Multiple levels of Notch signal regulation (review).

Notch is a vitally important signalling receptor controlling cell fate determination and pattern formation in numerous ways during development of both invertebrate and vertebrate species. An intriguing pathway for the Notch signal has emerged where, after ligand-dependent proteolysis, an intracellular fragment of the receptor itself translocates to the nucleus to regulate gene expression. The nuclear activity of the Notch intracellular domain is linked to complexes regulating chromatin organization through histone deacetylation and acetylation. To allow the Notch signal to be deployed in numerous contexts, many different mechanisms have evolved to regulate the level, duration and spatial distribution of Notch activity. Regulation occurs at multiple levels including patterns of ligand and receptor expression, Notch-ligand interactions, trafficking of the receptor and ligands, and covalent modifications including glycosylation, phosphorylation and ubiquitination. Several Notch regulatory proteins have conserved domains that link them to the ubiquitination pathway, and ubiquitination of the Notch intracellular domain has recently been linked to its degradation. Different proteolytically derived isoforms of Notch have also been identified that may be involved in alternative Notch-dependent signals or regulatory mechanisms, and differences between the four mammalian Notch homologues are beginning to be appreciated.

DrhoGEF3 encodes a new Drosophila DH domain protein that exhibits a highly dynamic embryonic expression pattern.

The Rho GTPases regulate many different cellular and developmental processes, and activation of Rho GTPase signalling is mediated through interaction with the Dbl homology (DH) protein domain. We describe the expression pattern of DrhoGEF3 (cytological position 61B1-B3), which encodes a new member of the DH domain protein family from Drosophila and is a homologue of the human protein hPEM-2. During gastrulation and germ band extension, DrhoGEF3 exhibits a segmented expression pattern. DrhoGEF3 is subsequently expressed in the visceral mesoderm, at the sites of muscle attachment and in specific groups of sub-epidermal cells. The possible function of such a dynamically expressed signalling molecule is discussed.

Drosophila dumpy is a gigantic extracellular protein required to maintain tension at epidermal-cuticle attachment sites.

BACKGROUND: Growth and morphogenesis during development depend both on patterning genes, which assign positional information, and on genes that regulate mechanical forces. The dumpy gene of the fruit fly Drosophila melanogaster is an example of the latter class, with mutant phenotypes affecting size and shape of the limbs, thoracic cuticle, trachea and mouthparts. RESULTS: The genetically complex dumpy locus was found to span over 100 kb and encode a gigantic 2.5 MDa extracellular matrix protein. Dumpy represents an extreme form of modular protein evolution, containing 308 epidermal growth factor (EGF) modules, interspersed with a new module class, DPY, and terminating in a crosslinking zona pellucida domain and membrane anchor sequence. We determined the three-dimensional structure of the DPY module by nuclear magnetic resonance (NMR) spectroscopy and found that it forms a disulphide-stabilised beta sheet motif, capable of linking end-to-end with EGF modules to form a fibre. Consistent with its cuticle phenotypes, dumpy is expressed at several sites of cuticle-epidermal cell attachment, including the trachea and the muscle tendon cells, which mediate anchorage of the muscles to the cuticle. CONCLUSIONS: The dumpy gene encodes a gigantic extracellular molecule that we predict to be a membrane-anchored fibre of almost a micrometer in length. Insertion and crosslinking of this fibre within the cuticle may provide a strong anchor for the underlying tissue, allowing it to maintain mechanical tension at sites under stress. This would explain its contribution to tissue morphogenesis through its regulation of mechanical properties.

Plexiform fibrohistiocytic tumor of the foot.

The first case of plexiform fibrohistiocytic tumor in the foot is presented in this article. The tumor developed on the dorsum of the left foot in a 14-year-old female. This tumor was originally described in 1988 by Enzinger and Zhang. Their study indicated that this tumor has a female predominance, median age of 14.5 years, 63% located in the upper extremities, 37.5% recurrence rate, and 3% metastasis rate. These tumors are very unique with a nodular pattern and a cellular component of histiocytes, fibroblasts, and multinucleated giant cells. Typically they are located within the deep dermis and subcutaneous tissue. Immunohistochemical preparations show that the tumor does not stain for S-100 protein, desmin, cytokeratin, factor VIII-related protein, or lysozyme. However, it does stain for alpha-1-antitrypsin, alpha-1-antichymotrypsin, alpha-smooth muscle-specific actin, vimentin, and CD68 antibody.

Mutations in shaking-B prevent electrical synapse formation in the Drosophila giant fiber system.

