 weeks GA, bcl-2 immunoreactivity was identified in primitive neuroepithelial cells of the ventricular zone. Individual cells of the mantle zone were stained including clusters of early anterior horn cells. Bcl-x immunoreactivity was most prominent in differentiating neurons of the mantle zone and less pronounced in the ventricular zone. Between 10 and 14 weeks GA, bcl-2 staining was observed in cells lining the central canal, neurons of the dorsal horn (especially laminae I and II), and in anterior horn cells. The latter exhibited a range of staining intensities from moderate to nondetectable. Bcl-2 immunoreactivity became markedly reduced between 15 and 25 weeks GA, persisting only in ependymal cells. In contrast, strong bcl-x staining was observed in most neurons throughout development and into adulthood. The period of apparent bcl-2 down-regulation overlaps with a peak in physiologic motoneuron death and the establishment of functional neuromuscular synapses in the human spinal cord. These findings suggest that bcl-2 and bcl-x may both be required for survival of early postmitotic neurons before appropriate synaptic connections have been established. Continued neuronal survival (after bcl-2 is down-regulated) may require persistent bcl-x expression in addition to target-derived neurotrophic factors made available through the formation of appropriate synapses.

Erythropoietin and erythropoietin receptor in the developing human central nervous system.

We have previously shown the presence of erythropoietin (Epo) within the spinal fluid of normal preterm and term infants, and the presence of Epo receptor (Epo-R) in the spinal cords of human fetuses. It is not known, however: 1) whether cells within the fetal central nervous system (CNS) express Epo; 2) if so, whether this expression changes with development; 3) which cells within the CNS express Epo-R; 4) whether Epo-R expression within the CNS changes with development; and 5) whether Epo-R within the fetal CNS are functional. Expression of mRNA for Epo and Epo-R was sought by reverse transcription-PCR in mixed primary cultures of fetal spinal cords as well as NT2 and hNT cells, human cell lines of neuronal precursors and mature neurons, respectively. Epo was measured by ELISA in spent media from primary cell culture, and immunohistochemistry was used to identify Epo-R on neurons and glia in cell culture, and in brain sections. Developmental changes in Epo and Epo-R expression were sought in spinal cords and brains from fetuses of 7-24 wk postconception by semiquantitative PCR. To assess Epo-R function, NT2 cells were exposed to conditions which stimulate programmed cell death, and rescue from apoptosis by the addition of recombinant Epo was evaluated by nuclear matrix protein ELISA, cell counts, and by Klenow labeling of DNA fragments. Epo and Epo-R mRNA were expressed in mixed primary cultures of neural tissues and NT2 and hNT cells. Epo was detected by ELISA in media removed from mixed cell cultures, and immunohistochemical staining confirmed the presence of Epo-R on neurons and their supporting cells. Semiquantitative PCR revealed no significant change in expression of either Epo or Epo-R in spinal cords between 7 and 16 wk of gestation, with increased expression of Epo and Epo-R in brains from 8 to 24 wk of gestation. Epo mRNA expression from neurons doubled under conditions of hypoxia. Recombinant Epo decreased apoptotic cell death of neurons under conditions of hypoxia. Protein and mRNA for Epo and its receptor are expressed by human neurons and glial cells in spinal cord and brain during fetal development. These receptors appear to have a neuroprotective effect in conditions of hypoxia.

Immunocytochemical method for investigating in vivo neuronal oxygen radical-induced lipid peroxidation.

The investigation of oxygen radical-induced lipid peroxidative neuronal damage in the context of acute and chronic neurodegenerative disorders has been largely limited to the use of ex vivo analytical methodologies. These are often fraught with sensitivity or specificity problems, or they are indirect. Furthermore, none of the analytical methods allow precise anatomical identification of the cells that are undergoing peroxidative injury. This paper describes an immunocytochemical method for localization of central nervous system (CNS) lipid peroxidation (LP) that employs a rabbit-derived antibody raised against malondialdehyde (MDA)-modified rabbit serum albumin (RSA). MDA is a breakdown product of peroxidized membrane polyunsaturated fatty acids that avidly binds to cellular proteins. Using the anti-MDA-RSA, we herein illustrate increased MDA-derived immunostaining: (1) in the spinal cord of transgenic familial amyotrophic lateral sclerosis (ALS) mice; and (2) in the selectively vulnerable gerbil hippocampal CA1 region after a 5 min episode of forebrain ischemia and its relationship to the time course of neuronal degeneration.

