Ly-49D and Ly-49H associate with mouse DAP12 and form activating receptors

Several members of the Ly-49 receptor family inhibit NK cell-mediated lysis of targets expressing appropriate MHC class I molecules. Ly-49D and Ly-49H, two Ly-49 molecules that lack immunoreceptor tyrosine-based inhibitory motifs (ITIM) in their cytoplasmic domains, associate with mouse DAP12, a molecule that possesses an immunoreceptor tyrosine-based activation motif (ITAM). Cotransfection of either Ly-49D or Ly-49H with DAP12 induces surface expression of both Ly-49 and DAP12. The Ly-49/DAP12 complex was coimmunoprecipitated from the transfected cells, demonstrating a physical association of DAP12 with Ly-49D or Ly-49H in the plasma membrane. Stimulation of transfectants with Abs recognizing either Ly-49D or Ly-49H results in cellular activation, as assessed by induction of tyrosine phosphorylation of multiple cellular substrates.

Immunocytochemical localization of a putative inhibitory amino acid receptor subunit in the parasitic nematodes Haemonchus contortus and Ascaris suum

A rabbit antiserum was raised against a synthetic peptide corresponding to a region near the N-terminus of the Haemonchus contortus inhibitory amino acid receptor subunit, HG1. The antiserum recognized a recombinant form of the N-terminal domain of the subunit on Western blots and reacted with the ventral nerve cord of H. contortus in immunofluorescence experiments. Immunofluorescence was also detected in specific head neurons of H. contortus: these were tentatively identified as ring motor- and inter-neurons, plus a possible sensory neuron equivalent to the AQR cell of Caenorhabditis elegans. In the roundworm Ascaris suum, immunoreactivity was limited to the muscle arms, the post-synaptic component of the neuromuscular junction. The possible ligand of receptors containing the HG1 subunit is discussed in the light of this expression pattern.

Immunoreceptor tyrosine-based activation motif (ITAM), a unique module linking antigen and Fc receptors to their signaling cascades

Signal transduction by the T cell and B cell antigen receptors and by receptors for a variety of immunoglobulins' Fc region is strictly dependent on a receptor subunit cytoplasmic module termed immunoreceptor tyrosine-based activation motif (ITAM). This module exists in one or more copies in each of the receptor-associated signal-transducing molecules and it possesses two repeats of the consensus sequence Tyr-X-X-Leu/Ile spaced by six to eight amino acids. Receptor engagement is followed by a rapid and transient phosphorylation of tyrosine residues within their ITAMs, thereby creating temporary binding sites for Src homology 2 (SH2)-containing signaling molecules operating downstream of the activated receptor. The purpose of this review is to discuss recent findings on the functional role of ITAMs in antigen and Fc receptor-mediated signal transduction, with a particular emphasis on kinases operating upstream and downstream of the ITAMs.

Subthalamic nucleus modulates burst firing of nigral dopamine neurones via NMDA receptors

The role of the subthalamic nucleus in the burst firing of dopamine neurones of the substantia nigra was investigated using extracellular single unit recordings combined with pressure or iontophoretic micro-injections in anaesthetized rats. Inhibition of subthalamic neurones by pressure injection of gamma-aminobutyric acid (GABA) regularized the burst firing pattern in eight out of 17 dopamine neurones. Bicuculline injection near subthalamic neurones increased their firing rate and increased burst discharge in a subpopulation of dopamine neurones tested (34 out of 102). The increase was depressed by iontophoresis of the N-methyl-D-aspartate (NMDA) antagonist (+-)2-amino,5-phosphonopentanoic acid (AP-5), but not of the non-NMDA antagonist, 6-cyano,7-nitroquinoxaline-2,3-dione (CNQX). These data suggest that the subthalamic nucleus promotes burst discharge in a subpopulation of substantia nigra dopamine neurones via NMDA receptors.

mRNAs coding for neurotransmitter receptors in rabbit and rat visual areas

Levels of mRNAs encoding neurotransmitter receptors in the visual cortex, lateral geniculate nucleus, and superior colliculus of the rabbit and rat, and properties of the receptors expressed, were studied using Xenopus laevis oocytes. mRNA extracted from these areas was injected into the oocytes, which then acquired functional receptors. Electrical recordings of neurotransmitter-induced membrane currents reflect the relative amounts of mRNAs encoding the corresponding receptors. Receptors to gamma aminobutyric acid (GABA), kainate, glutamate, and serotonin exhibited uniformly high levels of expression, whereas expression of receptors to glycine and N-methyl-D-aspartate was uniformly low. In contrast, the expression of receptors to acetylcholine and substance P was highly non-uniform. Expression of acetylcholine receptors was high in oocytes injected with mRNA from the visual cortex, low for the lateral geniculate nucleus, and very low or absent for the superior colliculus. Conversely, the currents elicited by substance P were large in oocytes injected with superior colliculus mRNA, but were small or absent in oocytes injected with mRNAs from the other regions. Immunohistochemical analysis, at the light and electron microscopic levels, was used to localize choline acetyltransferase, the acetylcholine-synthesizing enzyme, and substance P-containing synaptic boutons in the three visual areas. Their presence closely paralleled the potency of mRNAs coding for acetylcholine and substance P receptors. The ability of rat mRNA, from each visual area, to induce neurotransmitter receptors was similar to that observed in the corresponding rabbit mRNAs. In addition to the marked differential distribution of mRNA encoding neurotransmitter receptors in the visual system, our findings reveal the probable existence of as yet uncharacterized receptors, whose new molecular forms may be revealed by further study. Our results also provide the basic information required for subsequent studies on the effect of monocular deprivation on the expression of neurotransmitter receptors in the visual system.

Molecular requirements for hapten binding to antibodies against glutamate and aspartate

Molecular requirements for hapten recognition by antibodies raised in rabbits against glutaraldehyde conjugates of L-glutamate and L-aspartate were determined in enzyme immunoassays by measuring the displacement of binding of glutamate and aspartate, respectively, by a large number of selected haptens to two anti-glutamate and two anti-aspartate sera. The results indicate that N-terminal modifications of the amino acids, such as the presence of an N-acetyl or N-carbamyl group or the addition of a second amino acid to form dipeptides with C-terminal glutamate or aspartate, are tolerated to variable degrees, more so by the aspartate than the glutamate antisera. The antibodies possess point-to-point recognition sites for the two carboxyl groups present in both amino acids. Strong shape complementarity between the amino acids and their respective binding sites is suggested by the lack of recognition of the appropriate D stereoisomers by any of the antibodies. Changes in the distance between the two carboxyl groups, or modification, replacement or loss of either or both carboxyl groups, strongly reduce or eliminate binding. Based on these results, we suggest that other antibodies raised to similar conjugates of these amino acids are likely to share similar recognition characteristics. In addition, the results provide a rational background for the evaluation of antibody specificity and the interpretation of results in immunocytochemical studies using antisera to glutamate and aspartate.