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J M Frade

Publications and source records attributed to J M Frade.

30 records · Page 2Linked to original sources
PubMed1997

Origin of eukaryotic programmed cell death: a consequence of aerobic metabolism?

A marked feature of eukaryotic programmed cell death is an early drop in mitochondrial transmembrane potential. This results from the opening of permeability transition pores, which are composed of adenine nucleotide translocators and mitochondrial porins. The latter share striking similarities with bacterial porins, including down-regulation of their pore size by purine nucleotides), suggesting a common origin. The porins of some invasive bacteria play a crucial role during their accommodation inside the host cell and this coexistence resembles the endosymbiotic origin of mitochondria. The above observations suggest that early in eukaryotic evolution, former invaders may have used porin-type channels to enter their host and to induce its death when the levels of its cytoplasmic purine nucleotides were dropped. The appearance of adenosine nucleotide translocators in the primitive eukaryotes, which permitted usage of the oxidative metabolism of the invaders, provided the basis for the permeability transition phenomena, now linked to the apoptotic process. Bcl-2-type molecules, being able to modulate the permeability transition pores by interaction with adenosine nucleotide translocators, may have played an essential role in conferring a means of controlling apoptosis.

Aerobiosis↗
PubMed1997

Control of early cell death by BDNF in the chick retina.

The developing chick retina undergoes at least two discrete periods of programmed cell death. The earlier period coincides with the main onset of neuron birth and migration (embryonic day 5-7), whereas the latter one corresponds to the well-documented process of retinal ganglion cell death following tectal innervation (embryonic day 10-14; Rager, G. H. (1980) Adv. Anat. Embryol. Cell Biol. 63, 1-92). In the early period, apoptosis is induced by nerve growth factor (NGF) acting via its p75 receptor (Frade, J. M., Rodríguez-Tébar, A. and Barde, Y.-A. (1996) Nature 383, 166-168). Here, we show that the application of brain-derived neurotrophic factor (BDNF) to chick embryos in ovo prevented retinal cell death in the early period, whereas exogenously applied NGF and neurotrophin-3 had no such effect. The addition of BDNF to embryos resulted in about 70% increase in the number of retinal ganglion cells in both E6 and E9 retinas relative to controls. BDNF is first expressed in both the pigment epithelium and neural retina of embryonic day 4 embryos, and at the same stage of development, its TrkB receptor is expressed in the neural retina. Our data indicate that early cell death is an important process in the neurogenesis of retinal ganglion cells and is regulated by locally produced BDNF.

Animals↗
PubMed1996

Enterotoxin septic shock protection and deficient T helper 2 cytokine production in growth hormone transgenic mice.

Neuroendocrine hormones have long been thought to play a role in lymphoid development and function. In particular, growth hormone has been shown to mediate thymic development as well as to promote T cell engraftment in severe combined immunodeficiency mice. Murine T helper cells are classified into two subsets based on their cytokine production pattern. Here, we report that transgenic mice for bovine growth hormone show significant alterations in T cell function and decreased capability for cytokine production, an effect that is more acute in T helper cells as measured by their inability to produce IL-4 upon in vivo injection with Staphylococcus aureus enterotoxin B. Furthermore, upon immunization with conventional Ags, growth hormone transgenic mice produce an altered Ig isotype pattern characterized by a response shift from IgG1 in nontransgenic mice to IgG2 in transgenic mice. The impaired T cell responses correlated with survival from septic shock mediated by bacterial enterotoxins. We conclude that growth hormone may have the potential of regulating immune responses in pathologic processes associated with hyperactivation of T cells or with massive cytokine production.

Animals↗
PubMed1996

Induction of cell death by endogenous nerve growth factor through its p75 receptor.

During development, neuronal survival is regulated by the limited availability of neurotrophins, which are proteins of the nerve growth factor (NGF) family. Activation of specific trk tyrosine kinase receptors by the neurotrophins blocks programmed cell death. The trkA-specific ligand NGF has also been shown to activate the non-tyrosine kinase receptor p75, a member of the tumour necrosis factor (TNF) receptor and Fas (APO-1/CD95) family. Here we report that, early in development, endogenous NGF causes the death of retinal neurons that express p75 but not trkA. These results indicate that, as with cells of the immune system, the death of neurons in the central nervous system can also be induced by ligands, and that the effect of NGF on cell fate depends on the type of receptor expressed by developing neurons.

Animals↗
PubMed1996

Neurotrophin-3 antibodies disrupt the normal development of the chick retina.

