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S Lee

Publications and source records attributed to S Lee.

At least 991 records · Page 55Linked to original sources
PubMed1994

Expression of cAMP-dependent protein kinase in prespore cells is sufficient to induce spore cell differentiation in Dictyostelium.

The activity of cAMP-dependent protein kinase (PKA) is required for proper development at several stages during the Dictyostelium life cycle. We present evidence that activation of PKA is rate-limiting for the differentiation of prespore cells to spores and that PKA activation may be the developmental trigger for sporulation. Strains that overexpress the gene encoding the catalytic subunit of PKA (PKAcat) or lack a functional regulatory subunit (rdeC strains) undergo rapid, heterochronic development. We show that overexpression of PKAcat in prespore cell is sufficient to directly induce expression of the spore maturation marker spiA and differentiation to spores, in a cell-autonomous manner. Moreover, overexpression of PKAcat in prespore cells can bypass a mutation that blocks an earlier developmental step to induce spiA expression. Our results suggest that the regulatory pathway in prespore cells between the activation of PKA and spiA induction/spore maturation is quite short and that PKAcat expression in prespore cells may mediate spore differentiation at the level of transcription. This induction of sporulation requires the prior activation of the prespore cell pathway. In addition, we show that beta-galactosidase activity expressed from a PKAcat promoter/lacZ reporter construct is highly enriched in the anterior prestalk A region during the tipped aggregate, slug, and early culminant stages and that this pattern switches abruptly to a prespore pattern at the time of spore maturation, supporting the proposed role of PKA in this process.

Animals↗
PubMed1994

The G alpha subunit G alpha 4 couples to pterin receptors and identifies a signaling pathway that is essential for multicellular development in Dictyostelium.

In this paper, we show that the G alpha subunit G alpha 4 couples to pterin receptors and identifies a signalling pathway that is essential for multicellular development in Dictyostelium. G alpha 4 is developmentally regulated, is essential for proper morphogenesis and spore production, and functions cell nonautonomously. We show that G alpha 4 is coupled to receptors (alpha FAR) that activate chemotaxis and adenylyl and guanylyl cyclases in response to folate during the early stages of development and to a late class of folate receptors (beta FAR) that have different specificities for pterins. G alpha 4 is preferentially expressed in cells randomly distributed within the aggregate that are a component of the anterior-like cell population, and it is not detectably expressed in prespore cells. Our results suggest that an endogenous factor, possibly a pterin, produced during multicellular development is a requisite signal for multicellular development, acting through G alpha 4. We propose that the G alpha 4-expressing cells function as a regulatory cell type controlling prespore cell fate, possibly in response to an endogenous pterin. Our results indicate that G alpha 4 and G alpha 2 have parallel functions in mediating cellular responses to folate (pterins) and cAMP, respectively.

Adenylyl Cyclases↗
PubMed1994

Spinal motion after cervical fusion. In vivo assessment with roentgen stereophotogrammetry.

STUDY DESIGN: A roentgen stereophotogrammetric (RS) technique using metallic markers was used to determine in vivo three-dimensional (3-D) motion data in the post-operative cervical spine. Two patients were examined with RS following fusion for up to 12 months at scheduled intervals. OBJECTIVES: The study was designed to develop a technique and provide an in vivo assessment of the fusion process following surgery. Besides the researchers and surgeons, this type of information is of particular interest to the FDA and implant manufacturers. SUMMARY OF BACKGROUND DATA: The high accuracy of the roentgen stereophotogrammetric (RS) technique using metallic markers to predict displacements across body joints, including spinal joints, has been well established in the literature. Its applications in the lumbar region to assess the fusion process as a function of time following surgery have also been reported. Similar in vivo applications (and results) dealing with the cervical region are lacking. METHODS: A roentgen stereophotogrammetric (RS) technique using metallic markers was developed. Appropriate in vitro studies were undertaken to assess its accuracy for in vivo applications in the cervical spine region. Following this, three Vitallium beads were surgically implanted in anatomically appropriate positions in of each the exposed vertebrae of two patients at the time of surgery. The patients were followed with RS serially for 12 months after surgery at scheduled intervals. At each RS session, roentgen stereo pairs of the cervical spine in neutral, maximum voluntary flexion, and maximum voluntary extension were obtained using a biplanar radiographic system. The metallic beads on the radiographs were digitized using an in-house software package to determine vertebral motions across the fused segments. RESULTS: In patient 1 (atlantoaxial fusion), the flexion-extension range of rotational motion decreased with time while the corresponding AP translation at the fusion level increased from 6 mm at 3 months post-op to 13 mm at 6 and 12 months postoperatively. The abnormal AP translation at 6 months and beyond was evident on extension/extension lateral radiographs, but the AP translation at 3 months was not visually evident. In patient 2 (anterior discectomy and interbody fusion), motions of small magnitude were observed at the fused level in all three axes. These motions actually increased over the one year observation period, but were never large enough to be visually detectable on lateral extension/extension radiographs. Patient 2 had a good clinical result despite these small motions. CONCLUSIONS: Roentgen stereophotogrammetry may detect motion in the in vivo cervical spine with a sensitivity heretofore unavailable. In patient 1, we were able to detect motion before it was visually manifest. In patient 2, small motions were detected at the level of a successful anterior cervical fusion, the significance of which remain uncertain.

