BMP4 is essential for lens induction in the mouse embryo

Vertebrate lens development is a classical model system for studying embryonic tissue interactions. Little is known, however, about the molecules mediating such inductive events. Here, we show that Bmp4, which is expressed strongly in the optic vesicle and weakly in the surrounding mesenchyme and surface ectoderm, has crucial roles during lens induction. In Bmp4(tm1) homozygous null mutant embryos, lens induction is absent, but the process can be rescued by exogenous BMP4 protein applied into the optic vesicle in explant cultures. This is associated with rescue of ectodermal expression of Sox2, an early lens placode marker. Substituting the optic vesicle in explant cultures with BMP4-carrying beads, however, does not lead to lens induction, indicating that other factors produced by the optic vesicle are involved. BMP4 appears to regulate expression of a putative downstream gene, Msx2, in the optic vesicle. No change in Pax6 expression is seen in Bmp4(tm1) mutant eyes, and Bmp4 expression appears unaffected in the eyes of homozygous Pax6(Sey-1Neu), suggesting that PAX6 and BMP4 function independently. Based on these results we propose that BMP4 is required for the optic vesicle to manifest its lens-inducing activity, by regulating downstream genes and/or serving as one component of multiple inductive signals.     

Brain-derived neurotrophic factor (BDNF) protects cultured rat cerebellar granule neurons against glucose deprivation-induced apoptosis

In the present study, cell death induced by glucose deprivation in primary cultures of cerebellar granule neurons was examined. Glucose deprivation-induced apoptotic cell death was demonstrated using the terminal transferase-mediated (TdT) deoxyuridine triphosphate (d-UTP)-biotin nick end labeling (TUNEL) method and DNA fragmentation assays. When the effects of different neurotrophins on the survival of cerebellar granule neurons after glucose deprivation were assessed, BDNF, but not NT-3 or NGF, was found to protect cerebellar granule neurons against glucose deprivation-induced cell death. In addition, BDNF treatment increased c-Fos immunoreactivity in the cerebellar granule neurons. These results are consistent with the hypothesis that neuronal death due to glucose deprivation has a significant apoptotic component and that neurotrophins can protect against hypoglycemic damage.     

Enteral glutamine supplementation for very-low-birth-weight infants decreases hospital costs

Vertebrate Pax-6 and its Drosophila homolog eyeless play central roles in eye specification, although it is not clear if this represents the ancestral role of this gene class. As the most "primitive" animals with true nervous systems, the Cnidaria may be informative in terms of the evolution of the Pax gene family. For this reason we surveyed the Pax gene complement of a representative of the basal cnidarian class (the Anthozoa), the coral Acropora millepora. cDNAs encoding two coral Pax proteins were isolated. Pax-Aam encoded a protein containing only a paired domain, whereas Pax-Cam also contained a homeodomain clearly related to those in the Pax-6 family. The paired domains in both proteins most resembled the vertebrate Pax-2/5/8 class, but shared several distinctive substitutions. As in most Pax-6 homologs and orthologs, an intron was present in the Pax-Cam locus at a position corresponding to residues 46/47 in the homeodomain. We propose a model for evolution of the Pax family, in which the ancestor of all of the vertebrate Pax genes most resembled Pax-6, and arose via fusion of a Pax-Aam-like gene (encoding only a paired domain) with an anteriorly-expressed homeobox gene resembling the paired-like class.     

Biofeedback improves functional outcome after sphincteroplasty

Pax genes are expressed in specific patterns in the nervous system during development and in the adult. Recent findings suggest a link between the expression of Pax-2 and axonal guidance. Mice with a targeted deletion of Pax-2 are an excellent tool for studying axonal pathfinding at the molecular level, especially with respect to the optic chiasm. The date reviewed here suggest that Pax-2 regulates the expression of surface molecules involved in contact attraction and that the mutual regulation of the expression of Pax-2 and the Sonic hedgehog gene is of importance in the formation of the chiasm region.     

NT-3 has a tropic effect on process outgrowth by postnatal auditory neurones in vitro

CONFOCAL analysis of early postnatal auditory neurones in a bicompartmental culture system was used to test for chemoattractant properties of NGF, BDNF and NT-3 on neuronal process outgrowth. NT-3 exerted a strong tropic effect on neuritic outgrowth from auditory neurones in this system. BDNF and NGF did not have any tropic activity that directed processes outgrowth from auditory neurones. However, BDNF was important for the support of neuronal survival in NGF-treated cultures and for neuritogenesis in NT-3-treated cultures. Since NT-3 has been identified as both a survival factor and a chemotropic agent for auditory neurones, it is likely that this neurotrophin will be a useful therapeutic agent in the treatment of damaged cochleae for the recovery of hearing.     

