Search PubMed⌕ Search

Biomedical subjects

K F Lee

Publications and source records attributed to K F Lee.

At least 91 records · Page 5Linked to original sources
PubMed1996

Cell death in the Schwann cell lineage and its regulation by neuregulin.

The development of Schwann cells, the myelin-forming glial cells of the vertebrate peripheral nervous system, involves a neonatal phase of proliferation in which cells migrate along and segregate newly formed axons. Withdrawal from the cell cycle, around postnatal days 2-4 in rodents, initiates terminal differentiation to the myelinating state. During this time, Schwann cell number is subject to stringent regulation such that within the first postnatal week, axons and myelinating Schwann cells attain the one-to-one relationship characteristic of the mature nerve. The mechanisms that underly this developmental control remain largely undefined. In this report, we examine the role of apoptosis in the determination of postnatal Schwann cell number. We find that Schwann cells isolated from postnatal day 3 rat sciatic nerve undergo apoptosis in vitro upon serum withdrawal and that Schwann cell death can be prevented by beta forms of neuregulin (NRG-beta) but not by fibroblast growth factor 2 or platelet-derived growth factors AA and BB. This NRG-beta-mediated Schwann cell survival is apparently transduced through an ErbB2/ErbB3 receptor heterodimer. We also provide evidence that postnatal Schwann cells undergo developmentally regulated apoptosis in vivo. Together with other recent findings, these results suggest that Schwann cell apoptosis may play an important role in peripheral nerve development and that Schwann cell survival may be regulated by access to axonally derived NRG.

Animals↗
PubMed1996

Overproduction, purification and characterization of M.EcoHK31I, a bacterial methyltransferase with two polypeptides.

The two overlapping genes coding for EcoHK31I methyltransferase have previously been cloned, sequenced and expressed [Lee, Kam and Shaw (1995) Nucleic Acids Res. 23, 103-108]. Here we describe protocols developed to purify polypeptides alpha and beta together or separately, to apparent homogeneity by various chromatographic media. M.EcoHK31I is a heterodimer with a native molecular mass of 61 kDa. Its specific activity towards non-methylated lambda DNA was 3.0 x 10(5) units per mg of protein. The respective denatured molecular masses of polypeptides alpha and beta were 38 and 23 kDa, and their pI values were 8.7 and 6.8. Initial rate kinetic parameters of the native enzyme were 2.0 nM, 0.58 microM and 3 min-1 for KmDNA, KmAdoMet and kcat. respectively, where AdoMet stands for S-adenosyl-L-methionine. Fully active enzyme was reconstituted by co-purifying the two separately synthesized polypeptides, and activity assays confirmed our previous finding that two polypeptides were needed to methylate substrate DNA.

Amino Acid Sequence↗
PubMed1996

Long-term functional status and mortality of elderly patients with severe closed head injuries.

OBJECTIVE: To evaluate long-term clinical outcome of elderly patients with severe closed head injuries. DESIGN: Retrospective study. PATIENTS AND METHODS: All patients older than 65 years of age admitted to a regional trauma center with a diagnosis of closed head injury and an admission Glasgow Coma Scale (GCS) score of 8 or less. Using chi 2 analysis, Student's t test, and multiple logistic regression, we correlated age, sex, mechanism of injury, pupillary reactivity, alcohol and drug use, admission GCS score, Injury Severity Score, Revised Trauma Score, heart rate, and blood pressure to the main outcome measures, i.e. long-term functional outcome and mortality. RESULTS: Among 40 elderly patients who met the criteria, 27% were still alive at the end of 38 +/- 3 month follow-up. Eighty-five percent of patients who were discharged from the hospital were still alive long-term, but did not show significant neurologic improvement. In a univariate analysis, GCS and pupillary reactivity were predictive for long-term functional outcome and mortality. In a multivariate analysis, GCS and heart rate were predictive. All patients with an admission GCS score of 3 died in-hospital. All patients with an admission GCS score of 3 to 7 were either deceased or lived in persistent vegetative or dependent functional states. CONCLUSIONS: Elderly patients with severe closed head injuries have high in-hospital mortality. Those who survived the hospital stay had high long-term survival, but did not show significant functional improvement. Prediction of long-term functional status is vital to the trauma care of elderly patients with severe closed head injuries.

