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Cytokines of the TGF beta superfamily regulate many aspects of cellular function by activating receptor complexes consisting of two distantly related serine/threonine kinases. Previous studies have indicated that Drosophila dpp uses similar signaling complexes and strictly requires the punt and thick veins receptors to transduce the signal across the membrane. Here, we show that the schnurri (shn) gene is required for many aspects of dpp signaling. Genetic epistasis experiments indicate that shn functions downstream of the dpp signal and its receptors. The shn gene encodes a large protein similar to a family of mammalian zinc finger transcription factors. The shn protein might therefore act as a nuclear target in the dpp signaling pathway directly regulating the expression of dpp-responsive genes.

TGF beta elicits diverse cellular responses by signaling through receptor complexes formed by two distantly related transmembrane serine/threonine kinases called type II and type I receptors. Previous studies have indicated that the product of the Drosophila thick veins (tkv) gene is a type I receptor for decapentaplegic (dpp). Here, we show that the Drosophila gene punt encodes a homolog of a vertebrate type II receptor, and we demonstrate that punt, like tkv, is essential in vivo for dpp-dependent patterning processes. Because no dpp-related signalling is apparent in the absence of either the punt or tkv receptor, we infer that both receptors act in concert to transduce the dpp signal and that their functions cannot be replaced by the other extant type II and I receptors.

Differentiation of distinct cell types at specific locations within a developing organism depends largely on the ability of cells to communicate. A major class of signalling proteins implicated in cell to cell communication is represented by members of the TGF beta superfamily. A corresponding class of transmembrane serine/threonine kinases has recently been discovered that act as cell surface receptors for ligands of the TGF beta superfamily. The product of the Drosophila gene decapentaplegic (dpp) encodes a TGF beta homolog that plays multiple roles during embryogenesis and the development of imaginal discs. Here we describe the complex expression pattern of thick veins (tkv), which encodes a receptor for dpp. We make use of tkv loss-of-function mutations to examine the consequences of the failure of embryonic cells to respond to dpp and/or other TGF beta homologs. We find that while maternal tkv product allows largely normal dorsoventral pattering of the embryo, zygotic tkv activity is indispensable for dorsal closure of the embryo after germ band retraction. Furthermore, tkv activity is crucial for patterning the visceral mesoderm; in the absence of functional tkv gene product, visceral mesoderm parasegment 7 cells fail to express Ultrabithorax, but instead accumulate Antennapedia protein. The tkv receptor is therefore involved in delimiting the expression domains of homeotic genes in the visceral mesoderm. Interestingly, tkv mutants fail to establish a proper tracheal network. Tracheal braches formed by cells migrating in dorsal or ventral directions are absent in tkv mutants. The requirements for tkv in dorsal closure, visceral mesoderm and trachea development assign novel functions to dpp or a closely related member of the TGF beta superfamily.

Members of the TGF beta superfamily of secreted signaling molecules regulate growth and cellular patterning during development and interact with specific type I and type II membrane receptors possessing a cytoplasmic serine/threonine kinase domain. We describe two members of the type I receptor family in Drosophila and demonstrate that they are encoded by the genes saxophone (sax) and thick veins (tkv). Further, we show that mutations that abolish sax or tkv activity cause phenotypes similar to partial or complete loss of activity, respectively, of the TGF beta homolog decapentaplegic (dpp). We propose that specification of distinct cell fates in response to different concentrations of dpp may be achieved combinatorially by the sax and tkv receptors.

Drosophila limbs are subdivided into anterior and posterior compartments which derive from adjacent cell populations founded early in development. Evidence is now provided that posterior cells organize growth and cell patterning in both compartments by secreting hedgehog protein and that hedgehog protein acts indirectly by inducing neighbouring anterior cells to secrete decapentaplegic or wingless protein.

The cellular functions of the Drosophila src 64B (Dsrc) gene product, Dsrc, and of most vertebrate Src-family kinases, are unknown. We have examined the effects of over-expression of wild type and mutated forms of Dsrc in transgenic Drosophila. Expression of both wild type Dsrc and a C-terminally truncated mutant at high levels during embryonic development induced extensive tyrosine phosphorylation of cellular proteins and caused considerable lethality, correlating with a block to germ-band retraction. Over-expression in the eye imaginal disc led to excess production of photoreceptor cells in the adult ommatidia. In contrast, expression of a kinase-inactive form of Dsrc caused distinct nervous system abnormalities in embryos and decreased the numbers of photoreceptor cells in the adult eye ommatidia. This suggests that active forms of Dsrc alter development by phosphorylation. Both the lethality and the eye roughening caused by activated Dsrc were partially suppressed by mutations in the Drosophila Ras1 gene. These results suggest that over-expressed Dsrc may function through Ras1 to stimulate differentiation in the embryonic nervous system and eye imaginal disc, and that kinase-active Dsrc interferes with these processes.

