GABA(A) receptor cell surface number and subunit stability are regulated by the ubiquitin-like protein Plic-1.

Controlling the number of functional gamma-aminobutyric acid A (GABA(A)) receptors in neuronal membranes is a crucial factor for the efficacy of inhibitory neurotransmission. Here we describe the direct interaction of GABA(A) receptors with the ubiquitin-like protein Plic-1. Furthermore, Plic-1 is enriched at inhibitory synapses and is associated with subsynaptic membranes. Functionally, Plic-1 facilitates GABA(A) receptor cell surface expression without affecting the rate of receptor internalization. Plic-1 also enhances the stability of intracellular GABA(A) receptor subunits, increasing the number of receptors available for insertion into the plasma membrane. Our study identifies a previously unknown role for Plic-1, a modulation of GABA(A) receptor cell surface number, which suggests that Plic-1 facilitates accumulation of these receptors in dendritic membranes.

The protein MAP-1B links GABA(C) receptors to the cytoskeleton at retinal synapses.

The ionotropic type-A and type-C receptors for the neurotransmitter gamma-aminobutyric acid (GABA(A) and GABA(C) receptors) are the principal sites of fast synaptic inhibition in the central nervous system, but it is not known how these receptors are localized at GABA-dependent synapses. GABA(C) receptors, which are composed of rho-subunits, are expressed almost exclusively in the retina of adult vertebrates, where they are enriched on bipolar cell axon terminals. Here we show that the microtubule-associated protein 1B (MAP-1B) specifically interacts with the GABA(C) rho1 subunit but not with GABA(A) receptor subunits. Furthermore, GABA(C) receptors and MAP-1B co-localize at postsynaptic sites on bipolar cell axon terminals. Co-expression of MAP-1B and the rho1 subunit in COS cells results in a dramatic redistribution of the rho1 subunit. Our observations suggest a novel mechanism for localizing ionotropic GABA receptors to synaptic sites. This mechanism, which is specific for GABA(C) but not GABA(A) receptors, may allow these receptor subtypes, which have distinct physiological and pharmacological properties, to be differentially localized at inhibitory synapses.

GABA(A)-receptor-associated protein links GABA(A) receptors and the cytoskeleton.

Type-A receptors for the neurotransmitter GABA (gamma-aminobutyric acid) are ligand-gated chloride channels that mediate inhibitory neurotransmission. Each subunit of the pentameric receptor protein has ligand-binding sites in the amino-terminal extracellular domain and four membrane-spanning regions, one of which forms a wall of the ion channel. Each subunit also has a large intracellular loop that may be a target for protein kinases and be required for subcellular targeting and membrane clustering of the receptor, perhaps by anchoring the receptor to the cytoskeleton. Neurotransmitter receptors need to be positioned in high density in the cell membrane at sites postsynaptic to nerve terminals releasing that neurotransmitter. Other members of the superfamily of ligand-gated ion-channel receptors associate in postsynaptic-membrane clusters by binding to the proteins rapsyn or gephyrin. Here we identify a new cellular protein, GABA(A)-receptor-associated protein (GABARAP), which can interact with the gamma2 subunit of GABA(A) receptors. GABARAP binds to GABA(A) receptors both in vitro and in vivo, and co-localizes with the punctate staining of GABA(A) receptors on cultured cortical neurons. Sequence analysis shows similarity between GABARAP and light chain-3 of microtubule-associated proteins 1A and 1B. Moreover, the N terminus of GABARAP is highly positively charged and features a putative tubulin-binding motif. The interactions among GABA(A) receptors, GABARAP and tubulin suggest a mechanism for the targeting and clustering of GABA(A) receptors.

Alterations in classical cadherins associated with progression in ulcerative and Crohn's colitis.