When chick embryos are treated with a monoclonal antibody specifically blocking the activity of neurotrophin-3 (NT-3), the development of the retina is profoundly affected. Fewer axons are found in the optic nerve, and the retina shows abnormalities in all layers. Early during retinogenesis, the proportion of dividing cells is higher in NT-3-deprived embryos compared with age-matched controls and that of differentiated neurons is smaller. The NT-3 receptor trkC is expressed early by a majority of retinal cells, and NT-3 is present in the retina at the earliest stage studied. Initially, it is located mainly in the pigmented epithelium, with a shift toward the neural retina as development proceeds. Thus, NT-3 seems to be an essential intrinsic signal acting early in development to promote the differentiation and survival of many retinal neurons.

Animals↗
PubMed1996

Laminin-1 selectively stimulates neuron generation from cultured retinal neuroepithelial cells.

Signals derived from the extracellular matrix (ECM) largely influence neuron differentiation and development. However, the action of specific ECM components in these processes is poorly understood. This had led us to investigate the role of different laminins in the survival, proliferation, and neuron differentiation of cultured neuroepithelial cells from the developing chicken retina. Dissociated retinal neuroepithelial cells from 5-day-old chicken embryos, cultured on laminin-1, survived, proliferated, and differentiated into neurons, as assessed by both [3H]-thymidine uptake and acquisition of neuronal markers. Nevertheless, these effects took place only in the presence of cell-cell contact. In contrast, RN22 Schwannoma-derived laminin (devoid of alpha 1 chain) and merosin (bearing an alpha 2 chain), which also promoted proliferation when cell-cell contact occurred, led to reduced cell survival and failed to foster neuron differentiation. Furthermore, the laminin-1 P1 fragment (containing the rod-like portions of the short arms of the molecule) also failed to support neuron generation. In contrast, the laminin-1 E8 fragment (containing the long arm of the molecule) supported such a process to the same extent as the whole laminin-1 molecule, although a similar activity cannot be ruled out in other globular domains of the short arms. However, these results stress the importance of the carboxy-terminal part of alpha 1 chain in neuronal development. A cDNA fragment of a chicken alpha 1 chain was cloned and semiquantitative PCR amplification revealed that its mRNA is expressed in retinal neuroepithelial cells at the time of neuron differentiation. Our data strongly suggest that an alpha 1-like chain-containing laminin is needed for differentiation of neuron precursor cells.

Amino Acid Sequence↗
PubMed1996

Insulin-like growth factor-I stimulates neurogenesis in chick retina by regulating expression of the alpha 6 integrin subunit.

Insulin-like growth factor I (IGF-I) strongly stimulates the generation of differentiated neurons in cultures of neuroepithelial cells of the embryonic chick neural retina in the presence of a laminin-1 tissue culture substrate. Treatment of cultured neuroepithelial cells with IGF-I rapidly up-regulated the mRNA coding for the alpha 6 integrin subunit whereas specific reduction of alpha 6 subunit levels by treatment with an alpha 6 integrin antisense oligonucleotide resulted in reduced neuronal differentiation in vitro. Although IGF-I immunoreactivity is seen throughout the neural retina, expression of IGF-I mRNA is confined to the pigment epithelium during the period of neurogenesis in vivo. Neutralization of the endogenous IGF-I with a blocking antibody down-regulated levels of alpha 6 integrin mRNA and reduced the production of differentiated retinal neurons in vivo. These data indicate a role for IGF-I in the generation of retinal neurons mediated by the interaction of laminin with its alpha 6 integrin subunit-containing receptor.

Animals↗
PubMed1995

Developmentally regulated vitronectin influences cell differentiation, neuron survival and process outgrowth in the developing chicken retina.

Vitronectin is a multifunctional protein involved in the regulation of the immune system and blood coagulation. Here we report that the expression of vitronectin is developmentally regulated in the embryonic retina of the chicken. Vitronectin immunoreactivity was detected in chicken retinas from embryonic day 5, encompassing the cell bodies of most neuroepithelial cells. At this developmental stage, alpha v integrin subunit expression was distributed across the retina, suggesting a ligand/receptor interaction. Expression of both vitronectin and alpha v increased during development and reached a maximum at embryonic day 9, a time when most differentiated neurons grow processes and initiate synapse formation. At this age, vitronectin immunoreactivity appeared to be located predominantly in the fiber and inner plexiform layers of the differentiated stratified retina. alpha v immunoreactivity and mRNA expression was seen associated with all layers formed by differentiated neurons, being most abundant in the ganglion cell and inner nuclear layers. Later in development, levels of vitronectin decreased and immunoreactivity appeared exclusively associated with the fiber layer. In accordance with this pattern of expression, vitronectin as a substrate sustained both proliferation and differentiation of cultured neuroepithelial cells from embryonic day 5 retinas. At later stages, vitronectin supported survival and neurite outgrowth of most differentiated neurons. Our data suggest that vitronectin is a ubiquitous component of the retinal extracellular matrix, serving as a substrate for developmental processes such as proliferation, differentiation of neuron progenitors, cell survival, and axonal and dendritic growth of differentiated neurons.

