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Biomedical subjects

J M Allen

Publications and source records attributed to J M Allen.

At least 19 recordsLinked to original sources
PubMed1992

Functional dissection of the lck proximal promoter.

The lck gene encodes a protein tyrosine kinase that participates in lymphocyte-specific signal transduction pathways. Previous studies have established that lck transcription is regulated by two distinct promoter elements termed proximal (or 3') and distal (or 5'). The proximal promoter is active almost exclusively in thymocytes and becomes inactive later during T-cell maturation. To dissect the mechanisms responsible for lck gene regulation, we generated transgenic animals bearing 5' truncations in the proximal promoter element. Sequences between -584 and +37 with respect to the proximal promoter transcription start site act to direct tissue-specific and temporally correct transcription of either a tagged version of the lck gene itself or a heterologous reporter sequence (lacZ). This region contains binding sites for at least five distinct nuclear proteins, of which one is found only in cells that support proximal lck promoter activity and a second appears only in nonexpressing cells. Interestingly, the transcribed region of the lck gene contains positive control elements that can substantially boost expression from minimal (-130 bp) proximal promoter constructs. These results provide a basis for the biochemical dissection of transcriptional regulators that act at defined points during T-cell development.

Animals↗
PubMed1991

Developmental regulation of lck gene expression in T lymphocytes.

In the mouse and human, mRNA transcripts encoding the lymphocyte-specific protein tyrosine kinase p56lck are derived from two separate promoters resulting in heterogeneity in the 5' untranslated region sequence. The proximal promoter lies just 5' to the coding region for the gene and is active only in thymocytes. In contrast, the distal promoter lies 34 kilobases (kb) 5' in the human, and is active both in thymocytes and mature peripheral T cells. As previously reported, transgenic mice bearing functional proximal promoter sequence juxtaposed with the SV40 large T antigen gene invariably develop lymphoid tumors confined to the thymus. In the current work, transgenic mice bearing a 2.6-kb fragment of the human distal promoter fused to the SV40 large T antigen gene express large T antigen in thymocytes and in peripheral lymphoid cells, and develop tumors of both the thymus and the peripheral lymphoid organs. The ability of the human distal promoter to function appropriately in transgenic mice is consistent with the strong similarity observed between the mouse and human distal promoter sequences. With the exception of a single short interval that serves as a target for binding of nuclear factors, significant sequence similarity is not seen when the distal and proximal promoter sequences are compared. Hence, developmentally regulated, lineage-specific transcription of the lck gene is mediated by distinct promoter sequences that appear to be capable of functioning independently.

Animals↗
PubMed1991

Decreased beta 2-adrenergic receptor mRNA expression in receptor-deficient S49 lymphoma cells.

Many variants of the S49 mouse lymphoma cell have been isolated along the pathway of cyclic AMP generation and response. Two such variants, beta p and beta d, were isolated by Johnson and colleagues and described in 1979 [Mol. Pharmacol. 15:16-27 (1979)]. The beta p and beta d variants express one half and one quarter, respectively, of the wild-type number of beta 2-adrenergic receptors. This observation has now been extended through the use of DNA-excess solution hybridization. Using this exquisitely sensitive technique for quantitation of gene and mRNA, we have been able to demonstrate that the beta 2-adrenergic receptor-deficient variant cells contain the same quantity of the beta 2-adrenergic receptor gene as the wild-type cells. In contrast, the beta 2-adrenergic receptor-deficient variant cells express reduced quantities of beta 2-adrenergic receptor-specific mRNA. The amount of beta 2-adrenergic receptor-specific mRNA correlates very well with the reduction in receptor expression in these cells. Both gene and mRNA in the wild-type and variant cells appear to be the same size, as judged by Southern and Northern analysis. Thus, the diminution of beta 2-adrenergic receptors in the beta p and beta d variants appears to reflect primarily the relative paucity of gene transcripts in the variant cells. These data imply that variations in cellular content of beta 2-adrenergic receptor mRNA, which may occur among closely related cells, is one explanation for differences in receptor number.

Animals↗
PubMed1990

Neuropeptide Y (NPY)-containing nerves in mammalian ureter.

The distribution of neuropeptide Y in the ureter of the rat, rabbit, and man has been determined by radioimmunoassay and chromatographic analysis of the tissue extract. The localization of neuropeptide Y-immunoreactivity has been identified by immunocytochemistry. A regional distribution of neuropeptide Y was found; highest concentrations being present in the ureterovesical junction. Throughout the ureter, neuropeptide Y-immunoreactive nerve fibers were identified to surround the blood vessels and a few plexuses of neuropeptide Y-containing nerves were present within the muscle layers. Neuropeptide Y was not present within ganglion cells. Treatment of rats with 6-hydroxydopamine resulted in a significant reduction of neuropeptide Y concentrations in the upper, middle, and lower thirds of the ureter. This depletion in extractable neuropeptide Y was associated with morphologic changes typical of axonal degeneration of the neuropeptide Y-containing nerve fibers.

Animals↗
PubMed1990

Molecular structure of neuropeptide Y.

The original description of NPY following its isolation commented on its homology to the pancreatic polypeptide family of peptides. This homology is extended to the mRNA sequences and the genomic structure, suggesting that this family has arisen as a result of gene duplication. However, each member demonstrates remarkable specificity in its expression within tissue types. The expression of the NPY gene is thus controlled by, as yet undefined, factors regulating to neural cells. The level of expression within cells is dependent on nerve growth factor. However, other factors, such as the rate of processing of the precursor, may be involved in regulation of the stored concentrations of the peptide product.

Amino Acid Sequence↗
PubMed1990

Nerve-mediated contractions of sheep mesenteric lymph node capsules.

