Essential roles for the FE65 amyloid precursor protein-interacting proteins in brain development

Targeted deletion of two members of the FE65 family of adaptor proteins, FE65 and FE65L1, results in cortical dysplasia. Heterotopias resembling those found in cobblestone lissencephalies in which neuroepithelial cells migrate into superficial layers of the developing cortex, aberrant cortical projections and loss of infrapyramidal mossy fibers arise in FE65/FE65L1 compound null animals, but not in single gene knockouts. The disruption of pial basal membranes underlying the heterotopias and poor organization of fibrillar laminin by isolated meningeal fibroblasts from double knockouts suggests that FE65 proteins are involved in basement membrane assembly. A similar phenotype is observed in triple mutant mice lacking the APP family members APP, APLP1 and APLP2, all of which interact with FE65 proteins, suggesting that this phenotype may be caused by decreased transmission of an APP-dependent signal through the FE65 proteins. The defects observed in the double knockout may also involve the family of Ena/Vasp proteins, which participate in actin cytoskeleton remodeling and interact with the WW domains of FE65 proteins.     

Essential function in chloroplast recognition of the ferredoxin transit peptide processing region

Summary Plant ferredoxin is a nuclear-encoded chloroplast protein that is synthesized in the cytoplasm as a transit peptide-containing precursor molecule. To identify functional regions in the pre-ferredoxin transit peptide we constructed mutants with deletions of increasing length from the processing site toward the amino-terminus of the precursor. The mutant proteins were tested in an in vitro chloroplast binding and import assay. Deletion of the amino acids adjacent to the processing site completely abolishes binding and import. This region contains a sequence motif that is conserved among different precursor species. By constructing and testing mutants in the amino-terminal region of the mature part of the precursor protein, we found that this region of the molecule can greatly influence the import reaction.     

Essential function in chloroplast recognition of the ferredoxin transit peptide processing region

Molecular Genetics and Genomics - Plant ferredoxin is a nuclear-encoded chloroplast protein that is synthesized in the cytoplasm as a transit peptide-containing precursor molecule. To identify...     

Hormonal control of neural function in the adult brain

Although the mechanisms by which peripheral hormones modulate complex behaviors are far from being well understood, recent advances in deciphering the mechanisms of hormone action in the brain are promising. Current areas of interest include the molecular mechanisms of steroid receptor action, the steroid modulation of synaptic function, and the mediation of steroid-regulated neuronal and glial plasticity by growth factors or proteins associated with brain development.     

The brain within the tumor: new roles for axon guidance molecules in cancers

Slits, semaphorins and netrins are three families of proteins that can attract or repel growing axons and migrating neurons in the developing nervous system of vertebrates and invertebrates. Recent studies have shown that they are widely expressed outside the nervous system and that they may play important roles in cancers. Several of the genes encoding these proteins are localized on chromosomal region associated with frequent loss-of-heterozygosity in tumors and cancer cell lines and there is also significant hypermethylation of their promoter suggesting that they may act as tumor suppressors. In addition, proteins in all these families and their receptors appear to control the vascularization of the tumors. Last, many axon guidance molecules also regulate cell migration and apoptosis in normal and tumorigenic tissues. Overall, this suggests that molecules that could mimick or block the activity of axon guidance molecules may be used as therapeutic agents for the treatment of malignancy.     

Essential roles of mitochondrial and heme function in lung cancer bioenergetics and tumorigenesis

Contrary to Warburg’s hypothesis, mitochondrial oxidative phosphorylation (OXPHOS) contributes significantly to fueling cancer cells. Several recent studies have demonstrated that radiotherapy-resistant and chemotherapy-resistant cancer cells depend on OXPHOS for survival and progression. Several cancers exhibit an increased risk in association with heme intake. Mitochondria are widely known to carry out oxidative phosphorylation. In addition, mitochondria are also involved in heme synthesis. Heme serves as a prosthetic group for several proteins that constitute the complexes of mitochondrial electron transport chain. Therefore, heme plays a pivotal role in OXPHOS and oxygen consumption. Further, lung cancer cells exhibit heme accumulation and require heme for proliferation and invasion in vitro. Abnormalities in mitochondrial biogenesis and mutations are implicated in cancer. This review delves into mitochondrial OXPHOS and lesser explored area of heme metabolism in lung cancer.     