The giant fiber system (GFS) is a simple network of neurons that mediates visually elicited escape behavior in Drosophila. The giant fiber (GF), the major component of the system, is a large, descending interneuron that relays visual stimuli to the motoneurons that innervate the tergotrochanteral jump muscle (TTM) and dorsal longitudinal flight muscles (DLMs). Mutations in the neural transcript from the shaking-B locus abolish the behavioral response by disrupting transmission at some electrical synapses in the GFS. This study focuses on the role of the gene in the development of the synaptic connections. Using an enhancer-trap line that expresses lacZ in the GFs, we show that the neurons develop during the first 30 hr of metamorphosis. Within the next 15 hr, they begin to form electrical synapses, as indicated by the transfer of intracellularly injected Lucifer yellow. The GFs dye-couple to the TTM motoneuron between 30 and 45 hr of metamorphosis, to the peripherally synapsing interneuron that drives the DLM motoneurons at approximately 48 hr, and to giant commissural interneurons in the brain at approximately 55 hr. Immunocytochemistry with shaking-B peptide antisera demonstrates that the expression of shaking-B protein in the region of GFS synapses coincides temporally with the onset of synaptogenesis; expression persists thereafter. The mutation shak-B2, which eliminates protein expression, prevents the establishment of dye coupling shaking-B, therefore, is essential for the assembly and/or maintenance of functional gap junctions at electrical synapses in the GFS.

Essential and neural transcripts from the Drosophila shaking-B locus are differentially expressed in the embryonic mesoderm and pupal nervous system.

The shaking-B gene of Drosophila encodes two functions: one specifically neural and the other required for viability. Flies carrying neural mutations show a range of defects, the best characterized of which is a disruption of some synapses in the giant fibre system, while mutations in the essential function cause animals to die as first instar larvae. We have characterised an essential transcript from this locus and show that mutant lesions underlying two lethal shaking-B alleles map to its coding sequence. We also propose a new model for the topologies of Shaking-B proteins and their relatives. Essential shaking-B transcripts are found in embryonic mesodermal derivatives, while during metamorphosis both essential and neural transcripts are dynamically expressed in the pupal nervous system. Although the expression patterns of these transcripts overlap in many cells, only the neural form is expressed in the giant fibre cell bodies and the lamina and medulla of the optic lobes. This observation correlates with the phenotypes of mutations which disrupt the coding region of this neural transcript. On the basis of the expression patterns of shaking-B transcripts and the phenotypes conferred by mutations of shaking-B and homologous genes, we suggest that Shaking-B proteins and their homologues may be involved in the organisation of cellular membranes.

Ontogeny of renal hemodynamic response to renal nerve stimulation in sheep.

The renal hemodynamic response to direct electrical stimulation of renal nerves was studied in conscious and chronically instrumented fetal (130-142 days gestation; term 145 days), newborn (7-12 days postnatal), and adult nonpregnant sheep. Renal nerve stimulation (RNS) produced a significant decrease in renal blood flow (RBF) velocity and a significant increase in renal vascular resistance (RVR) in all three groups of animals. The overall decline in RBF velocity and the overall rise in RVR was less pronounced in fetal than in adult sheep (P less than 0.05). Changes in RBF velocity and RVR using an RNS frequency of 16 Hz were -35 +/- 4 and 81 +/- 19% in fetal sheep, -61 +/- 10 and 374 +/- 128% in newborn lambs, and -84 +/- 12 and 540 +/- 94% in adult sheep, respectively. RNS during intrarenal infusion of the alpha-adrenoceptor antagonist phentolamine was associated with a significant increase in RBF velocity and decrease in RVR in both fetal sheep and newborn lambs, but not in adult sheep. Moreover, it was found that the rise in RBF velocity and the decrease in RVR associated with RNS during alpha-adrenoceptor antagonism were completely inhibited by intrarenal infusion of ICI 118,551, a beta 2-adrenoceptor antagonist and unaffected by either cholinergic or dopaminergic antagonists. Taken together, these results suggest that the overall renal vasoconstrictor response to RNS is age dependent. Furthermore, the present results demonstrate that, contrary to observations made in adult animals, RNS can produce renal vasodilation in immature animals that is mediated by beta 2-adrenoceptors.

Linguistic background and test material considerations in assessing sentence identification ability in English- and Spanish-English-speaking adolescents.

This study investigated the influence of linguistic background differences on sentence identification by groups of English- and Spanish-English-speaking adolescents. Subjects were required to identify recorded meaningful and nonmeaningful (synthetic) sentences presented in a white noise background using a closed message set-response format. The results indicate that linguistic background variables significantly influence sentence identification ability and that these variables are not adequately controlled for by a closed message set. A significant difference in the ability to identify meaningful and nonmeaningful sentences was revealed. Contrary to previous indications, synthetic sentence identification appeared to be contingent upon key work or phrase recognition.