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L Y Jan

Publications and source records attributed to L Y Jan.

At least 181 records · Page 10Linked to original sources
PubMed1991

Neuroectoderm in Drosophila embryos is dependent on the mesoderm for positioning but not for formation.

By studying neuroectoderm formation in the absence of mesoderm and mesectoderm in mutants of the zygotic genes snail and twist, we have found that the number of neuroblasts is not reduced in these mutants, suggesting that mesoderm and mesectoderm are not essential for the initiation of neural development. The position of the neuroectoderm, however, is ventrally shifted: Neuroectoderm takes over the presumptive peripheral mesoderm domain in single mutants, whereas the entire presumptive mesoderm domain in double mutants takes on the neuroectodermal fate. The shifted neuroectoderm still requires the proneural genes and the neurogenic genes. This shift is unlikely to be due to any shift in the nuclear localization gradient of the maternally supplied dorsal protein. A model for cell fate determination of the neuroectoderm, mesectoderm, and mesoderm will be discussed.

Animals↗
PubMed1990

Evidence for the formation of heteromultimeric potassium channels in Xenopus oocytes.

Potassium channels show a wide range of functional diversity. Nerve cells typically express a number of K+ channels that differ in their kinetics, single-channel conductance, pharmacology, and sensitivity to voltage and second messengers. The cloning of the Shaker gene in Drosophila, and of related genes, has revealed that the encoded K+ channel polypeptides resemble one of the four internally homologous domains of the alpha-subunits of Na+ channels and Ca2+ channels, indicating that K+ channels may form by the co-assembly of several polypeptides. In this report we provide evidence that the Shaker A-type K+ channels expressed in Xenopus oocytes contain several Shaker polypeptides, that heteromultimeric channels may form through assembly of different channel polypeptides, that the kinetics or pharmacology of some heteromultimeric channels differ from those of homomultimeric channels, and that channel polypeptides from the fruit fly can co-assemble with homologous polypeptides from the rat. We suggest that heteromultimer formation may increase K+ channel diversity beyond even the level expected from the large number of K+ channel genes and alternative splicing products.

Animals↗
PubMed1990

Similarity of the product of the Drosophila neurogenic gene big brain to transmembrane channel proteins.

Cells in the neurogenic region of Drosophila embryos are initially bipotential; they can become either neuroblasts or epidermoblasts. Cell-cell interaction seems to play an important part in this developmental decision, which involves the function of a group of genes (the neurogenic genes). Loss-of-function mutations in any of the neurogenic genes result in nervous system hyperplasia and epidermal hypoplasia. Of the six known zygotic neurogenic genes, big brain (bib) is unique in several aspects. Most notably, all the other known neurogenic genes seem to fit into a cascade defined by genetic interactions, whereas bib does not show any detectable interaction with them. To understand how bib functions, we have now cloned the bib genomic and complementary DNAs. The predicted bib product shows significant sequence similarity to a family of transmembrane proteins, some of which form channels permeable to small molecules. Together with genetic studies, our results indicate that the bib product may mediate intercellular communication in a pathway separate from the one involving the products of the other neurogenic genes.

Amino Acid Sequence↗
PubMed1990

Genes required for specifying cell fates in Drosophila embryonic sensory nervous system.

The nervous system contains a diverse group of cells. Specification of the correct cell fate is obviously important for the proper function of the nervous system, yet how are the fates of different neurons determined during development? Very little is known about the underlying molecular mechanisms used in the mammalian nervous system. How, for example, are certain cells directed to form pyramidal cells rather than local interneurons? In the fruit fly Drosophila melanogaster, and the nematode Caenorhabditis elegans, some progress has been made in studying neuronal fate determination. For instance, in Drosophila, a number of genes acting at different levels have been found to control this process. They function to (1) endow a subset of the ectodermal cells in the early embryo with the potential to become neuronal precursors, (2) commit some of these cells to the fate of neuronal precursors, (3) specify the identity of these neuronal precursors, and (4) specify the identity of the individual progeny cells of a neuronal precursor. In this review, we discuss first the rationale of the genetic approach, then outline the working hypothesis and, finally, briefly describe the genes known to be involved in the formation of the sensory nervous system in Drosophila. We also discuss the prospects for extrapolating these molecular mechanisms and principles to vertebrate and invertebrate neural development.

Animals↗
PubMed1990

How might the diversity of potassium channels be generated?

Potassium channels are a diverse group of ion channels present in most eukaryotic cells that have been examined. Over 30 different potassium channels have been characterized biophysically. They show different sensitivities to voltage and/or intracellular messengers, and have different kinetic or pharmacological properties. The wide range of potassium channel properties reflects the broad spectrum of cellular functions that they serve, including control of synaptic efficacy, of heart beat, and of endocrine and exocrine secretion. How might this tremendous diversity of potassium channels be generated? Partial answers have begun to emerge as molecular studies of potassium channel genes have become possible over the past few years.

Animals↗
PubMed1990

Functional expression of Shaker K+ channels in a baculovirus-infected insect cell line.

