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D Larhammar

Publications and source records attributed to D Larhammar.

At least 73 records · Page 4Linked to original sources
PubMed1995

Cloning and sequence analysis of a neuropeptide Y/peptide YY receptor Y1 cDNA from Xenopus laevis.

Neuropeptide Y (NPY) and peptide YY (PYY) are structurally related peptides that share at least two distinct receptors denoted Y1 and Y2. The Y1 receptor has previously been cloned in man, rat and mouse. We describe here the cloning and sequence of a Xenopus laevis Y1 receptor that shares 81% amino acid sequence identity with the human receptor in the region spanning transmembrane (TM) regions I to VII. The extracellular amino-terminal part, TM IV and the second extracellular loop contain several replacements suggesting that these portions have no or limited direct interactions with the peptide ligands. The intracellular regions including the carboxy-terminal tail are nearly identical between Xenopus and mammals, suggesting strong structural constraints on the portions that may interact with G proteins.

Amino Acid Sequence↗
PubMed1995

Characterization of three separated exons in the HLA class II DR region of the human major histocompatibility complex.

The human major histocompatibility complex, HLA, is a highly polymorphic gene region which includes the DRA and DRB genes. The number of DRB genes differs between haplotypes. The DR4 haplotype seems to be one of the most complex with five DRB loci, DRB1, DRB4, DRB7, DRB8, and DRB9, in addition to the single DRA locus. We determined the nucleotide sequences of three separated DRB exons located between the DRB4 locus and the DRA locus in the DR4 haplotype, two DRB signal-peptide exons (S1 and S3) and one DRB first-domain exon (locus designation DRB9). Sequence comparisons suggest the following order of events for the origin of these exons: DRB9 seems to be the oldest exon and has previously been detected in multiple HLA haplotypes. DRB9 is more divergent than the three other known DRB pseudogenes, all of which have been found in apes. This suggests that DRB9 arose prior to the hominoid divergence. An L1 repeat has been inserted 3' to DRB9. Subsequently, a LTR of the ERV9 retrovirus-like family was inserted into the L1 repeat. Such LTRs have recently been observed in some of the other DRB genes. The pseudogenes DRB7 and DRB8 (containing only exons 3-6) arose after DRB9. Finally, the separated signal peptide exons S1 and S3 were formed. The molecular characterization of these separated DRB exons and insertion elements further clarifies the complex evolutionary history of the HLA-DR region. These selectively neutral exons may serve as useful markers for tracing the phylogeny of HLA haplotypes.

Base Sequence↗
PubMed1994

A quantitative test of long-range correlations and compositional fluctuations in DNA sequences.

Recent findings concerning long-range correlations and fractals in intron-containing DNA sequences of living organisms are tested qualitatively and quantitatively. Extending previous studies, we demonstrate that these findings are trivially equivalent to variations of the base-pair composition in different regions of a DNA sequence. It is shown explicitly that a well-defined scaling or fractal exponent does not exist anywhere. Comparisons of natural DNAs with computer-generated, artificial sequences are made. The present study reveals that certain natural DNA sequences (especially those with compact genomes) do have stochastic characteristics which are intrinsically different from artificial sequences. The results for 21 DNA sequences of various types from widely different taxa are reported.

Animals↗
PubMed1994

Neuropeptide role of both peptide YY and neuropeptide Y in vertebrates suggested by abundant expression of their mRNAs in a cyclostome brain.

The evolution of the neuropeptide Y (NPY) family of peptides has been unclear despite sequence information from many vertebrates. We describe here two NPY-related peptides deduced from cDNA clones of the river lamprey (Lampetra fluviatilis), a cyclostome providing one of the best models of a primitive vertebrate brain. One peptide corresponds to NPY as it has 83% identity to human NPY and its mRNA is expressed in the lateral brainstem, dorsal spinal cord and retina. The second lamprey peptide corresponds anatomically to peptide YY (PYY) as its mRNA is found in gut cells and in medial brainstem neurons. Its sequence is 60-70% identical to both PYY and NPY of mammals. These data suggest that the gene duplication leading to NPY and PYY had already occurred in the ancestral vertebrate 450 million years ago. The expression of the presumed PYY homolog in both gut and central nervous system indicates that PYY has served the dual role as a hormone and a neuropeptide from an early stage in vertebrate evolution. The similarities in the location of NPY- and PYY-expressing cells between lamprey and mammals suggest that the functions of these peptides may have been conserved.

Amino Acid Sequence↗
PubMed1994

Variations in base pair composition and associated long-range correlations in DNA sequences--computer simulation results.