Time-dependent changes in neurotrophic factor mRNA expression after kindling and long-term potentiation in rats

We compared the time-dependent changes in messenger ribonucleic acid (mRNA) levels for two neurotrophic factors after amygdala-kindled seizures and hippocampal long-term potentiation (LTP) in rats in vivo. The brain-derived neurotrophic factor (BDNF) mRNA levels in the bilateral granule cell layer of the dentate gyrus, increased significantly 1-4 h after stage 5 kindled seizures. Nerve growth factor (NGF) mRNA levels increased throughout the bilateral limbic regions more gradually than those of BDNF mRNA. The maximum levels in the dentate gyrus ipsilateral to stimulation (BDNF mRNA: 493%, NGF mRNA: 199% of control levels) occurred 2 h after seizures. As observed with kindling, BDNF and NGF mRNA expression increased in the dentate gyrus ipsilateral to stimulation also increased following LTP induced by the perforant path stimulation, with maximum levels occurring 2 h and 4 h, respectively, after stimulation, when they reached 284% and 189% of the control levels, respectively. These results suggest that BDNF and NGF are involved in enhancement of synaptic efficacy in the granule cells of the dentate gyrus in the hippocampus in kindling, not related to the neuronal excitability associated with seizure activity.     

Neurotrophin effects on survival and expression of cholinergic properties in cultured rat septal neurons under normal and stress conditions

These studies tested the hypothesis that survival-promoting effects of neurotrophins on basal forebrain cholinergic neurons are enhanced under stress. Septal neurons from embryonic day 14-15 rats exposed for 10-14 d to neurotrophin [nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or neurotrophin-4 (NT-4), each at 100 ng/ml] showed a two- to threefold increase in choline acetyltransferase (ChAT) activity, with little evidence of synergistic interactions. Neurotrophins produced no significant increase in the survival of total or acetylcholinesterase (AChE)-positive neurons at moderate plating density (1200-1600 cells/mm2). However, with very low plating densities (2-28 cells/mm2) BDNF, NT-3, and NT-4 (but not NGF) increased total neuronal survival, and BDNF increased survival of AChE-positive neurons. NGF and BDNF enhanced ChAT activity and survival of cholinergic neurons after a 24 hr hypoglycemic stress, even when added 1 hr after stress onset. All four tested neurotrophins increased total neuronal survival after hypoglycemic stress. These results suggest that neurotrophins are important for preservation of central cholinergic function under stress conditions, with different neurotrophins protecting against different stresses. The stress-associated survival-promoting effects of neurotrophins were not limited to the cholinergic subpopulation.     

Neurotrophins regulate sequential changes in neurotrophin receptor expression by sympathetic neuroblasts

We have examined the mechanisms controlling the induction of the two NGF receptors, trkA and p75, in proliferating neuroblasts immuno-isolated from thoracolumbar embryonic sympathetic ganglia. Contrary to prior studies, we find that induction of p75 follows rather than precedes that of trkA; this late induction is consistent with the fact that p75 functions at relatively late stages of sympathetic development. trkA induction is apparently not controlled by a cell-intrinsic mechanism. Rather, this receptor is induced by environmental signals including NT-3, which also acts as an interim survival factor for these neuroblasts. trkA induction by NT-3 is consequent to its promotion of mitotic arrest, as anti-mitotic drugs also efficiently induce trkA. p75 expression is induced in trkA-expressing cells by NGF. Thus, the development of sympathetic neurons involves sequential actions of different neurotrophins, which also regulate the expression of their own and each other's receptors.     

Developmental cues modulate GABAA receptor subunit mRNA expression in cultured cerebellar granule neurons

The developmental expression of mRNAs encoding the GABAA receptor was analyzed in the rat cerebellar cortex and in cultured cerebellar granule neurons. Our studies in vivo reveal that the alpha 1-, beta 2-, and gamma 2-subunit mRNA levels in the cerebellar cortex rise dramatically during the second post-natal week, a period temporally correlated with extensive cerebellar maturation. To determine if these increases were preprogrammed or dependent on extrinsic factors, we examined subunit mRNA expression in granule cell cultures prepared at embryonic day 19 (E19) and postnatal day 10 (P10), immature and mature stages of cerebellar development, respectively. In E19 cultures, the alpha 1, beta 2, and gamma 2 GABAA receptor subunit mRNAs were present and their levels remained constant over the 21 d culture period. These results suggest that GABAA receptor gene expression is not intrinsic to the immature granule cells. A different pattern was found in P10 cultures where the three subunit mRNAs were initially present at levels approximately sixfold higher than those found at E19. The beta 2- and gamma 2-subunit mRNAs remained constant for 4 d and then increased sixfold between 4 and 7 d in culture. The magnitude and time course of these increases were similar to the developmental changes that occurred in vivo. Thus, our findings raise the possibility that signals encountered during development are necessary to induce GABAA receptor subunit mRNA expression. Moreover, these cues have been received by granule neurons prior to P10.(ABSTRACT TRUNCATED AT 250 WORDS)