Fatal disseminated cercopithecine herpesvirus 1 (herpes B infection in cynomolgus monkeys (Macaca fascicularis).

Two adult female cynomolgus monkeys (Macaca fascicularis) that had been housed together for 4 months died within 2 weeks of each other after brief illnesses. Monkey No. 1 presented with collapse, watery stool, and hypothermia and died overnight. Monkey No. 2 presented with dyspnea, nasal discharge, leukopenia, and hypoproteinemia and was euthanized after 2 days. Both animals had peritoneal effusions, massive necrosis of pharyngeal, esophageal, and gastric mucosa, and multifocal hepatic and pancreatic necrosis. Monkey No. 2 also had lingual ulcers and locally extensive necrosis of spleen, adrenal glands, and lymph nodes. Large numbers of eosinophilic intranuclear inclusion bodies were present in epithelial and syncytial cells adjoining the necrotic foci in Monkey No. 2 but were absent in Monkey No. 1. Monkey No. 1 seroconverted to cercopithecine herpesvirus 1 (CHV-1, commonly known as herpes B) in the month before death. CHV-1 was isolated from a sample of stomach from Monkey No. 2, and electron microscopy of liver from this animal demonstrated herpesvirus particles within hepatocytes. Both animals were seropositive for simian type D retrovirus, and the virus was cultured from the liver of Monkey No. 2. A diagnosis of disseminated CHV-1 infection was made, possibly occurring secondary to immunosuppression due to infection with simian type D retrovirus. Although a high percentage of cynomolgus monkeys are apparently infected with CHV-1, disseminated disease is rare. Because infection with CHV-1 in humans is associated with a high fatality rate, familiarity with the lesions of disseminated infection with this virus is important.

Experimental infection of cynomolgus monkeys with simian parvovirus.

Simian parvovirus is a recently discovered parvovirus that was first isolated from cynomolgus monkeys. It is similar to human B19 parvovirus in terms of virus genome, tropism for erythroid cells, and characteristic pathology in natural infections. Cynomolgus monkeys were infected with simian parvovirus to investigate their potential usefulness as an animal model of human B19 parvovirus. Six adult female cynomolgus monkeys were inoculated with purified simian parvovirus by the intravenous or intranasal route and monitored for evidence of clinical abnormalities; this included the preparation of complete hematological profiles. Viremia and simian parvovirus-specific antibody were determined in infected monkeys by dot blot and Western blot assays, respectively. Bone marrow was examined at necropsy 6, 10, or 15 days postinfection. All of the monkeys developed a smoldering, low-grade viremia that peaked approximately 10 to 12 days after inoculation. Peak viremia coincided with the appearance of specific antibody and was followed by sudden clearance of the virus and complete, but transient, absence of reticulocytes from the peripheral blood. Clinical signs were mild and involved mainly anorexia and slight weight loss. Infection was associated with a mild decrease in hemoglobin, hematocrit, and erythrocyte numbers. Bone marrow showed marked destruction of erythroid cells coincident with peak viremia. Our findings indicate that infection of healthy monkeys by simian parvovirus is self-limited and mild, with transient cessation of erythropoiesis. Our study has reproduced Koch's postulates and further shown that simian parvovirus infection of monkeys is almost identical to human B19 parvovirus infection of humans. Accordingly, this animal model may prove valuable in the study of the pathogenesis of B19 virus infection.

MAP2 expression in the developing human fetal spinal cord and following xenotransplantation.

Human fetal spinal cord (FSC) tissue was obtained from elective abortions at 6-14 wk gestational age (GA). The specimens were then either immediately processed for immunohistochemical analysis or xenotransplantation. In the latter case, donor tissue was prepared as a dissociated cell suspension and then introduced either subpially or intraspinally into contusion lesions of the adult rat midthoracic spinal cord. The xenografts were subsequently examined by conventional histological and immunohistochemical methods at 2-3 mo postgrafting. Immunostaining showed that MAP2 was expressed heavily in cells residing in the mantle layer of the human fetal spinal cord in situ as early as 6 wk GA. Subpial and intraparenchymal xenografts also were intensely immunoreactive for MAP2, but no staining of surrounding host neural tissue was detected. We conclude that the differential expression of MAP2 can be used to distinguish human graft tissue from the surrounding rat spinal cord in this xenograft paradigm. Under appropriate staining conditions, MAP2 can thus serve to facilitate analyses of host-graft integration, donor cell migration, and neuritic outgrowth.

