Search PubMed⌕ Search

Biomedical subjects

L Y Jan

Publications and source records attributed to L Y Jan.

At least 109 records · Page 6Linked to original sources
PubMed1996

Asymmetric localization of a mammalian numb homolog during mouse cortical neurogenesis.

During Drosophila neurogenesis, differential segregation of Numb is necessary for daughter cells of asymmetric divisions to adopt distinct fates, at least partly by biasing the Notch-mediated cell-cell interaction. We have isolated a highly conserved mammalian homolog of Drosophila numb, m-numb. During mouse cortical neurogenesis, m-Numb is asymmetrically localized to the apical membrane of dividing ventricular neural progenitors. Depending upon the orientation of the cleavage plane, m-Numb may be distributed into one or both of the daughter cells. When expressed in Drosophila embryos, m-Numb is localized asymmetrically in dividing neural precursors and rescues the numb mutant phenotype. Furthermore, m-Numb can physically interact with mouse Notch1. We propose that some shared molecular mechanisms, both cell-intrinsic and cell-extrinsic, generate asymmetric cell divisions during neurogenesis of vertebrates and invertebrates.

Amino Acid Sequence↗
PubMed1996

A strongly inwardly rectifying K+ channel that is sensitive to ATP.

We have cloned an inwardly rectifying K+ channel from the hamster insulinoma cDNA library and shown that it is inhibited by cytoplasmic ATP. The channel is 90.97% identical to the IRK3 channels cloned from other species, and its mRNA is found primarily in the brain. When expressed in Xenopus oocytes, the channel displays strong inward rectification typical of inward rectifiers. The channel is inhibited reversibly by physiological concentrations of ATP via a mechanism that does not appear to involve ATP hydrolysis, as shown by studies of channels in excised inside-out membrane patches. This effect is antagonized by ADP, again in the physiological range, implying that this channel is sensitive to the index of metabolic state, i.e., the intracellular [ATP]/[ADP] ratio. This channel is different from previously known ATP-sensitive K+ channels, although it may also be stimulated by MgATP, as are other ATP-sensitive K+ channels. The potential physiological significance of these ATP-dependent regulations will be discussed.

Adenosine Diphosphate↗
PubMed1995

dpa, a member of the MCM family, is required for mitotic DNA replication but not endoreplication in Drosophila.

We have isolated the Drosophila disc proliferation abnormal (dpa) gene, a member of the MCM family of DNA replication factors. Members of this family of proteins are required for DNA replication in yeast. A dpa null mutant dies during pupal stages because imaginal tissues necessary for the formation of the adult fly fail to proliferate normally. Beginning in late embryogenesis BrdU labeling reveals DNA replication defects in mitotically proliferating cells. In contrast, dpa is dispensable for endoreplication, a specialized cell cycle consisting of consecutive rounds of S phases without intervening mitosis. Our studies suggest an essential role for dpa in mitotic DNA replication but not in endoreplication. Thus, dpa is not a general replication factor but may play a specialized regulatory role in DNA replication.

Amino Acid Sequence↗
PubMed1995

Assembly of voltage-gated potassium channels. Conserved hydrophilic motifs determine subfamily-specific interactions between the alpha-subunits.

Voltage-gated potassium (K+) channels are assembled by four identical or homologous alpha-subunits to form a tetrameric complex with a central conduction pore for potassium ions. Most of the cloned genes for the alpha-subunits are classified into four subfamilies: Kv1 (Shaker), Kv2 (Shab), Kv3 (Shaw), and Kv4 (Shal). Subfamily-specific assembly of heteromeric K+ channel complexes has been observed in vitro and in vivo, which contributes to the diversity of K+ currents. However, the molecular codes that mediate the subfamily-specific association remain unknown. To understand the molecular basis of the subfamily-specific assembly, we tested the protein-protein interactions of different regions of alpha-subunits. We report here that the cytoplasmic NH2-terminal domains of Kv1, Kv2, Kv3, and Kv4 subfamilies each associate to form homomultimers. Using the yeast two-hybrid system and eight K+ channel genes, two genes (one isolated from rat and one from Drosophila) from each subfamily, we demonstrated that the associations to form heteromultimers by the NH2-terminal domains are strictly subfamily-specific. These subfamily-specific associations suggest a molecular basis for the selective formation of heteromultimeric channels in vivo.

