Requirement of Drosophila NF1 for activation of adenylyl cyclase by PACAP38-like neuropeptides

Neurofibromin modulation of ras activity is required for normal endocardial-mesenchymal transformation in the developing heart

Endocardial cushions are the precursors of the cardiac valves and form by a process of epithelial-mesenchymal transformation. Secreted growth factors from myocardium induce endocardial cells to transform into mesenchyme and invade the overlying extracellular matrix. Here, we show that the product of the Nf1 neurofibromatosis gene is required to regulate this event. In the absence of neurofibromin, mouse embryo hearts develop overabundant endocardial cushions due to hyperproliferation and lack of normal apoptosis. Neurofibromin deficiency in explant cultures is reproduced by activation of ras signaling pathways, and the Nf1(−/−) mutant phenotype is prevented by inhibiting ras in vitro. These results indicate that neurofibromin normally acts to modulate epithelial-mesenchymal transformation and proliferation in the developing heart by down regulating ras activity.

Ionic currents in normal and neurofibromatosis type 1-affected human Schwann cells: induction of tumor cell K current in normal Schwann cells by cyclic AMP

Comparisons were made of whole cell voltage clamp recordings from cultures of normal Schwann cells (SC) from three human subjects and from three neurofibrosarcoma cell lines. The whole cell K+ (K) currents of normal and tumor cells could be divided into three types based on voltage activation range, pharmacology, and macroscopic inactivation: A type current, tetraethylammonium- (TEA-) only-sensitive current, and inward rectifier current. The most conspicuous difference between normal and tumor cells was the nature of K currents present. Normal SC K currents were inactivating, A type currents blocked by extracellular 4-aminopyridine (4-AP; 5 mM). The whole cell K currents of tumor cells were noninactivating due to the presence of non-inactivating A current, or non-inactivating, TEA-only sensitive current, or both, despite the presence of inactivating A current in some tumor cells. TEA-only-sensitive currents, which were 4-AP-insensitive and noninactivating, were common in all three tumor cell lines, but were not observed in normal SC. Inward rectifier K currents were a conspicuous feature of two of the tumor cells lines but were rarely observed in whole cell recordings of normal SC. The properties of Na+ currents recorded in both normal and tumor cells were not significantly different. Treatment of normal SC with a membrane-permeant analog of cyclic AMP (cAMP) resulted in functional expression of the TEA-only-sensitive K currents typical of tumor cells. These results establish the abnormal ion channel profile of neurofibromatosis type 1 (NF1)-tumor cells and suggest (Guo et al.: Science 276:795-798, 1997) that regulation of ionic currents by second messengers may involve the NF1 gene.

Gene discovery in Drosophila: new insights for learning and memory

Genetic approaches have been used to investigate increasingly complex biological systems. Here we review the current state of genetic analysis of learning and memory in the fruitfly, Drosophila melanogaster. Emerging findings support two main themes. First, discovery and manipulation of genes involved with behavioral plasticity in genetically accessible systems such as D. melanogaster enables dissection of the biochemical, cellular, anatomical, and behavioral pathways of learning and memory. Second, because core cellular mechanisms of simple forms of learning are evolutionarily conserved, biological pathways discovered in invertebrates are likely to be conserved in vertebrate systems as well.

Genetic analysis of synaptic development and plasticity: homeostatic regulation of synaptic efficacy

When experimentally challenged with perturbations in synaptic structure and function, neurons have the remarkable ability to regulate their synaptic efficacy back to the normal range. Recent genetic analysis has provided insights into the mechanisms controlling this form of synaptic homeostasis, with implications for our understanding of synaptic development and plasticity.

Rescue of a Drosophila NF1 mutant phenotype by protein kinase A

The neurofibromatosis type 1 (NF1) tumor suppressor protein is thought to restrict cell proliferation by functioning as a Ras-specific guanosine triphosphatase-activating protein. However, Drosophila homozygous for null mutations of an NF1 homolog showed no obvious signs of perturbed Ras1-mediated signaling. Loss of NF1 resulted in a reduction in size of larvae, pupae, and adults. This size defect was not modified by manipulating Ras1 signaling but was restored by expression of activated adenosine 3', 5'-monophosphate-dependent protein kinase (PKA). Thus, NF1 and PKA appear to interact in a pathway that controls the overall growth of Drosophila.