Atlanto-Axial Joint↗
PubMed1994

Cloning of human and mouse brain cDNAs coding for S1, the second member of the mammalian elongation factor-1 alpha gene family: analysis of a possible evolutionary pathway.

We previously reported the cloning of a rat S1 cDNA whose deduced amino acid sequence shares high similarity (92%) with that of mammalian elongation factor-1 alpha (EF-1 alpha), a protein involved in the binding of aminoacyl-tRNA to the ribosome during peptide synthesis. We report here the isolation of a full-length cDNA from a mouse brain library and a partial-length cDNA from a human hippocampus library which share extensive sequence similarity to rat S1 cDNA. We show that, as with mammalian EF-1 alpha S, the predicted primary amino acid sequences of rat, mouse, and human S1 are almost identical, except for one conservative substitution. These results indicate that mouse and man contain a second member of the EF-1 alpha gene family, the S1 gene. They also suggest that our result obtained in rat may be extrapolated to mouse and man.

Amino Acid Sequence↗
PubMed1994

Isolation of three classes of conditional lethal Chinese hamster ovary cell mutants with temperature-dependent defects in low density lipoprotein receptor stability and intracellular membrane transport.

Fluorescence-activated cell sorting was used to isolate 19 independent, temperature-sensitive, low density lipoprotein (LDL) receptor-deficient Chinese hamster ovary cell mutants that define three recessive complementation groups, ldlE, ldlF, ldlG. LDL receptor activity, essentially normal at the permissive temperature (34 degrees C), was virtually abolished in the mutants after incubation for 8-12 h at the nonpermissive temperature (39-40.5 degrees C). The mutants died after incubation for > 24 h at 39.5 degrees C. These mutants exhibited two striking and unexpected abnormalities that suggest that they define three genes important for general vesicular membrane traffic. First, LDL receptors were degraded abnormally rapidly at the nonpermissive temperature (chloroquine inhibited this degradation in ldlE and ldlG, but not in ldlF). In ldlE cells, the rapid degradation did not require efficient receptor clustering into coated pits and was not observed for all cell surface proteins. This selective degradation may be due to endocytic missorting. Second, the mutants exhibited temperature-sensitive defects in the posttranslational processing and intracellular transport of many membrane-associated and secreted proteins, including the LDL, mannose 6-phosphate/insulin-like growth factor II, and scavenger receptors, the vesicular stomatitis virus G protein and decay accelerating factor. Although the initial synthesis, folding, and processing of precursor forms of these proteins in the endoplasmic reticulum were apparently normal at the nonpermissive temperature, there was either a delay or a block in oligosaccharide processing associated with endoplasmic reticulum to medial Golgi transport at the nonpermissive temperature. This was accompanied by a dramatic inhibition of total soluble protein secretion. The posttranslational processing defects, the instability of cell surface LDL receptors, and the defective protein secretion exhibited by these mutants suggest that the ldlE-G gene products regulate or participate in reactions that are vital for a variety of secretory and endocytic membrane transport processes. This suggestion is strongly supported by our recent observation that a cDNA encoding a component of the coatomer, epsilon-COP, corrects the mutant phenotypes of ldlF cells (Guo, Q., Vasile, E., and Krieger, M. (1994) J. Cell Biol. 125, 1213-1224). Thus, these mutant cells should prove useful for further genetic and biochemical analysis of the mechanisms underlying intracellular membrane traffic.

Animals↗
PubMed1994

Cloning of human type VII collagen. Complete primary sequence of the alpha 1(VII) chain and identification of intragenic polymorphisms.

Type VII collagen is the major, if not the exclusive, component of the anchoring fibrils, attachment structures at the dermal-epidermal basement membrane zone. In this study, we have isolated overlapping cDNA clones which correspond to full-length human type VII collagen mRNA of approximately 9.2 kilobases. The full-length cDNA sequence contains an 8,833 nucleotide open reading frame encoding 2,944 amino acids. The deduced amino acid sequence revealed the presence of a central collagenous domain flanked by a large NH2-terminal non-collagenous (NC-1) domain which consists of submodules with homology to known adhesive proteins, including nine fibronectin type III-like segments (FNIII), and a smaller COOH-terminal non-collagenous (NC-2) domain. In addition, we report six intragenic polymorphisms in the type VII collagen gene (COL7A1) which can be detected by restriction enzyme digestion of polymerase chain reaction-amplified segments. The complete cDNA sequence and polymorphisms in COL7A1 will facilitate mutational analysis and prenatal diagnosis for patients with the dystrophic forms of epidermolysis bullosa, in which mutations in COL7A1 have been demonstrated.