Quantitative analysis of the roles of IRM cell adhesion molecules in column formation in the fly brain

The Drosophila visual center shows columnar structures, basic structural and functional units of the brain, that are shared with the mammalian cerebral cortex. Visual information received in the ommatidia in the compound eye is transmitted to the columns in the brain. However, the developmental mechanisms of column formation are largely unknown. The Irre Cell Recognition Module (IRM) proteins are a family of immunoglobulin cell adhesion molecules. The four Drosophila IRM proteins are localized to the developing columns, the structure of which is affected in IRM mutants, suggesting that IRM proteins are essential for column formation. Since IRM proteins are cell adhesion molecules, they may regulate cell adhesion between columnar neurons. To test this possibility, we specifically knocked down IRM genes in columnar neurons and examined the defects in column formation. We developed a system that automatically extracts the individual column images and quantifies the column shape. Using this system, we demonstrated that IRM genes play critical roles in regulating column shape in a core columnar neuron, Mi1. We also show that their expression in the other columnar neurons, Mi4 and T4/5, is essential, suggesting that the interactions between IRM proteins and multiple neurons shape the columns in the fly brain.     

神经细胞粘附分子结构特征和生理功能

神经细胞粘附分子是一类调节细胞与细胞、细胞与细胞外基质间粘附作用的膜表面糖蛋白,主要有NCAM-180、NCAM-140、NCAM-120三种形式,多与PSA结合在一起。在神经系统中,NCAM的表达具有时间和空间特异性,最主要的作用为调节神经系统的可塑性,这种作用可能是通过PSA-NCAM对AMPA的调节作用,主要是通过调节蛋白激酶的表达和细胞内Ca^2 浓度来实现的。     

Expression and function of cell adhesion molecules during neural crest migration

Neural crest cells are highly migratory cells that give rise to many derivatives including peripheral ganglia, craniofacial structures and melanocytes. Neural crest cells migrate along defined pathways to their target sites, interacting with each other and their environment as they migrate. Cell adhesion molecules are critical during this process. In this review we discuss the expression and function of cell adhesion molecules during the process of neural crest migration, in particular cadherins, integrins, members of the immunoglobulin superfamily of cell adhesion molecules, and the proteolytic enzymes that cleave these cell adhesion molecules. The expression and function of these cell adhesion molecules and proteases are compared across neural crest emigrating from different axial levels, and across different species of vertebrates.     

Alcohol exposure alters the expression pattern of neural cell adhesion molecules during brain development

Neural cell adhesion molecules (NCAMs) play critical roles during development of the nervous system. The aim of this study is to investigate the possible effect of ethanol exposure on the pattern of expression and sialylation of NCAM isoforms during postnatal rat brain development because alterations in NCAM content and distribution have been associated with defects in cell migration, synapse formation, and memory consolidation, and deficits in these processes have been observed after in utero alcohol exposure. The expression of NCAM isoforms in the developing cerebral cortex of pups from control and alcohol-fed mothers was assessed by western blotting, ribonuclease protection assay, and immunocytochemistry. The highly sialylated form of NCAM [polysialic acid (PSA)-NCAM] is mainly expressed during the neonatal period and then is down-regulated in parallel with the appearance of NCAM 180 and NCAM 140. Ethanol exposure increases PSA-NCAM levels during the neonatal period, delays the loss of PSA-NCAM, decreases the amount of NCAM 180 and NCAM 140 isoforms, and reduces sialyltransferase activity during postnatal brain development. Neuraminidase treatment of ethanol-exposed neonatal brains leads to more intense band degradation products, suggesting a higher content of NCAM polypeptides carrying PSA in these samples. However, NCAM mRNA levels are not changed by ethanol. Immunocytochemical analysis demonstrates that ethanol triggers an increase in PSA-NCAM immunolabeling in the cytoplasm of astroglial cells, accompanied by a decrease in immunogold particles over the plasma membrane. These findings indicate that ethanol exposure during brain development alters the pattern of NCAM expression and suggest that modification of NCAM could affect neuronal-glial interactions that might contribute to the brain defects observed after in utero alcohol exposure.     