Amino Acid Sequence↗
PubMed1995

Asymmetric segregation of Numb and Prospero during cell division.

A cell can divide asymmetrically by specifically segregating a determinant into one of its daughter cells. The Numb protein is a candidate for such a determinant in the asymmetric cell divisions of the developing Drosophila nervous system. Numb is a membrane-associated protein that localizes asymmetrically during cell division and segregates into one daughter cell, where it is required for the specification of the correct cell fate. Here we show that a nuclear protein, Prospero, translocates to the membrane at the beginning of cell division and colocalizes with Numb throughout mitosis, suggesting a common mechanism for asymmetric segregation. Numb and Prospero localization is coupled to mitosis and tightly correlated with the position of one of the two centrosomes. In contrast to centrosome positioning, however, Numb and Prospero localization is independent of microtubules. Cytochalasin D treatment suggests that the process is also independent of actin. We propose that there is an organizer of asymmetric cell division which provides positional information for both the orientation of the mitotic spindle and asymmetric localization of Numb and Prospero.

Actins↗
PubMed1995

Cloning of rat KATP-2 channel and decreased expression in pancreatic islets of male Zucker diabetic fatty rats.

ATP-regulated potassium channels play a key role in regulating insulin secretion. We have isolated cDNA clones from a RINm5F insulinoma cell cDNA library that encode a protein, KATP-2, whose sequence shows 72% identity with the rat heart potassium channel KATP. RNA blotting showed that KATP-2 mRNA was present at high levels in brain and undetectable in heart, spleen, lung, liver, skeletal muscle, kidney and testis. A quantitative RT-PCR assay indicated that there were 1.85 +/- 0.32 x 10(5) molecules of KATP-2 mRNA per microgram of total RNA in pancreatic islets from nondiabetic rats. The levels of KATP-2 mRNA were reduced by 34% in islets from diabetic Zucker diabetic fatty male rats, a model of non-insulin dependent diabetes mellitus, compared to their lean nondiabetic littermates (p < 0.05), suggesting that decreased expression of KATP-2 may contribute to beta-cell dysfunction in this animal model.

Adenosine Triphosphate↗
PubMed1995

Determination of the subunit stoichiometry of an inwardly rectifying potassium channel.

Inwardly rectifying K+ channels are distantly related to their voltage-gated counterparts and possess a structural motif of only two putative transmembrane segments in each subunit. They are formed by the assembly of an unknown number of subunits. We have examined the subunit stoichiometry of a strongly rectifying K+ channel, IRK1, by linking together the coding sequence of three or four subunits and distinguishing channels with different numbers of subunits carrying a double mutation that alters inward rectification and single-channel properties. We find that IRK1 channels, like voltage-gated K+ channels, are tetrameric channels. Interestingly, the high sensitivity to Mg2+ and polyamines, cations that produce inward rectification by blocking the channel pore from the cytoplasmic side is largely retained in a channel containing only one wild-type subunit and three subunits bearing mutations that abolish high affinity Mg2+ and polyamine block.

Animals↗
PubMed1995

Mutations that affect the length, fasciculation, or ventral orientation of specific sensory axons in the Drosophila embryo.

In wild-type Drosophila embryos, five lateral chordotonal (lch) axons in each abdominal hemisegment originate from a midlaterally positioned cluster of neurons and grow, fasciculate, and orient ventrally as they connect with targets in the CNS. We have identified 22 recessive lethal mutations in 12 complementation groups, 8 of which are novel, that differentially affect lch axon growth, fasciculation, or ventral orientation. Mutations in 3 loci result in shorter, but fasciculated and ventrally directed axon bundles. Mutations in 4 complementation groups cause lch axon defasciculation. Mutations in 7 complementation groups cause some lch axon bundles to grow dorsally along a trajectory 180 degrees from normal.