Amino Acid Sequence↗
PubMed1994

Structural organization of the human type VII collagen gene (COL7A1), composed of more exons than any previously characterized gene.

The human type VII collagen (COL7A1) gene is the locus for mutations in at least some cases of dystrophic epidermolysis bullosa. Here we describe the entire intron/exon organization of COL7A1, which is shown to have 118 exons, more than any previously described gene. Despite this complexity, COL7A1 is compact. Consisting of 31,132 bp from transcription start site to polyadenylation site, it is only about three times the size of type VII collagen mRNA. Thus, COL7A1 introns are small. A 71-nucleotide COL7A1 intron is the smallest intron yet reported in a collagen gene, and only one COL7A1 intron is greater than 1 kb in length. All exons in the COL7A1 triple helix coding region that do not begin with sequences corresponding to imperfections of the triple helix begin with intact codons for Gly residues of Gly-X-Y repeats. This is reminiscent of the structure of fibrillar rather than other nonfibrillar collagen genes. In addition, the COL7A1 triple helix coding region contains many exons of recurring sizes (e.g., 25 exons are 36 bp, 12 exons are 45 bp, 8 exons are 63 bp), suggesting an evolutionary origin distinct from those of other nonfibrillar collagen genes. Sequences from the 5' portion of COL7A1 are presented along with the 3766-bp intergenic sequence, which separates COL7A1 from the upstream gene encoding the core I protein of the cytochrome bc1 complex. The COL7A1 promoter region is found to lack extensive homologies with promoter regions of other genes expressed primarily in skin.

Amino Acid Sequence↗
PubMed1994

Two mode ion channels induced by interaction of acidic amphipathic alpha-helical peptides with lipid bilayers.

In order to investigate the ion permeability and selectivity of ion channel formed by amphipathic alpha-helical peptides, we designed to synthesize an acidic peptide Ac(Leu-Ala-Glu-Leu)3NHCH3 (Glu-4(3)) and its channel property was compared with a basic peptides Arg-4(3) in which Glu in Glu-4(3) was replaced by Arg. Two modes of the conductance change were observed by the interaction of Glu-4(3) with planar lipid bilayers; a steady increase of the conductance with the elapse of time (mode 1) and a spike-like increase of the current (mode 2) appearing with a lag time and overlapping the model current increase. The application of negative membrane potential induced the mode 1 current and the lowering pH decreased it, suggesting that the mode 1 current is caused by slow insertion of Glu-4(3) into the lipid bilayer and then by forming certain unknown bundles like semichannels. Mode 2 was found to be consisted of channel type opened-close current with several different conductances and relatively short opening lifetimes. There was no ion selectivity in the mode 1 current, whereas the mode 2 current was cation selective. The peptide Arg-4(3) has formed a cation-selective ion channel but not shown such two mode current changes. The membrane potential formation experiment in liposomes using DiSC3(5) also showed the cation selectivity for Arg-4(3) and non-ion selectivity for Glu-4(3). The difference between Arg-4(3) and Glu-4(3) was also observed in conformational analysis by CD and in dye-release experiment from liposome. Such difference was discussed in terms of electrostatic interaction between peptides and lipid head groups.

Amino Acid Sequence↗
PubMed1994

Interactions of N-terminal fragments of groups I and II phospholipases A2 with phospholipid bilayers and their surface recognition properties.

In order to elucidate the roles of the N-terminal segments of groups I and II phospholipases A2 (PLA2s) which have been known to have alpha-helical structure and have been assumed to be involved in the water/lipid interface recognition site, the peptides corresponding to the N-terminal moieties of group I PLA2 (Naja naja atra) and group II PLA2s (Trimeresurus flavoviridis and Crotalus atrox) were synthesized and their interactions with model membranes were studied. Circular dichroism spectra showed that N-terminal peptides of both groups I and II PLA2s took alpha-helical structure in trifluoroethanol but no significant secondary structure in buffer (pH 8.0). In the presence of acidic liposomes, N-terminal fragments of group II PLA2s formed alpha-helical structure, while that of group I PLA2 remained unaffected. The hydrophobic moments showed that amphipathicities of N-terminal fragments of group II PLA2s are evidently larger than those of N-terminal fragments of group I PLA2s. The leakage of carboxyfluorescein from acidic liposomes was induced only with group II PLA2 peptides. Large blue shift and increase in intensity of tryptophan fluorescence were also observed for group II PLA2 peptides when interacting with acidic liposomes. Such difference in the modes of interactions with lipid bilayers between N-terminal peptides of groups I and II PLA2s appears to be due in large part to the difference in intrinsic alpha-helix forming properties of their amino acid sequences. It is inferred that N-terminal amphipathic alpha-helical structures of group I PLA2s are possibly formed by assistance of a neighboring chain bridged by Cys-11 and Cys-77.

Amino Acid Sequence↗