Essential roles of the Fas-associated death domain in autoimmune encephalomyelitis

The Fas-associated death domain (FADD) protein mediates apoptosis by coupling death receptors with the caspase cascade. Paradoxically, it also promotes cell mitosis through its C-terminal region. Apoptosis and mitosis are opposing processes that can have radically different consequences. To determine which of the FADD effects prevails in T cell-mediated autoimmune diseases, we studied myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) using mice that express a dominant-negative FADD (FADD-DN) transgene in the T cell lineage. We found that FADD blockade in T cells prevented the development of autoimmune encephalomyelitis and inhibited both Th1 and Th2 type responses. Myelin oligodendrocyte glycoprotein-specific T cell proliferation was also dramatically reduced in FADD-DN mice despite the resistance of T cells to activation-induced cell death. These results indicate that although FADD expressed by T cells is involved in regulating both mitosis and apoptosis, its effect on mitosis prevails in EAE, and that strategies inhibiting FADD functions in T cells could be effective in preventing the disease.     

The different roles of metal ions and water molecules in the recognition and catalyzed hydrolysis of ATP by phenanthroline-containing polyamines

The phenanthroline bridging polyaza ligands L1, L2 and L3 can selectively and strongly bind nucleotides at physiological pH, and hence accelerate the hydrolysis rate of the bound ATP. It is interesting that a phosphoramidate intermediate at 2.88 ppm (should be added 5.63 ppm when compared with other models) was found in the hydrolysis process of L/ATP. By introduction of metal ions (critical Zn(2+) or hard Mg(2+), Ca(2+)) to the L/ATP system, recognition of the anionic substrates by the protonated ligands was greatly promoted. However, due to the different affinities of metal ions to the receptor and the substrate, ATP hydrolysis in Zn(2+)/L/ATP system and Mg(2+)(Ca(2+))/L/ATP system occurs through different mechanisms. By comparison with the M/ATP (M=Zn(2+), Mg(2+), Ca(2+)) system, the rates of ATP-hydrolysis in the Mg(2+)Ca(2+)/L/ATP system and the Zn(2+)/L/ATP system were enhanced and retarded, respectively. Moreover, the reasons contributing to large rate range of the L/ATP systems and M(2+)/L/ATP systems were given. The results show that metal ions vertically regulate the recognition and hydrolysis of ATP. On the other hand, water molecule participates in the hydrolysis reactions at different steps with different functions in the L/ATP systems and M(Zn(2+), Mg(2+), Ca(2+))L/ATP systems.     

Three distinct roles of aquaporin-4 in brain function revealed by knockout mice

Aquaporin-4 (AQP4) is expressed in astrocytes throughout the central nervous system, particularly at the blood-brain and brain-cerebrospinal fluid barriers. Phenotype analysis of transgenic mice lacking AQP4 has provided compelling evidence for involvement of AQP4 in cerebral water balance, astrocyte migration, and neural signal transduction. AQP4-null mice have reduced brain swelling and improved neurological outcome in models of (cellular) cytotoxic cerebral edema including water intoxication, focal cerebral ischemia, and bacterial meningitis. However, brain swelling and clinical outcome are worse in AQP4-null mice in models of vasogenic (fluid leak) edema including cortical freeze-injury, brain tumor, brain abscess and hydrocephalus, probably due to impaired AQP4-dependent brain water clearance. AQP4 deficiency or knock-down slows astrocyte migration in response to a chemotactic stimulus in vitro, and AQP4 deletion impairs glial scar progression following injury in vivo. AQP4-null mice also manifest reduced sound- and light-evoked potentials, and increased threshold and prolonged duration of induced seizures. Impaired K⁺ reuptake by astrocytes in AQP4 deficiency may account for the neural signal transduction phenotype. Based on these findings, we propose modulation of AQP4 expression or function as a novel therapeutic strategy for a variety of cerebral disorders including stroke, tumor, infection, hydrocephalus, epilepsy, and traumatic brain injury.     