Recently, the possible occurrence of long-range correlations between nucleotides in DNA sequences of living organisms has excited considerable interest. Of particular importance is the claim that only intron-containing sequences exhibit these correlations. Different investigations, however, have disproved the claimed difference between intron-containing and intron-less DNA sequences. Moreover, very recent investigations pointed out that the long-range correlations appear only if relatively large variations in nucleotide composition along the DNA sequence are present. Furthermore, some examples demonstrated that these variations may have clear biological reasons. In this paper we investigate in detail, with the aid of computer simulations, the connection between compositional heterogeneity of a DNA sequence and the appearance of long-range correlations. As an explicit example, the DNA sequence of the lambda-phage is compared with different artificial sequences of similar compositional heterogeneity. The results demonstrate that the variations of the nucleotide composition along the sequence can fully account for all properties of the claimed long-range correlations. New results of extensive computer simulations are presented which clearly demonstrate how the apparent 'fractal' (or 'long-range-correlated') character of a sequence gradually evaporates, as the frequency of the compositional variations of a simulated sequence continuously increases.

Bacteriophage lambda↗
PubMed1994

Activation of a bulbospinal opioidergic projection by pain stimuli in the awake rat.

We examined the expression of preproenkephalin mRNA in pain-modulating regions of the rat's brainstem using in situ hybridization histochemistry. We found that neurones in the Kölliker-Fuse nucleus, which receives projections from spinal nociceptive-specific cells, express enkephalin mRNA, that this expression is increased by noxious pinch applied to the skin of awake animals, and that these enkephalinergic neurones are part of a descending system that terminates in the rostroventral medulla and the spinal cord. These findings show that natural noxious stimuli activate opioidergic bulbospinal neurones that could directly modulate spinal nociceptive transmission.

Animals↗
PubMed1994

Molecular genetic aspects of tetraploidy in the common carp Cyprinus carpio.

Genome duplications are believed to have occurred on multiple occasions in vertebrate evolution. Studies of duplicate gene loci in tetraploid animals may reveal important general aspects of gene duplication, an important mode of gene evolution in metazoans. The common carp Cyprinus carpio has twice as many chromosomes as most other cyprinid fishes due to tetraploidization previously estimated to have occurred 50 Myr ago. Our sequence analyses of duplicate carp loci suggest that the tetraploidization took place less than 16 Myr ago. This is further supported by sequence comparisons with the diploid grass carp, which seems to have diverged from the common carp approximately 19 Myr ago. Duplicate loci appear to remain expressed for millions of years and may accumulate mutations leading to drastic amino acid replacements as shown here for somatotropin. Therefore, both loci should always be characterized in molecular studies of tetraploid animals such as goldfish, salmonid fishes, and Xenopus laevis. The long life of duplicate genes may explain the occurrence of numerous large multigene families in higher metazoans.

Actins↗
PubMed1994

Simplifying genetic locus assignment of HLA-DRB genes.

The DR haplotypes of the human major histocompatibility complex have been arranged in five haplotypic groups based on genomic cloning and sequence analyses. To date, the expressed DRB sequences have been assigned to four different loci: DRB1, 3, 4 and 5. DRB1 alleles are present in all haplotypes, whereas DRB3, 4 and 5 are present only in some haplotypes. Here, Göran Andersson and colleagues suggest that DRB3, 4 and 5 sequences may be treated as a single allelic series. They argue that such a model is appropriate, since DRB3, 4 and 5 sequences are inherited in an allelic fashion, have similar genomic localization, exhibit similar levels of gene expression and are, with a few rare exceptions, not present in the same haplotype.

Alleles↗
PubMed1994

Neuropeptide-Y gene expression in the goldfish brain: distribution and regulation by ovarian steroids.