Age Distribution↗
PubMed1996

Prenatal and postnatal requirements of NT-3 for sympathetic neuroblast survival and innervation of specific targets.

Postnatal homozygous neurotrophin-3 mutant mice display a loss of about half the sympathetic superior cervical ganglion (SCG) neurons (Ernfors, P., Lee, K.-F., Kucera, J. and Jaenisch, R. (1994a) Cell 77, 503-512; Farinas, I., Jones, K. R., Backus, C., Wang, X. Y. and Reichardt, L. F. (1994) Nature 369, 658-661). We found that this loss is caused by excessive apoptosis of sympathetic neuroblasts leading to a failure to generate a normal number of neurons during neurogenesis. NT-3 was also found to be required postnatally. In Nt-3-/- mice, sympathetic fibers failed to invade pineal gland and external ear postnatally; whereas other targets of the external and internal carotid nerves, including the submandibular gland and the iris, displayed a normal complement of sympathetic innervation. Sympathetic fibers of mice carrying one functional copy of the Nt-3 gene (Nt-3+/- mice) invaded the pineal gland, but failed to branch and form a ground plexus. Cultured neonatal sympathetic neurons responded to NT-3 by neurite outgrowth and mRNA upregulation of the NT-3 receptor, trkC. Exogenously administered NT-3 promoted sympathetic growth and rescued the sympathetic target deficit of the mutant mice. We conclude that NT-3 is required for the survival of sympathetic neuroblasts during neurogenesis and for sympathetic innervation and branching in specific targets after birth.

Aging↗
PubMed1995

Requirement for neuregulin receptor erbB2 in neural and cardiac development.

The receptor erbB2/neu is a member of the epidermal growth factor receptor (EGFR or erbB) family that also includes erbB3 and erbB4. Amplification of the erbB2/neu gene is found in many cancer types and its overexpression is correlated with a poor prognosis for breast and ovarian cancer patients. Investigation of the biology of erbB2 led to the identification of a family of ligands termed neuregulins which included the neu-differentiation factors, the heregulins, a ligand with acetylcholine-receptor-inducing activity and glial growth factor. Several lines of evidence suggest that heterodimerization of erbB2 with other erbB receptors is required for neuregulin signalling. Here we investigate the developmental role of erbB2 in mammalian development in mice carrying an erbB2 null allele. We find that mutant embryos die before E11, probably as a result of dysfunctions associated with a lack of cardiac trabeculae. Development of cranial neural-crest-derived sensory ganglia was markedly affected. DiI retrograde tracing revealed that the development of motor nerves was also compromised. Our results demonstrate the importance of erbB2 in neural and cardiac development.

Animals↗
PubMed1995

A bacterial methyltransferase M.EcoHK311 requires two proteins for in vitro methylation.

The genes encoding EcoHK311 restriction-modification (R-M) system were isolated from a clinically-isolated Escherichia coli strain HK31. The entire R-M system of EcoHK311 is located in a 2.1 kb fragment. R.EcoHK311 is an isoschizomer of Eael which recognizes and cleaves Y decreases GGCCR. M.EcoHK31l consists of two polypeptides alpha and beta with sizes 309 and 176 aa, respectively. Polypeptide beta is encoded within aa, alternative reading frame of polypeptide alpha. All the conserved motifs in mC5-MTases can be found in polypeptide alpha except motif IX which is present in polypeptide beta. Polypeptides alpha and beta were separately synthesized in a T7 promoter controlled over-expression system and in vitro methylation occurred only when the two extracts were mixed and thus confirms that two polypeptides are required for methylation.

Amino Acid Sequence↗
PubMed1995

Differential role of the low affinity neurotrophin receptor (p75) in retrograde axonal transport of the neurotrophins.

The receptor mechanisms mediating the retrograde axonal transport of the neurotrophins have been investigated in adult rats. We show that transport of the TrkB ligands NT-4 and BDNF to peripheral neurons is dependent on the low affinity neurotrophin receptor (LNR). Pharmacological manipulation of LNR in vivo using either an anti-LNR antibody or a soluble recombinant LNR extracellular domain completely blocked retrograde transport of NT-4 and BDNF to sensory neurons, while having minimal effects on the transport of NGF in either sensory or sympathetic neurons. Furthermore, in mice with a null mutation of LNR, the transport of NT-4 and BDNF, but not NGF, was dramatically reduced. These observations demonstrate a selective role for LNR in retrograde transport of the various neurotrophins from distinct target regions in vivo.