1. Isometric tension was recorded in vitro from strips cut from the capsules of mesenteric lymph nodes of sheep. 2. One minute periods of field stimulation at frequencies of 1, 2, 4, 8 and 16 Hz (pulse duration, 0.3 ms) elicited tonic contractions of increasing force and duration. The stimulus frequency-response relationship began to flatten out at frequencies greater than 4 Hz, where the response was already 72% of that at 16 Hz. 3. The response to field stimulation was abolished by tetrodotoxin (1 microM). 4. Phentolamine, rauwolscine and prazosin (all 1 microM) reduced the response to field stimulation, while desipramine (1 microM), potentiated it. 5. Atropine (1 microM) was without effect on the response. 6. These results suggest that sheep mesenteric lymph node capsules have a noradrenergic innervation which modulates their tone via an action on alpha-adrenoceptors.

Adrenergic alpha-Antagonists↗
PubMed1989

Sex differences in vasoactive intestinal peptide (VIP) concentrations in the anterior pituitary and hypothalamus of rats.

Recent evidence suggests that vasoactive intestinal peptide (VIP), a putative prolactin (PRL)-releasing factor, is both synthesized and released by anterior pituitary cells, to act as a paracrine or autocrine factor. We have investigated the hypothesis that hypothalamic or pituitary VIP levels differ in male and female rats, since neuroendocrine control of PRL is sexually differentiated. Opposite sex differences were found in the hypothalamus and anterior pituitary. Random-cycle female rats had one-third higher VIP levels in the hypothalamus than males. In contrast, anterior pituitary VIP levels were 3 times as high in male rats as in females. Median eminence VIP levels were similarly low in both sexes. These results support a possible role of VIP in the sexually dimorphic regulatory mechanisms of PRL secretion. Moreover, demonstration that hypothalamic and pituitary VIP levels vary in opposite directions suggests that VIP is differentially regulated at the two sites.

Animals↗
PubMed1989

Neuropeptide Y (NPY) and vasopressin (AVP) in the hypothalamo-neurohypophysial axis of salt-loaded or Brattleboro rats.

A close anatomical relationship between nerve terminals containing neuropeptide Y (NPY) and vasopressin (AVP) has been demonstrated in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). Furthermore, injections of NPY into the SON increased plasma concentrations of AVP in the rat. These data suggest a potential involvement of hypothalamic NPY in fluid homeostasis in the rat. Therefore, we have studied the effect of elevated plasma osmolality on the concentration of NPY and AVP in the hypothalamus and neurointermediate lobe (NIL) of the pituitary gland. Furthermore, we measured the concentration of NPY in the AVP-deficient Brattleboro rat, which suffers from diabetes insipidus and hyperosmolality. Salt-loading increased plasma osmolality and the concentration of AVP from 2.0 +/- 0.5 to 4.1 +/- 0.6 pg/ml after 7 days. The concentration of NPY in the NIL doubled after 7 days of salt-loading, from 7.9 +/- 0.6 ng/mg protein to 15.2 +/- 1.4 ng/mg protein, whereas AVP concentrations fell from 2285.7 +/- 210.9 ng/mg protein to 187.5 +/- 2.5 ng/mg protein. AVP concentrations in the ME increased transiently after 2 days of salt-loading and returned to control levels after 7 days. In contrast, NPY concentrations in the ME were unchanged at 2 days and were increased 61% after 7 days. NPY concentrations also were significantly elevated after 7 days of salt-loading in the preoptic area (POA) and mediobasal hypothalamus (MBH). The concentration of NPY in the NIL of the homozygous Brattleboro rat was 2-fold greater than in the heterozygous Brattleboro rat and 4-fold greater than in Sprague-Dawley rats used as controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Isolation and expression of functional high-affinity Fc receptor complementary DNAs.

Human and murine mononuclear phagocytes express a high-affinity receptor for immunoglobulin G that plays a central role in macrophage antibody-dependent cellular cytotoxicity and clearance of immune complexes. The receptor (FcRI) may also be involved in CD4-independent infection of human macrophages by human immunodeficiency virus. This report describes the isolation of cDNA clones encoding the human FcRI by a ligand-mediated selection technique. Expression of the cDNAs in COS cells gave rise to immunoglobulin G binding of the expected affinity and subtype specificity. RNA blot analysis revealed expression of a 1.7-kilobase transcript in macrophages and in cells of the promonocytic cell line U937 induced with interferon-gamma. The extracellular region of FcRI consists of three immunoglobulin-like domains, two of which share homology with low-affinity receptor domains.

Amino Acid Sequence↗
PubMed1989

The effects of cholinergic and serotoninergic drugs on motility in vitro of Haplometra cylindracea (Trematoda: Digenea).

The spontaneous activity of the somatic muscle of the amphibian lung fluke, Haplometra cylindracea has been recorded in vitro, using an isometric force transducer system. Normal movement consisted of a continuous series of regular contractions which were maintained for over 4 h. Acetylcholine (ACh) inhibited motility at a concentration of 1 X 10(-3)M induced a flaccid paralysis. A similar response occurred with the cholinomimetric drugs, carbachol and nicotine, although in these instances the inhibition was less easily reversed by washing with frog Ringer. The inhibitory effect of ACh was blocked by d-tubocurarine but not by atropine. Serotonin (5-HT) caused an increase in the frequency and amplitude of contractions and the effect was blocked by methysergide. No uniform response was observed with 3-hydroxytryptamine (3-HT), but both reserpine and fluoxetine inhibited worm movement. Results suggest that the somatic musculature of the worm is controlled, at least in part, by an inhibitory cholinergic and an excitatory serotoninergic system.

Acetylcholine↗