Distinct cell types differentiate along the dorsoventral axis of the neural tube. We have cloned and characterized a novel member of the TGF beta gene family, dorsalin-1 (dsl-1), that appears to regulate cell differentiation within the neural tube. dsl-1 is expressed selectively in the dorsal neural tube, and its pattern of expression appears to be restricted by early signals from the notochord. Exposure of neural plate cells to dsl-1 promotes the differentiation of cells with neural crest-like properties and inhibits the induction of motor neurons by signals from the notochord and floor plate. These findings suggest that dsl-1 regulates the differentiation of cell types along the dorsoventral axis of the neural tube, acting in conjunction with distinct ventralizing signals from the notochord and floor plate.

The adult appendages of Drosophila are formed from imaginal discs, sheets of epithelial cells that proliferate during larval development and differentiate during metamorphosis. wingless (wg, DWnt-1) protein, a putative signaling molecule, is expressed only in prospective ventral cells in each of the leg discs. To test the role of wg, we have generated randomly positioned clones of cells that express wg protein constitutively. Clones that arise in the prospective ventral portions of the leg discs develop normally. In contrast, dorsally situated clones give rise to ventrolateral patterns and exert a ventralizing influence on neighboring wild-type tissue. We propose that wg protein organizes leg pattern along the dorsoventral axis by conferring ventral positional information within the disc.

This study describes the structure and function of pox neuro (poxn), a gene previously isolated by virtue of a conserved domain, the paired box, which it shares with the segmentation genes paired and gooseberry. Its expression pattern has been analyzed, particularly during development of the PNS. We propose that poxn is a "neuroblast identity" gene acting in both the PNS and the CNS on the basis of the following evidence. Its expression is restricted to four neuronal precursors in each hemisegment: two neuronal stem cells (neuroblasts) in the CNS, and two sensory mother cells (SMCs) in the PNS. The SMCs that express poxn produce the poly-innervated external sense organs of the larva. In poxn- embryos, poly-innervated sense organs are transformed into mono-innervated. Conversely, ectopic expression of poxn in embryos transformed with a heat-inducible poxn gene can switch mono-innervated to poly-innervated sense organs. Expression of poxn in the wing disc is restricted to the SMCs of the poly-innervated sense organs, suggesting that poxn also determines the lineage of poly-innervated adult sense organs.

Determination of cell fate in the developing eye of Drosophila depends on a precise sequence of cellular interactions which generate the stereotypic array of ommatidia. In the eye imaginal disc, an initially unpatterned epithelial sheath of cells, the first step in this process may be the specification of R8 photoreceptor cells at regular intervals. Genes such as Notch and scabrous, known to be involved in bristle development, also participate in this process, suggesting that the specification of ommatidial founder cells and the formation of sensory organs in the adult epidermis may involve a similar mechanism, that of lateral inhibition. The subsequent steps of ommatidial assembly, following R8 assignment, involve a different mechanism: Undetermined cells read their position based on the contacts they make with neighbors that have already begun to differentiate. The development of the R7 photoreceptor cell, one of the eight photoreceptor cells in the ommatidium, is best understood. An important role seems to be played by sevenless, a receptor tyrosine kinase on the surface of the R7 precursor. It transmits the positional information--most likely encoded by the boss protein on the neighboring R8 cell membrane--into the cell via its tyrosine kinase, which activates a signal transduction cascade. Constitutive activation of the sevenless kinase by overexpression of an N-terminally truncated form results in the diversion of other ommatidial cells into the R7 pathway suggesting that activation of the sevenless signalling pathway is sufficient to specify R7 development. Genetic dissection of this pathway should therefore identify components of a signalling cascade activated by a tyrosine kinase.

Cell fate in the developing eye is determined by a cascade of inductive interactions. In this process, the sevenless protein--a receptor tyrosine kinase--is required for the specification of the R7 photoreceptor cell fate. We have constructed a gain-of-function sevenless mutation (SevS11) by overexpressing a truncated sevenless protein in the cells where sevenless is normally expressed. In SevS11 mutant flies, all sevenless-expressing cells initiate neural development. This results in the formation of multiple R7-like photoreceptors per ommatidium. Therefore, sevenless activity appears to be necessary and sufficient for the determination of R7 cell fate. These results illustrate the central role receptor tyrosine kinases can play in the specification of cell fate during development.