Animals↗
PubMed1994

Heterogeneity among neuroepithelial cells in the chick retina revealed by immunostaining with monoclonal antibody PM1.

Neuroepithelial cells appear as a homogeneous population of cells in the cell cycle that seem to behave as pluripotent neural precursors. The study of the intrinsic heterogeneity and subtle developmental changes among neuroepithelial cells has been hindered by the lack of specific markers. To address that study, a panel of monoclonal antibodies was produced against early developing chick retina. The monoclonal antibody precursor marker 1 (PM1) labels most, if not all, of the early neuroepithelial cells in embryonic day 4 retinal sections. This pattern is transient since the labelling becomes restricted to the peripheral retina as development proceeds and eventually disappears from the neuroepithelial cells. However, apparently in parallel, the differentiating retinal ganglion cells become PM1-positive. The expression of the PM1 antigen, a 73 x 10(3) M(r) protein, as shown by western blotting, also decreases with development. In addition, a chick retina dissociated-cell culture system, where retinal neuroepithelial cells actively proliferate and undergo differentiation under defined conditions, in combination with monoclonal antibody PM1, allowed us to characterize and quantify the proliferating and differentiating neuroepithelial cells. Interestingly, the fraction of total neuroepithelial cells that are stained with PM1 sharply decreases as retinal development proceeds, in correlation with the staining pattern in sections from matched stages. These data thus reveal that the pluripotent neural precursors in the chick retina already represent an intrinsically heterogeneous population, and that this population changes with development.

Animals↗
PubMed1994

Role of neurotrophins in the control of neural development: neurotrophin-3 promotes both neuron differentiation and survival of cultured chick retinal cells.

The effects of neurotrophins brain-derived neurotrophic factor and neurotrophin-3 on cultured dissociated cells from chick retina were studied at several embryonic ages from day 4 to day 13. Precursor cells from days 4-7 retinas proliferated in vitro and, after 20 h in culture, a proportion of them underwent spontaneous differentiation, as judged by both [3H]thymidine uptake and acquisition of neuronal morphology and neuron-specific markers. Brain-derived neurotrophic factor did not affect neuronal differentiation, although this factor supports survival of differentiated retinal ganglion cells [Rodríguez-Tébar et al. (1989) Devl Biol. 136, 296-303]. However, in cultures from young undifferentiated retinas, neurotrophin-3 produced up to a 2.5-fold increase in the number of [3H]thymidine-positive neurons, i.e. those that in vitro replicated their DNA. Moreover, in older retinas, neurotrophin-3, like brain-derived neurotrophic factor, supported the survival of differentiated retinal ganglion cells over a short developmental period. This effect was negligible at embryonic day 5, maximal at day 9, decreased at day 11 and was absent at embryonic day 13. Neurotrophin-3 also supported the survival of a population of amacrine neurons. This effect was modest at embryonic day 9, and increased at days 11 and 13. Our results show that, whereas the action of brain-derived neurotrophic factor is restricted to differentiated neurons, neurotrophin-3 exerts two distinct successive actions on retinal cells in vitro: first, this factor promotes either differentiation of neuroepithelial cells or maturation of recently differentiated neurons, and later in development, this factor supports the survival of differentiated retinal ganglion and amacrine cells but only during a discrete post-differentiation period.

Animals↗
PubMedDate not supplied

Neurotrophins and other growth factors in the generation of retinal neurons.

The generation of neurons in the vertebrate retina, as in other areas of the developing nervous system, largely depends on extracellular signals. Of the known signaling molecules, neurotrophins play decisive, defined, and distinct roles. The three neurotrophins identified in the chick, namely, neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF), are expressed in either the pigment epithelium (NT-3 and BDNF) or in the neural retina (NGF) at the onset of neuron birth. In addition, trkC and trkB, receptors for NT-3 and BDNF, respectively, together with p75, the low-affinity neurotrophin receptor, are expressed in the retina at the same developmental period. The role of these three neurotrophins in the differentiation of neurons in the chick retina has been elucidated by a combination of in vitro and in vivo experiments. Thus, NT-3 promotes the conversion of neuroepithelial cells into neurons, whereas BDNF and NGF control the programmed cell death (apoptosis) that affects early postmitotic neuroblasts. BDNF, acting via its trkB receptor, is a survival factor for these cells, whereas NGF, binding to p75 receptor, acts as a killing factor, thereby controlling the provisional number of newly generated neurons.

Animals↗