Animals↗
PubMed1995

Evidence that direct binding of G beta gamma to the GIRK1 G protein-gated inwardly rectifying K+ channel is important for channel activation.

Activation of G protein-gated K+ channels by G protein-coupled receptors contributes to parasympathetic regulation of heart rate in the atrium and inhibitory postsynaptic potentials in the peripheral and central nervous system. Having found that G beta gamma activates the cloned GIRK1 channel, we now report evidence for direct binding of G beta gamma to both the N-terminal hydrophilic domain and amino acids 273-462 of the C-terminal domain of GIRK1. These direct interactions are physiologically important because synthetic peptides derived from either domain reduce the G beta gamma binding as well as the G beta gamma activation of the channel. Moreover, the N-terminal domain may also bind trimeric G alpha beta gamma, raising the possibility that physical association of G protein-coupled receptors, G proteins, and K+ channels partially accounts for their compartmentalization and hence rapid and specific channel activation by receptors.

Amino Acid Sequence↗
PubMed1995

Identification of structural elements involved in G protein gating of the GIRK1 potassium channel.

Chimeras of GIRK1 and IRK1, a G protein-insensitive inward rectifier, are activated by coexpression of G beta gamma if they contain either the N-terminal or part of the C-terminal hydrophilic domain of GIRK1. The N-terminal domain of GIRK1 also facilitates the fast rates of activation and deactivation following m2 muscarinic receptor stimulation. The hydrophobic core of GIRK1 (M1-H5-M2) is important for determining the brief single-channel open times typical of GIRK1 but not important for determining G beta gamma sensitivity. Coexpression with CIR revealed that the gating properties associated with different GIRK1 domains could not have arisen from altered ability to form heteromultimers. These results implicate specific regions of GIRK1 in G protein activation and suggest that GIRK1 may be closely linked to the m2 muscarinic receptor-G protein complex.

Animals↗
PubMed1995

tramtrack acts downstream of numb to specify distinct daughter cell fates during asymmetric cell divisions in the Drosophila PNS.

Asymmetric cell divisions allow a sensory organ precursor (SOP) cell to generate a neuron and its support cells in the Drosophila PNS. We demonstrate a role of tramtrack (ttk), previously identified as a zinc finger-containing putative transcription factor, in the determination of different daughter cell fates. Both loss of function and overexpression of ttk affect the fates of the SOP progeny. Whereas loss of ttk function transforms support cells to neurons, ttk overexpression results in the reverse transformation. ttk is expressed in support cells but not in neurons. It has been shown that numb, a membrane-associated protein asymmetrically distributed during the SOP division, confers different daughter cell fates. Loss of ttk or numb function results in reciprocal cell fate transformation. Epistatic studies suggest that ttk acts downstream of numb. We propose that ttk executes the command dictated by asymmetrically localized numb to specify distinct daughter cell fates during multiple asymmetric divisions.

Animals↗
PubMed1995

Control of rectification and permeation by residues in two distinct domains in an inward rectifier K+ channel.

Inwardly rectifying K+ channels conduct more inward than outward current as a result of voltage-dependent block of the channel pore by intracellular Mg2+ and polyamines. We investigated the molecular mechanism and structural determinants of inward rectification and ion permeation in a strongly rectifying channel, IRK1. Block by Mg2+ and polyamines is found not to conform to one-to-one binding, suggesting that a channel pore can accommodate more than one blocking particle. A negatively charged amino acid in the hydrophilic C-terminal domain is found to be critical for both inward rectification and ion permeation. This residue and a negatively charged residue in the putative second transmembrane segment (M2) contribute independently to high affinity binding of Mg2+ and polyamines. Mutation of this residue also induces Mg(2+)- and polyamine-independent inward rectification and dramatically alters single-channel behavior. We propose that the hydrophilic C-terminal domain comprises part of the channel pore and that involvement of both hydrophilic and hydrophobic domains in pore lining may provide a molecular basis for the multi-ion, long-pore nature of inwardly rectifying K+ channels.