Neuropeptide-Y (NPY) has been recently cloned from a goldfish cDNA library. Using a probe derived from this cDNA clone, the distribution and regulation of NPY mRNA in the goldfish brain were examined in the present study by in situ hybridization, Northern blot analysis, and ribonuclease protection assay. Frozen tissue sections from the goldfish brain and pituitary were hybridized with a digoxigenin-labeled RNA probe. Hybridization signal was detected mainly in fore-brain regions, particularly in the nucleus entopeduncularis of the ventral telencephalon, the preoptic area (POA), the olfactory bulbs, and various thalamic regions. In the midbrain, NPY mRNA was found in the optic-tectum and locus coeruleus. Northern blot hybridization of total RNA extracted from different brain areas with a 32P-labeled RNA probe detected a single mRNA species and confirmed that most NPY mRNA was present in telencephalon/POA and optic-tectum/thalamus. Our previous physiological studies showed that the ovarian steroids testosterone (T) and estradiol (E2) have potentiating effects on the actions of NPY on gonadotropin and GH release. Therefore, we also tested the possibility that T and E2 may modulate NPY gene expression. Fish were implanted ip with pellets containing T, E2, or no steroid (control) for 5 days, RNA was extracted, and NPY mRNA levels were estimated using a ribonuclease protection assay. Pretreatment with T or E2 induced a 2- to 3-fold increase in NPY mRNA levels in the telencephalon/POA, but not in the optic-tectum/thalamus. In situ hybridization using brains taken from T-implanted fish demonstrated that the site of steroid action is the POA. This report represents the first study on NPY gene expression in a nonmammalian species and demonstrates that 1) NPY mRNA is present in the neuroendocrine regulatory centers; and 2) ovarian steroids stimulate NPY gene expression in the POA.

Animals↗
PubMed1993

Expression of peptide YY and mRNA for the NPY/PYY receptor of the Y1 subtype in dorsal root ganglia during rat embryogenesis.

We have used in situ hybridization to study the distribution of mRNA for neuropeptide Y (NPY), peptide YY (PYY) and the NPY/PYY receptor of the Y1 subtype during ontogenesis in the rat and immunohistochemistry to analyse peptide immunoreactivity for NPY and PYY. We found that mRNA and immunoreactivity for NYY are transiently expressed in dorsal root ganglia (DRG) at embryonic day 16 (E16). In contrast, neither NPY mRNA nor NPY-like immunoreactivity were found in DRG at any developmental stage. The Y1 receptor mRNA is not expressed in DRG at E16 but it appears in these ganglia later in development (E20) and it is present in DRG of adult rats. In sagittal sections of whole embryos at very early stages of development we found that the onset of PYY mRNA expression is around day 11, when mRNA for PYY is found in the foregut. NPY and Y1-receptor mRNA are not detected in whole embryo sections until around day 14. Therefore, PYY mRNA expression precedes by 2-3 days the expression of mRNA for both NPY and the Y1 receptor. At E14, PYY mRNA is present in trigeminal ganglia and stomach. Our results suggest that PYY is not only a gut hormone but may also act as a neuropeptide with roles in the development of sensory neurons.

Animals↗
PubMed1993

Multiple loci for synapse protein SNAP-25 in the tetraploid goldfish.

The common goldfish Carassius auratus is tetraploid and has 100 chromosomes. We describe here goldfish cDNA clones for SNAP-25, a 200-amino-acid synaptosome-associated protein that has remained highly conserved during evolution. SNAP-25 occurs as a single-copy gene in mouse, chicken, and Drosophila melanogaster. Sequences of six distinct goldfish cDNA clones and Southern hybridizations show that the goldfish has three, or possibly four, SNAP-25 loci rather than two as expected. A gene duplication early in actinopterygian fish evolution gave rise to the loci SnapA and SnapB. The proteins SNAP-A and SNAP-B are 94% and 91% identical to the mouse protein but are only 91% identical to each other. SNAP-B has a larger number of unique amino acid replacements than SNAP-A and also has more dramatic replacements. The tetraploidization resulted in two SnapB loci whose divergence from each other is consistent with a tetraploidization event 15-20 million years ago. The presence of duplicate SnapA loci has not yet been possible to confirm, possibly because they are still very similar to each other. Two of the SnapA cDNA clones and one SnapB cDNA clone have frameshift mutations. As these aberrant alleles otherwise display high sequence identity to the functional alleles, they probably became nonfunctional recently. The findings of allelic variability and aberrant alleles emphasize the importance of characterizing multiple DNA clones in tetraploid species.

Amino Acid Sequence↗
PubMed1993

Evolutionary conservation of synaptosome-associated protein 25 kDa (SNAP-25) shown by Drosophila and Torpedo cDNA clones.

The neuron-specific proteins SNAP-25 (synaptosome-associated protein 25 kDa), synaptobrevin and syntaxin, are localized to presynaptic terminals in mammals and have been found to associate with proteins involved in vesicle docking and membrane fusion. We describe here SNAP-25 cDNA clones from the fruit fly Drosophila melanogaster and the ray Torpedo marmorata. In situ hybridization showed that SNAP-25 mRNA is exclusively found in brain and ganglia in Drosophila with a pattern suggesting expression in most neurons. The Drosophila and Torpedo proteins show 61 and 81% amino acid identity to mouse SNAP-25, a degree of conservation similar to that previously reported for synaptobrevin. None of the SNAP-25 sequences has a membrane-spanning region, but all contain a cluster of cysteine residues that can be palmitoylated for membrane attachment. SNAP-25 displays sequence similarity to syntaxin A and B. These data show that SNAP-25 and synaptobrevin, which are both implicated in vesicle docking and/or membrane fusion, have both been highly conserved during evolution. This supports the existence of a basic molecular machinery for synaptic vesicle docking in vertebrate and invertebrate synapses.