We constructed a recombinant baculovirus, A. californica nuclear polyhedrosis virus, containing the Drosophila Shaker H4 K+ channel cDNA under control of the polyhedrin promoter. When infected with this recombinant baculovirus, the cell line Sf9, derived from the army-worm caterpillar S. frugiperda, expresses fully functional Shaker transient K+ currents, as assayed by whole-cell recording. K+ currents begin to appear at about 15 hr after infection, and they continue to increase over the next 3 days. Over the same period of time, a 75 kd band appears on SDS gels stained with Coomassie blue. The identity of this band as a Shaker gene product is confirmed by Western blot analysis using an anti-Shaker antiserum. The 75 kd band accounts for a substantial fraction of the membrane protein in Shaker-infected Sf9 cells. These results give hope that the baculovirus system, which has been used successfully for high-level expression of soluble proteins from higher eukaryotes, may be appropriate for producing large amounts of cloned ion channel proteins as well.

Animals↗
PubMed1990

Immunological characterization of K+ channel components from the Shaker locus and differential distribution of splicing variants in Drosophila.

Antibodies were raised to three portions of the predicted sequences of Shaker, a gene that encodes a family of K+ channel components that are produced by the alternative splicing of transcripts. On immunoblots, the protein products appear to be 65,000-85,000 daltons in size. No smaller products were detected. Immunocytochemistry has revealed a nonuniform distribution of Shaker products in the brain of the adult fly. By comparing antisera directed against regions shared by all the splicing variants to antisera that are directed against one particular group of splicing variants, we have determined that there is a differential distribution of that group of variants. Thus, the alternative splicing of Shaker transcripts appears to produce different subtypes of A-channels in different tissues.

Amino Acid Sequence↗
PubMed1990

rhomboid, a gene required for dorsoventral axis establishment and peripheral nervous system development in Drosophila melanogaster.

rhomboid (rho) belongs to a group of four genes involved in the elaboration of positional information at a ventrolateral level in the Drosophila embryo. Mutations at any of these four loci also lead to a variety of other phenotypes, including reduction in the number of stretch receptor organs (chordotonal organs) in the peripheral nervous system (PNS). We have cloned rho with the aid of a lacZ-bearing P-element inserted into the rho gene. In the early blastoderm stage, a putative rho transcript is expressed in ventrolateral strips corresponding to the domain of activity of the rho gene on the embryonic fate map. Later expression of the transcript correlates with regions of the embryo that are disrupted in rho mutants and includes a cell that may be the precursor for the missing stretch receptor organs. We hypothesize that rho acts very early in differentiation pathways to specify the identities of domains and isolated precursor cells. Sequence analysis suggests that this transcript codes for a trans-membrane protein.

Amino Acid Sequence↗
PubMed1990

Patterns of expression of cut, a protein required for external sensory organ development in wild-type and cut mutant Drosophila embryos.

The loss of cut activity in Drosophila results in the transformation of the neurons and support cells of external sensory (es) organs into those of chordotonal (ch) organs. The cut locus encodes a homeo domain-containing protein, which is expressed in the cells of es, but not in ch, organs. We show by Western analyses the presence of two embryonic protein species whose approximate relative molecular masses of 280 and 320 kD are compatible with that predicted from the primary sequence. We also describe the development of the Cut protein expression pattern and show that Cut is expressed in sensory precursor cells that divide to give rise to es organs. Finally, we analyze the changes in the Cut expression pattern of several mutant alleles of the complex cut locus and show that the mutations affecting es organ development are associated with either altered protein distribution in the PNS or incorrect subcellular Cut protein localization.

Animals↗
PubMed1990

Molecular studies of voltage-gated potassium channels.

The cloning and characterization of the voltage-activated Shaker potassium channel gene in Drosophila have led to the identification of structural elements involved in potassium channel gating. As found for the voltage-activated sodium channel, the S4 segment, located in the conserved core of the protein, plays a central role in voltage-dependent activation. Potassium channels appear to be formed by the assembly of several polypeptides into multisubunit channels. This is directly analogous to the proposed folding of the four internally homologous pseudosubunits of sodium and calcium channels. The amino- and carboxy-terminal regions of Shaker channels are specialized for, and appear to interact in, inactivation gating. This interaction probably includes interaction between subunits, as may be said for the role in inactivation gating of the junction between the carboxyl terminus of the third domain and amino terminus of the fourth domain of sodium channel (Vassilev et al. 1988). The capacity for coassembly in potassium channels extends not only to the alternatively spliced products of the same gene, but also to the products of different genes. Heteromultimeric channels that are formed in this way have kinetic and pharmacological properties that differ from homomultimers of their constituents and, as such, broaden the functional diversity of channels that can be produced by any given number of compatible potassium channel genes.

Animals↗
PubMed1990

Localization of vasa, a component of Drosophila polar granules, in maternal-effect mutants that alter embryonic anteroposterior polarity.