Posttranscriptional regulation of Caulobacter flagellin genes by a late flagellum assembly checkpoint.

Flagellum formation in Caulobacter crescentus requires ca. 50 flagellar genes, most of which belong to one of three classes (II, III, or IV). Epistasis experiments suggest that flagellar gene expression is coordinated with flagellum biosynthesis by two assembly checkpoints. Completion of the M/S ring-switch complex is required for the transition from class II to class III gene expression, and completion of the basal body-hook structure is required for the transition from class III to class IV gene expression. In studies focused on regulation of the class IV flagellin genes, we have examined fljK and fljL expression in a large number of flagellar mutants by using transcription and translation fusions to lacZ, nuclease S1 assays, and measurements of protein stability. The fljK-lacZ and fljL-lacZ transcription fusions were expressed in all class III flagellar mutants, although these strains do not make detectable 25- or 27-kDa flagellins. The finding that the fljK-lacZ translation fusion was not expressed in the same collection of class III mutants confirmed that fljK is regulated posttranscriptionally. The requirement of multiple class III genes for expression of the fljK-lacZ fusion suggests that completion of the basal body-hook is an assembly checkpoint for the posttranscriptional regulation of this flagellin gene. Deletion analysis within the 5' untranslated region of fljK identified a sequence between +24 and +38 required for regulation of the fljK-lacZ fusion by class III genes, which implicates an imperfect 14-bp direct repeat in the posttranscriptional regulation of fljK. Our results show that fljL is also regulated posttranscriptionally by class III and unclassified flagellar genes, apparently by a mechanism different from the one regulating fljK.

Endogenous repair after spinal cord contusion injuries in the rat.

Contusion injuries of the rat thoracic spinal cord were made using a standardized device developed for the Multicenter Animal Spinal Cord Injury Study (MASCIS). Lesions of different severity were studied for signs of endogenous repair at times up to 6 weeks following injury. Contusion injuries produced a typical picture of secondary damage resulting in the destruction of the cord center and the chronic sparing of a peripheral rim of fibers which varied in amount depending upon the injury magnitude. It was noted that the cavities often developed a dense cellular matrix that became partially filled with nerve fibers and associated Schwann cells. The amount of fiber and Schwann cell ingrowth was inversely related to the severity of injury and amount of peripheral fiber sparing. The source of the ingrowing fibers was not determined, but many of them clearly originated in the dorsal roots. In addition to signs of regeneration, we noted evidence for the proliferation of cells located in the ependymal zone surrounding the central canal at early times following contusion injuries. These cells may contribute to the development of cellular trabeculae that provide a scaffolding within the lesion cavity that provides the substrates for cellular infiltration and regeneration of axons. Together, these observations suggest that the endogenous reparative response to spinal contusion injury is substantial. Understanding the regulation and restrictions on the repair processes might lead to better ways in which to encourage spontaneous recovery after CNS injury.

Characteristics of human fetal spinal cord grafts in the adult rat spinal cord: influences of lesion and grafting conditions.

The present study evaluated the growth potential and differentiation of human fetal spinal cord (FSC) tissue in the injured adult rat spinal cord under different lesion and grafting conditions. Donor tissue at 6-9 weeks of gestational age was obtained through elective abortions and transplanted either immediately into acute resection (solid grafts) or into chronic contusion (suspension and solid grafts) lesions (i.e., 14-40 days after injury) in the thoracic spinal cord. The xenografts were then examined either histologically in plastic sections or immunocytochemically 1-3 months postgrafting. Intraspinal grafts in acute lesions demonstrated an 83% survival rate and developed as well-circumscribed nodules that were predominantly composed of immature astrocytes. Solid-piece grafts in chronic contusion lesions exhibited a 92% survival rate and also developed as nodular masses. These grafts, however, contained many immature neurons 2 months postgrafting. Suspension grafts in chronic contusion lesions had an 85% survival rate and expanded in a nonrestrictive, diffuse pattern. These transplants demonstrated large neuronally rich areas of neural parenchyma. Extensive neuritic outgrowth could also be seen extending from these grafts into the surrounding host spinal cord. These findings show that human FSC tissue reliably survives and differentiates in both acute and chronic lesions. However, both the lesion environment and the grafting techniques can greatly influence the pattern of differentiation and degree of host-graft integration achieved.