Animals↗
PubMed1995

Fatal intra-cranial haemorrhage in 2 cases of beta-thalassaemia major.

Spontaneous intracranial haemorrhage is one of the cerebrovascular complications in beta-thalassaemia major patients. This is a report of 2 cases of fatal intracranial haemorrhage. Their ages were 12 and 7 years respectively, and they had been receiving regular blood transfusion for the past 3 and 2 years respectively. They developed acute onset of headache, loss of consciousness and convulsions at 5 and 2 days respectively after their last blood transfusion. C-T scan of the brain showed massive intracranial haemorrhage with extension into the ventricles. The spontaneous intracranial haemorrhages in these two cases was probably multi-factorial in origin. The predisposing factors included recent blood transfusion, prolonged prothrombin time and partial thromboplastin time as well as reduced platelet count.

Cerebral Hemorrhage↗
PubMed1995

Studies on the physiological role of brain-derived neurotrophic factor and neurotrophin-3 in knockout mice.

Brain-derived neurotrophic factor and neurotrophin-3 deficient mice were generated by gene targeting. The analysis of these mice has led to the characterization of their role in the survival of neurons in the peripheral nervous system. NT-3 deficient mice displayed severe movement defects and most died shortly after birth. The mutation causes loss of substantial portions of cranial and spinal peripheral sensory and sympathetic neurons. Significantly, spinal proprioceptive afferents and their peripheral sense organs (muscle spindles and Golgi tendon organs) were completely absent in homozygous mutant mice. BDNF deficient mice displayed deficiencies in coordination and balance. Excessive loss of neurons was detected in most of the peripheral sensory ganglia examined, but the survival of sympathetic neurons was not affected. The most marked reduction of neurons was observed in the vestibular ganglion, leading to a loss of innervation of the sensory epithelia of the vestibular compartments of the inner ear.

Afferent Pathways↗
PubMed1994

Lack of neurotrophin-3 leads to deficiencies in the peripheral nervous system and loss of limb proprioceptive afferents.

Neurotrophin-3-deficient (NT-3-deficient) mice were generated by gene targeting. Mutant mice displayed severe movement defects of the limbs, and most died shortly after birth. Substantial portions of peripheral sensory and sympathetic neurons were lost while motor neurons were not affected. Significantly, spinal proprioceptive afferents and their peripheral sense organs (muscle spindles and Golgi tendon organs) were completely absent in homozygous mutant mice. This correlated with a loss of parvalbumin and carbonic anhydrase-positive neurons in the dorsal root ganglion. No gross abnormalities were seen in Pacinian corpuscles, cutaneous afferents containing substance P and calcitonin gene-related peptide, and deep nerve fibers in the joint capsule and tendon. Importantly, the number of muscle spindles in heterozygous mutant mice was half of that in control mice, indicating that NT-3 is present at limiting concentrations in the embryo.

Animals↗
PubMed1994

Dependence on p75 for innervation of some sympathetic targets.

The low-affinity neurotrophin receptor p75 binds all neurotrophins with similar affinity. For elucidation of its function, mice bearing a null mutation in the p75 locus were generated. Examination of sympathetic innervation of target tissues revealed that pineal glands lacked innervation and sweat gland innervation was absent or reduced in particular footpads. The absence of adult innervation reflects the failure of axons to reach these targets during development rather than a target deficit. These results indicate that p75 facilitates development of specific populations of sympathetic neurons, for which it may support axon growth.

Adrenergic Fibers↗
PubMed1994

Mice lacking brain-derived neurotrophic factor develop with sensory deficits.

During vertebrate development, neuronal survival depends on target-derived neurotrophic factors. Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, can prevent the death of particular peripheral sensory neurons in vitro, and of central motor neurons as well as dopaminergic and cholinergic neurons of the basal forebrain during development. It also prevents the death of motor neurons and midbrain dopaminergic neurons induced by lesions. Here we show that mutant mice lacking BDNF have severe deficiencies in coordination and balance, associated with excessive degeneration in several sensory ganglia including the vestibular ganglion. The few remaining vestibular axons fail to contact the vestibular sensory epithelia, and terminate in the adjacent connective tissue. Survival of sympathetic, midbrain dopaminergic and motor neurons is not affected. These results indicate that BDNF is required for the survival and target innervation of particular neuronal populations.