Amino Acid Sequence↗
PubMed1993

Biological origins of long-range correlations and compositional variations in DNA.

The occurrence of certain long-range correlations between nucleotides in DNA sequences of living organisms has recently been reported. The biological origin of these correlations was unknown. The correlations were proposed to be concerned with fractal structure and differences between intron-containing and intron-less sequences. We and others have reported that no consistent difference exists between intron-containing and intron-less sequences. In agreement with this, we demonstrate here that the long-range correlations are trivially equivalent to the varying ratio R between pyrimidines and purines (or any other nucleotide combinations) in different regions of a DNA sequence. Moreover, we show that this variation of R has simple biological explanations: Differences in base composition occur along most DNA sequences and are associated with (i) simple repeats (ii) differences in codon composition (due to the amino acid composition in the encoded protein), (iii) change of the direction of transcription (and thus also translation), and (iv) differences between protein- and rRNA-encoding segments. Seven biological examples are given.

Animals↗
PubMed1993

A proposed bovine neuropeptide Y (NPY) receptor cDNA clone, or its human homologue, confers neither NPY binding sites nor NPY responsiveness on transfected cells.

Receptors with seven transmembrane domains (7TM) constitute a large family of structurally and functionally related proteins which respond to various types of ligands. We describe here the cloning and expression of a human 7TM receptor, denoted hFB22 (human Fetal Brain 22), which is the homologue (92% amino acid identity) of a bovine receptor (LCR1) reported by others to bind neuropeptide Y (NPY) with a pharmacological profile of the Y3 receptor subtype. However, upon expression in COS1 (confirmed by Northern analysis), COS7 or CHO-K1 cells, the hFB22 receptor did not confer specific 125I-Bolton-Hunter-NPY, 3H-propionyl-NPY or 125I-peptide YY (PYY) binding sites, in either intact cells or in membrane preparations. Similarly, cells transfected with the corresponding bovine clone (LCR1) did not show specific NPY/PYY binding exceeding that resulting from endogenous binding sites; mock-transfected COS7 cells, used frequently for heterologous expression of receptors, were found to have endogenous specific 125I-NPY binding sites (Bmax = 112 fmol/mg protein; Kd = 0.25 nM). Moreover, the hFB22 transfected cells, when compared to control transfected cells, did not display de novo NPY- or PYY-induced second messenger responses, i.e., (1) inhibition of forskolin-stimulated cAMP accumulation or (2) 45Ca2+ influx. The presence of hFB22 mRNA was detected in several human neuroblastoma cell lines, none of which was found to express Y3-like NPY binding sites. hFB22 displays 39% amino acid sequence identity (in the transmembrane regions) to the human interleukin-8 receptor, and 32-36% amino acid identity to the human receptors of angiotensin II, bradykinin, and n-formylpeptide, but only 23% amino acid identity to the previously described human NPY/PYY receptor of the Y1 receptor subtype. Our results show that hFB22 and LCR1 do not encode NPY receptors, and their true ligand(s) remains to be identified.

Amino Acid Sequence↗
PubMed1993

Molecular cloning of a functional human thyrotropin-releasing hormone receptor.

A cDNA encoding the human thyrotropin-releasing hormone receptor (hTRH-R) was isolated from a human brain cDNA library. Screening of 1.2 million clones resulted in 2 candidates. The largest clone contained TRH-R homologous sequences starting in the third transmembrane domain and included a long 3' untranslated sequence. The smaller clone contained a potential start of the open reading frame, but was interrupted by an intron in the sixth transmembrane domain. The two clones had 497 bp of overlapping identical sequences and it was possible to assemble a complete cDNA thus restoring the assumed coding sequence. Electrophysiological studies of frog oocytes injected with in vitro transcribed mRNA showed TRH-specific inward currents, demonstrating that the reconstituted cDNA encoded a functional receptor. The predicted amino acid sequence of the hTRH-R protein showed high homology with the rat and mouse TRH-Rs with the exception of their C-terminal region. The human TRH-R gene seems to contain two introns.

Amino Acid Sequence↗