Cytoplasm at the posterior pole of the early Drosophila embryo, known as polar plasm, serves as a source of information necessary for germ cell determination and for specification of the abdominal region. Likely candidates for cytoplasmic elements important in one or both of these processes are polar granules, organelles concentrated in the cortical cytoplasm of the posterior pole. Females homozygous for any one of the maternal-effect mutations, tudor, oskar, staufen, vasa, or valois give rise to embryos that lack localized polar granules, fail to form the germ cell lineage and have abdominal segment deletions. Using antibodies against a polar granule component, the vasa protein, we find that vasa synthesis or localization is affected by these mutations. In vasa mutants, synthesis of vasa protein is absent or severely restricted. In oskar and staufen mutant females, vasa synthesis appears normal, but the vasa protein is not localized. In tudor and valois mutant females, vasa is localized to the posterior pole of oocytes, but this localization is lost following egg activation. In addition to the posterior localized vasa, there is a low level of vasa distributed throughout the embryo. A function for this distributed vasa is postulated based on the observation that embryos from Bicaudal-D mothers, in which abdominal determinants are incorrectly localized to the anterior pole, do not show any ectopic vasa localization, though abdomen development at the anterior end depends on the amount of vasa protein in the embryo.

Animals↗
PubMed1990

A new homeobox-containing gene, msh-2, is transiently expressed early during mesoderm formation of Drosophila.

Many homeobox-containing genes of Drosophila regulate pathways of differentiation. These proteins probably function as promoter- or enhancer-selective transcription factors. We have isolated a new homeobox-containing gene, msh-2, by means of the polymerase chain reactions (PCR) using redundant primers. msh-2 is specifically expressed in mesodermal primordia during a short time period early in development. It first appears at blastoderm stage just before the ventral invagination of the mesoderm and shortly after twist, a gene required for mesoderm formation, is expressed. During germband elongation all the mesodermal cells in the segmented part of the embryo express msh-2, but soon afterwards msh-2 becomes restricted to the dorsal mesoderm, which includes the primordia for the visceral musculature and the heart. Prior to muscle differentiation, msh-2 expression ceases, except for two rows of cells that will be included in the dorsal vessel. Embryos that are deficient for the chromosomal region, 93C-F, which includes the msh-2 gene, show normal mesoderm invagination and dorsal spreading. However, later in development no visceral muscle and dorsal vessel differentiation can be detected, but some skeletal muscles do form, albeit abnormally. msh-2 expression, except for a patch in the head, is dependent on twist function. On the other hand, snail, another mesoderm determinant, does not appear to be required for msh-2 initiation, but is necessary for the maintenance of msh-2 expression after germband elongation. H2.0, a homeo-box-containing gene specifically expressed in visceral mesoderm, is not transcribed in the mesoderm in 93C-F deficiency embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1989

Interactions between heterologous helix-loop-helix proteins generate complexes that bind specifically to a common DNA sequence.

A DNA binding and dimerization motif, with apparent amphipathic helices (the HLH motif), has recently been identified in various proteins, including two that bind to immunoglobulin enhancers (E12 and E47). We show here that various HLH proteins can bind as apparent heterodimers to a single DNA motif and also, albeit usually more weakly, as apparent homodimers. The HLH domain can mediate heterodimer formation between either daughterless, E12, or E47 (Class A) and achaete-scute T3 or MyoD (Class B) to form proteins with high affinity for the kappa E2 site in the immunoglobulin kappa chain enhancer. The achaete-scute T3 and MyoD proteins do not form kappa E2-binding heterodimers together, and no active complex with N-myc was evident. The formation of a heterodimer between the daughterless and achaete-scute T3 products may explain the similar phenotypes of mutants at these two loci and the genetic interactions between them. A role of E12 and E47 in mammalian development, analogous to that of daughterless in Drosophila, is likely.

Animals↗
PubMed1989

numb, a gene required in determination of cell fate during sensory organ formation in Drosophila embryos.

Neurons and support cells of each sensory organ in Drosophila embryos are most likely derived from a single precursor cell. This cell lineage is affected in numb mutants. Morphological alterations of sensory structures, as well as changes in the number of cells expressing cell type-specific markers, indicate that sensory neurons in numb mutant embryos are transformed into lineage-related nonneuronal support cells. Thus the numb gene controls the fate of progeny derived from sensory organ precursors. The numb gene has been isolated by the plasmid rescue method. The structure of its predicted product is discussed.

Amino Acid Sequence↗
PubMed1988

daughterless, a Drosophila gene essential for both neurogenesis and sex determination, has sequence similarities to myc and the achaete-scute complex.

daughterless (da) has multiple functions in Drosophila embryonic development: maternal da activity is necessary for proper sex determination, and zygotic da activity is necessary for formation of the peripheral nervous system. We have cloned the region containing da and have found that five recessive lethal da mutations map to a single transcription unit. A predicted protein product of this transcription unit has sequence similarities with the oncogene myc, with the gene MyoD1, which is involved in myoblast determination, and with the Drosophila achaete-scute complex, which is involved in neuronal precursor determination. The role of da as a gene controlling cell determination in multiple developmental pathways is discussed.

Amino Acid Sequence↗