Determination of cell fate in the developing eye of Drosophila depends on cellular interactions. In the eye imaginal disc, an initially unpatterned epithelial sheath of cells, single cells are specified in regular intervals to become the R8 photoreceptor cells. Genes such as Notch and scabrous participate in this process suggesting that specification of ommatidial founder cells and the formation of bristles in the adult epidermis involve a similar mechanism known as lateral inhibition. The subsequent steps of ommatidial assembly involve a different mechanism: undetermined cells read their position based on the contacts they make with neighbors that have already begun to differentiate. The development of the R7 photoreceptor cell is best understood. The key role seems to be played by sevenless, a receptor tyrosine kinase on the surface of the R7 precursor. It transmits the positional information--most likely encoded by boss on the neighboring R8 cell membrane--into the cell via its tyrosine kinase that activates a signal transduction cascade. Two components of this cascade--Sos and sina--have been identified genetically. sina encodes a nuclear protein whose expression is not limited to R7. Constitutive activation of the sevenless kinase by overexpression results in the diversion of other ommatidial cells into the R7 pathway, suggesting that activation of the sevenless signalling pathway is sufficient to specify R7 development.

In the developing eye of Drosophila, the homeo box gene rough is required in the developing photoreceptor cells R2 and R5 for the correct development of the neighboring R3 and R4 cells. We have expressed rough ectopically in a limited subset of developing ommatidial cells using the sevenless enhancer. Expression of rough in the presumptive R7 cell transforms this cell into an R1-6 type photoreceptor. This transformation is cell autonomous in contrast to the apparent nonautonomy of the rough mutant phenotype and depends on the presence of the sevenless gene. We propose that in wild type, rough functions autonomously in the specification of R2/5 photoreceptor cell identity but by itself cannot initiate neural development.

In the developing eye of Drosophila cell fate is controlled by a cascade of inductive interactions. Little is known about how the specificity of positional signalling is achieved such that directly adjacent progenitor cells reproducibly choose distinct developmental pathways. The determination of the R7 photoreceptor in each ommatidium depends on the presence of the sevenless protein which acts as a receptor for positional information on the R7 precursor. The rough gene encodes a homeodomain protein that plays an instructive role in the determination of the R3 and R4 photoreceptor cells. The use of ectopic expression of sevenless and rough has provided insight into the mechanisms of positional signalling and the normal function of rough. Ubiquitous expression of sevenless does not alter cell fate suggesting that the inducing signal is both spatially and temporally controlled. Conversely, ectopic expression of rough in the R7 precursor causes a transformation of R7 cells into R1-6 type cells. This indicates that rough acts, similar to other homeobox genes, as a selector gene that determines the fate of single cells.

In vertebrates, a tyrosine kinase activity has been identified as an integral component of growth factor receptors and the products of proto-oncogenes. Many of these receptor tyrosine kinases (RTKs) appear to play a key role in the regulation of cell growth. Recent analyses of several Drosophila genes encoding putative RTKs indicate that this class of proteins also plays an important role in decisions about cell fate that depend on cellular interactions during development. The sevenless RTK mediates the position-dependent specification of a particular photoreceptor cell type (R7) in the eye. The local specification of R7 cells requires a functional tyrosine kinase domain of the sevenless protein but does not depend on the spatially restricted expression of the sevenless gene. The Drosophila EGF receptor homologue serves multiple functions during development, some of which are clearly unrelated to regulation of cell growth. Finally, the torso gene encodes an RTK required for the specification of the terminal regions of the Drosophila larva. A number of other genes have been genetically identified that appear to function in the same developmental processes upstream or downstream of these three RTKs. These loci are excellent candidates for genes encoding other components of the signalling pathways, such as ligands or substrates of the RTKs.

In vertebrates, receptor tyrosine kinases (RTKs) have been identified as growth factor receptors and proto-oncogenes. Many of these RTKs appear to play a key role in the regulation of cell growth. Recent analyses of several Drosophila genes encoding putative RTKs indicate that this class of proteins also serves an important role in cell fate decisions which depend on cellular interactions during development. The sevenless RTK mediates the position-dependent specification of a particular photoreceptor cell type (R7) in the eye. The local specification of R7 cells requires a functional tyrosine kinase domain of the sevenless protein but does not depend on the spatially restricted expression of the sevenless gene. The Drosophila EGF receptor homolog serves multiple functions during development, some of which are clearly unrelated to regulation of cell growth. Finally, the torso gene encodes an RTK required for the specification of the terminal regions of the Drosophila larva. A number of other genes have been genetically identified that appear to function in the same developmental processes upstream or downstream of these three RTKs. These loci are excellent candidates for genes encoding other components of the signalling pathways such as ligands or substrates of the RTKs.

The determination of cell fates during the assembly of the ommatidia in the compound eye of Drosophila appears to be controlled by cell-cell interactions. In this process, the sevenless gene is essential for the development of a single type of photoreceptor cell. In the absence of proper sevenless function the cells that would normally become the R7 photoreceptors instead become nonneuronal cells. Previous morphological and genetic analysis has indicated that the product of the sevenless gene is involved in reading or interpreting the positional information that specifies this particular developmental pathway. The sevenless gene has now been isolated and characterized. The data indicate that sevenless encodes a transmembrane protein with a tyrosine kinase domain. This structural similarity between sevenless and certain hormone receptors suggests that similar mechanisms are involved in developmental decisions based on cell-cell interaction and physiological or developmental changes induced by diffusible factors.