Animals↗
PubMed1994

Activin/inhibin beta B subunit gene disruption leads to defects in eyelid development and female reproduction.

Inhibins and activins are dimeric growth factors of the transforming growth factor-beta superfamily, a class of peptides that can regulate the growth and differentiation of a variety of cell types. Recently, activins have been implicated in early vertebrate development through their ability to evoke, in Xenopus embryo explants, both morphological and molecular changes characteristic of mesoderm induction. To understand these processes further, we have used homologous recombination in embryonic stem cells to create mouse strains carrying mutations in the gene encoding the activin/inhibin beta B subunit. These mice are expected to be deficient in activin B (beta B:beta B), activin AB (beta A:beta B), and inhibin B (alpha:beta B). Viable mutant animals were generated, indicating that the beta B subunit is not essential for mesoderm formation in the mouse. Mutant animals suffered, however, from distinct developmental and reproductive defects. An apparent failure of eyelid fusion during late embryonic development led to eye lesions in mutant animals. Whereas beta B-deficient males bred normally, mutant females manifested a profoundly impaired reproductive ability, characterized by perinatal lethality of their offspring. The phenotype of mutant mice suggests that activin beta B (1) plays a role in late fetal development and (2) is critical for female fecundity. In addition, we have found that expression of the related beta A subunit of activin is highly upregulated in ovaries of mutant females. Altered regulation of beta A activin in beta B-deficient mice may contribute to the mutant phenotype.

Activins↗
PubMed1994

p75-deficient embryonic dorsal root sensory and neonatal sympathetic neurons display a decreased sensitivity to NGF.

To understand the role of low-affinity neurotrophin receptor p75 in neural development, we previously generated mice carrying a null mutation in the p75 locus (Lee, K. F., Li, E., Huber, L. J., Landis, S. C., Sharpe, A. H., Chao, M. V. and Jaenisch, R. (1992) Cell 69, 737-749). To elucidate the mechanisms leading to deficits in the peripheral nervous system in p75 mutant mice, we have employed dissociated cultures to examine the responses of p75-deficient dorsal root ganglion (DRG) and superior cervical ganglion (SCG) neurons to different neurotrophins. We found that p75-deficient DRG and SCG neurons displayed a 2- to 3-fold decreased sensitivity to NGF at embryonic day 15 (E15) and postnatal day 3 (P3), respectively, ages that coincide with the peak of naturally occurring cell death. Furthermore, while p75-deficient E15 DRG neurons did not change their response specificity to BDNF, NT-3, and NT-4/5, P3 SCG neurons became more responsive to NT-3 at higher concentrations (nanomolar ranges). These results may help explain the deficits in the peripheral nervous system in p75 mutant mice and provide evidence that p75 can modulate neurotrophin sensitivity in some neurons.

Animals↗
PubMed1994

Anatomy and physiology of the pleural space.

The pleural cavity is created between the 4th and 7th week of embryologic development and is lined by the splanchnopleurae and somatopleurae. These embryonic components of visceral and parietal pleurae develop different anatomic characteristics with regard to vascular, lymphatic, and nervous supply. Both pleurae have two layers: a superficial mesothelial cell layer facing the pleural space and an underlying connective tissue layer. Various ultrastructures of the pleura show a close relationship to the basic functions of the pleural membranes, such as local inflammatory response and maintenance of the pleural fluid. The latter function is especially important in the mechanical coupling of the lung and chest wall. The fluid in the pleural space transmits transpleural forces involved in normal respiration, and the maintenance of the optimal volume and thickness is regulated closely. Fluid is filtered into the pleural space according to the net hydrostaticoncotic pressure gradient. It flows downward along a vertical pressure gradient, presumably determined by hydrostatic pressure and resistance to viscous flow. There also may be a net movement of fluid from the costal pleura to the mediastinal and interlobar regions. In these areas, pleural fluid is resorbed primarily through lymphatic stomata on the parietal pleural surface.

Connective Tissue↗