Amino Acids↗
PubMed1995

Role of the proneural gene, atonal, in formation of Drosophila chordotonal organs and photoreceptors.

The Drosophila gene atonal encodes a basic helix-loop-helix protein similar to those encoded by the proneural genes of the achaete-scute complex (AS-C). The AS-C are required in the Drosophila PNS for the selection of neural precursors of external sense organs. We have isolated mutants of atonal, which reveal that this gene encodes the proneural gene for chordotonal organs and photoreceptors. In atonal mutants, all observable adult chordotonal organs, and almost all embryonic chordotonal organs fail to form; all adult photoreceptors are missing. For both types of sense organ, this defect is already apparent at the level of precursor formation. Therefore it is a failure in the epidermal-neural decision process i.e. a proneural defect. The failure to form photoreceptors results in atrophy of the atonal mutant imaginal disc, due to apoptosis and lack of stimulation of division. Lack of photoreceptors should also eliminate signalling that arises from differentiating photoreceptors and is required for morphogenetic furrow movement in the wild-type eye disc. Nevertheless, a remnant morphogenetic furrow is still observed in the atonal mutant disc. This presumably reflects the process of furrow initiation, which would not depend on signals from developing photoreceptors.

Animals↗
PubMed1995

The Shaker-like potassium channels of the mouse rod bipolar cell and their contributions to the membrane current.

RT PCR on mRNA from enzymatically dissociated, isolated bipolar cells showed that these neurons express the Shaker-like K+ channels Kv1.1, Kv1.2, and Kv1.3. Immunohistochemical localization showed each channel to have a unique subcellular distribution: Kv1.1 immunoreactivity was detected in the dendrites and axons terminal, whereas Kv1.2 and Kv1.3 subunits were localized to the axon and the postsynaptic membrane of the rod ribbon synapse, respectively. Whole-cell patch-clamp recordings indicated that the activation voltage of the delayed rectifier current of the isolated bipolar cell and the inhibitory constants for current blockade by TEA, 4-AP, and Ba2+ were similar to these same properties measured for Kv1.1 expressed in oocytes. However, the TEA and 4-AP inhibitory constants for the bipolar cell current differed from the inhibitory constants for Kv1.2 or Kv1.3. These results suggest that the current of the isolated rod bipolar cell is most similar to Kv1.1 but that all three channels may function in the intact retina to allow complex modulation of retinal synaptic signals.

Animals↗
PubMed1994

Germ cell-less encodes a cell type-specific nuclear pore-associated protein and functions early in the germ-cell specification pathway of Drosophila.

The maternally supplied plasm at the posterior pole of a Drosophila embryo contains determinants that specify both the germ-cell precursors (pole cells) and the posterior axis. One pole plasma component, the product of the germ cell-less gene, has been found to be required for specification of pole cells, but not posterior somatic cells. Mothers with reduced levels of gcl give rise to progeny that lack pole cells, but are otherwise normal. Mothers overexpressing gcl, on the other hand, produce progeny exhibiting a transient increase of pole cells. Ectopic localization of gcl to the anterior pole of the embryo causes nuclei at that location to adopt characteristics of pole cell nuclei, with concurrent loss of somatic cells. We also present evidence indicating that the gcl protein associates specifically with the nuclear pores of the pole cell nuclei. This localization suggests a novel mechanism in the specification of cell fate for the germ line.

Animals↗
PubMed1994

Potassium channels and their evolving gates.

Potassium channels allow potassium ions to flow across the membrane and play a key role in maintaining membrane potential. Recent research has begun to reveal how these channels transport potassium in preference to other ions, how their activity is controlled, and how they are related to other channels.

Amino Acid Sequence↗