The sevenless gene controls the fate of a single photoreceptor cell type in the developing eye of Drosophila. Its RNA and protein accumulate transiently in a subpopulation of cells in the developing eye imaginal disc. We have used P-element transformation with different minigenes and marker gene constructs to identify cis-acting regulatory regions required for the complex sevenless expression pattern. Our results indicate that the upstream region of the sevenless gene is devoid of any detectable regulatory elements and that sequences located 3' to the transcription start site are sufficient to promote the sevenless expression pattern. These gene-internal sequences function in both orientations on heterologous promoters, also when placed at the 3' end of a lacZ reporter gene.

Sleep behavior between 1/2 and 5 years in 320 Swiss children of the first Zurich longitudinal study is reported. The average length of night sleep between 1/2 and 5 years was 11 to 12 hours. Day sleep was noted in 96% of the children between 6 and 24 months, and in 20% at age 5. The total length of sleep between 6 and 18 months was 15 hours per 24 hours. It diminished to 12 hours at age 5. There was a large individual variability of day sleep and of night sleep at all ages. Positive correlations were found between the lengths of day sleep at different ages and between the lengths of night sleep at different ages. The length of day sleep and that of night sleep was negatively correlated between 2 and 5 years. Evening wakefulness was observed in 16% and night waking in 40 to 50% of all children. 18% woke up at least once each night. Night wakening between 2 and 5 years was positively correlated. In about half of the children with evening wakefulness and/or night wakening these sleep behaviors were considered as abnormal by the mothers.

The sevenless (sev) gene determines the fate of a single photoreceptor cell type in the eye of Drosophila. It encodes a putative cell-surface protein with homology to tyrosine kinases. Here we have determined the complete structure of the sev gene and have demonstrated that the role of the sev protein in this developmental decision is critically dependent on the tyrosine kinase function. In comparison with other known tyrosine kinases, the sev gene product is unique in size and structure. It is a polypeptide of 2554 amino acids with two putative transmembrane segments. A single amino acid substitution in the ATP-binding site of the putative kinase domain results in the synthesis of an inactive sev protein unable to determine cell fate.

PrP 27-30 is the major protein in purified preparations of scrapie agent. An almost complete PrP cDNA was used to select PrP-related genomic clones from normal hamster DNA. The gene contains a noncoding exon of 56 to 82 bp and a 2 kb coding exon, separated by a 10 kb intron. Transcription initiates at the same multiple sites in vivo and in vitro. The promoter lacks a TATA box and contains three repeats of the sequence GCCCCGCCC, which resembles the Sp1 binding site found in "housekeeping" genes. The PrP coding sequence encodes a presumptive amino-terminal signal peptide. The primary structure of PrP encoded by the gene of a healthy animal does not differ from that encoded by a cDNA from a scrapie-infected animal, suggesting that the different properties of PrP from normal and scrapie-infected brains are due to post-translational events.

Specification of cell fate in the compound eye of Drosophila appears to be controlled entirely by cell interactions. The sevenless gene is required for the correct determination of one of the eight photoreceptor cells (R7) in each ommatidium. It encodes a transmembrane protein with a tyrosine kinase domain and is expressed transiently on a subpopulation of ommatidial precursor cells including the R7 precursors. It is shown here that heat shock-induced indiscriminate expression of a sevenless complementary DNA throughout development can correctly specify R7 cell identity without affecting the development of other cells. Furthermore, discontinuous supply of sevenless protein during eye development leads to the formation of mosaic eyes containing stripes of sevenless+ and sevenless- ommatidia, suggesting that R7 cell fate can be specified only within a relatively short period during ommatidial assembly. These results support the hypothesis that the specification of cell fate by position depends on the interaction of a localized signal with a receptor present on many undifferentiated cells, and that the mere presence of the receptor alone is not sufficient to specify cell fate.

The development of the compound eye of Drosophila consists of a linear, stereotyped program starting at the posterior end of the eye imaginal disc and progressing towards the anterior border. The determination of the R7 photoreceptor cells is part of this process and is dependent on the sevenless gene. In this study, we used a heat-shock-inducible sevenless gene as a conditional allele to determine the exact temporal requirements of sevenless gene expression and to reveal the stages of ommatidial development during which the presumptive R7 cell can respond to the presence of sevenless protein. Our results indicate that sevenless gene function is only required during a brief, defined period for the initiation of R7 development; subsequently sevenless is dispensable for both differentiation and function of the R7 photoreceptors. Furthermore, using rescue of R7 cells as an internal marker to monitor the progression of eye development we could examine when and at what rate ommatidial columns form.