Three distinct roles of aquaporin-4 in brain function revealed by knockout mice

Aquaporin-4 (AQP4) is expressed in astrocytes throughout the central nervous system, particularly at the blood-brain and brain-cerebrospinal fluid barriers. Phenotype analysis of transgenic mice lacking AQP4 has provided compelling evidence for involvement of AQP4 in cerebral water balance, astrocyte migration, and neural signal transduction. AQP4-null mice have reduced brain swelling and improved neurological outcome in models of (cellular) cytotoxic cerebral edema including water intoxication, focal cerebral ischemia, and bacterial meningitis. However, brain swelling and clinical outcome are worse in AQP4-null mice in models of vasogenic (fluid leak) edema including cortical freeze-injury, brain tumor, brain abscess and hydrocephalus, probably due to impaired AQP4-dependent brain water clearance. AQP4 deficiency or knock-down slows astrocyte migration in response to a chemotactic stimulus in vitro, and AQP4 deletion impairs glial scar progression following injury in vivo. AQP4-null mice also manifest reduced sound- and light-evoked potentials, and increased threshold and prolonged duration of induced seizures. Impaired K+ reuptake by astrocytes in AQP4 deficiency may account for the neural signal transduction phenotype. Based on these findings, we propose modulation of AQP4 expression or function as a novel therapeutic strategy for a variety of cerebral disorders including stroke, tumor, infection, hydrocephalus, epilepsy, and traumatic brain injury.     

Adult human brain expresses four different molecular forms of neural cell adhesion molecules

Using antibodies to rat neural cell adhesion molecules (NCAM), we analyzed the NCAM of adult human brain. Various regions of the brain were analyzed quantitatively by Western blot. Grey matter showed four bands of NCAM with apparent molecular weights of 180,000, 170,000, 140,000 and 120,000. White matter showed one major band with an apparent M_r of 120,000 and a minor band of 180,000. Cerebellar grey matter contained mainly 170,000, 140,000 and 120,000, white cerebellar white matter had only 180,000 and 120,000 M₁ NCAMS. Spinal cord showed mainly 120,000 M_r NCAM. Deglycosylation using N-glycanase resulted in 170,000, 160,000, 130,000 and 110,000 M_r proteins, suggesting that the four forms of human NCAM are derived from individual polypeptides. The presence of 170,000 M₁ NCAM is unique to human brain.     

肌苷促进脑损伤后神经功能恢复的实验研究

目的：中枢损伤是目前致残率最高的疾病之一,肌苷对于神经损伤后功能恢复的促进作用已经成为研究热点,本研究拟建立一侧前肢瘫痪的大鼠脑外伤模型,证实肌苷治疗促进中枢损伤后上肢功能恢复的有效性,同时初步探索其机制。方法：建立一侧运动皮层冲击损毁的大鼠模型,通过肢体不对称实验、抓取实验等行为学观察证实其惠侧上肢功能受损,后在实验组进行肌苷药物14天,观察28天内上肢功能的恢复情况,与对照组作对比。证实其行为学上的有效性,同时对损伤侧大脑进行顺行BDA染色,探索其内在机制。结果：通过28天的观察发现经过肌苷治疗的的实验组大鼠肢体不对称实验、抓取实验等行为学评分明显好于隐性对照组,顺行BDA染色证实其有促进损伤周围健存皮层突触再生和代偿的作用。结论：肌苷可以促进中枢损伤后大鼠残存神经元得突触再生,使其大脑能在最大程度上代偿其丧失的功能,该药物可能会成为一种新的中枢损伤治疗的前体药物。     

肌苷促进脑损伤后神经功能恢复的实验研究

目的:中枢损伤是目前致残率最高的疾病之一,肌苷对于神经损伤后功能恢复的促进作用已经成为研究热点,本研究拟建立一侧前肢瘫痪的大鼠脑外伤模型,证实肌苷治疗促进中枢损伤后上肢功能恢复的有效性,同时初步探索其机制。方法:建立一侧运动皮层冲击损毁的大鼠模型,通过肢体不对称实验、抓取实验等行为学观察证实其患侧上肢功能受损,后在实验组进行肌苷药物14天,观察28天内上肢功能的恢复情况,与对照组作对比,证实其行为学上的有效性,同时对损伤侧大脑进行顺行BDA染色,探索其内在机制。结果:通过28天的观察发现经过肌苷治疗的的实验组大鼠肢体不对称实验、抓取实验等行为学评分明显好于隐性对照组,顺行BDA染色证实其有促进损伤周围健存皮层突触再生和代偿的作用。结论:肌苷可以促进中枢损伤后大鼠残存神经元得突触再生,使其大脑能在最大程度上代偿其丧失的功能,该药物可能会成为一种新的中枢损伤治疗的前体药物。