Human colitis is a condition associated with a spectrum of altered morphologic changes and cellular adhesion. The role of cadherins, which are powerful morphoregulatory cell adhesion molecules, in colitis is provocative and as yet unknown. Herein, we present results that suggest a strong correlation between the deregulation of two cadherin molecules, E- and P-cadherins, and the progression of human colitis. We examined the expression and structural integrity of E- and P-cadherins in inflamed, dysplastic, or neoplastic human ulcerative colitis (UC) (n=58), human Crohn's colitis (n = 30), and normal tissue (n = 20) to assess cadherin function in normal and abnormal epithelium. E-cadherin is strongly expressed in normal colorectal epithelium, whereas in left-sided UC it is either down-regulated or has a single-base pair mutation in exon 4 resulting in an amino acid alteration (6 of 58 UC cases). By contrast, P-cadherin is dramatically up-regulated in both Crohn's disease and ulcerative colitis and especially in dysplastic ulcerative tissue. In vitro transfected SW-480 colorectal cells containing E-cadherin mutations identical to those in vivo were associated with increased spontaneous disaggregation compared with cells transfected with wild-type E-cadherin. Based on this evidence, we hypothesize that a small subset of colorectal cells expressing mutant E-cadherin are associated with widespread ulceration, whereas those expressing P-cadherin are associated with a rapidly dividing immature phenotype that includes dysplasia. The differential expression of mutated and wild-type cadherins examined herein are associated with a broad spectrum of abnormal epithelial phenotypes, lymphocyte integrin binding, and resistance to denudation, as is seen in the colitis adenocarcinoma sequence.

Neuronal expression of the 5HT3 serotonin receptor gene requires nuclear factor 1 complexes.

The 5HT3 receptor (5HT3R) is a serotonin-gated ion channel whose expression is restricted to a subset of cells within the central and peripheral nervous systems. In vitro analysis shows that a small proximal region of the TATA-less 5HT3R promoter is sufficient to direct neuronal-specific reporter gene expression. Three potential regulatory elements conserved between the mouse and human genes were identified within this proximal promoter, two of which are known sites for the ubiquitously expressed factors Sp1 and nuclear factor 1 (NF1). Surprisingly, mutation of the NF1 binding site abolished all reporter activity in cell transfection studies, suggesting that this element is essential for neuronal-specific transcriptional activity of the 5HT3R. Furthermore, a complex of neuronal proteins that includes a member(s) of the NF1 family binds to this site, as shown by gel mobility super shift and DNaseI footprinting analyses. Although NF1 has been proposed to mediate basal transcription of many ubiquitously expressed genes, our data suggest that a member of the NF1 transcription factor family participates in neuronal-specific gene expression by promoting interactions with other regulatory factors found in sensory ganglia.

False categories in cognition: the Not-the-Liver fallacy.

This paper reports on an increasingly frequent error committed in cognition research that at best slows progress, and at worse leads to self-perpetuating false claims and misguided research. The error involves how we identify meaningful processes and categories on the basis of data. Examples are given from three areas of cognition: (1) memory, where the misconception has fueled the popular implicit/explicit categories, (2) perception, where the misconception is used to re-evaluate the classic what/where division, and (3) motor skills, where it is used to draw conclusions from patients with Huntington's disease. Reasons for the prevalence of this error, how it relates to double dissociations, and what it suggests about scientific reasoning are offered.

Molecular biology of pituitary development and disease.

The major endocrine cell types of the anterior and intermediate pituitary arise in sequential order during development. Our laboratory seeks to understand the molecular basis for different lineages among these cell types. Previous data from our group and others have shown that the POU-domain factor, Pit-1, and the orphan nuclear receptor, SF-1, are critical in the specification and maintenance of these cell types. The analysis of naturally occurring mutations revealed that Pit-1 is needed for development of three cell types, the thyrotropes (thyroid-stimulating hormone), somatotropes (growth hormone), and lactotropes (prolactin). Recently, a genetically engineered mouse mutant demonstrated that SF-1 is required for the maintenance of the gonadotrope (luteinizing hormone/follicle-stimulating hormone) cellular phenotype. To date, a similar factor for the corticotrope and melanotrope lineages expressing propiomelanocortin (POMC) has not been identified. Surprisingly, the serotonin (5-HT) neurotransmitter receptor 5-HT3 was found to be expressed in the anterior and intermediate lobes of the developing rodent pituitary. We are using this new marker to examine the molecular basis of the POMC lineages.

Constraints on perceptual learning: objects and dimensions.

The article addresses two questions about perceptual learning: What are the circumstances which produce learning? What is the content of learning? For each question, a critical principle is suggested: (1) Objects are constrained to behave in certain ways. If a violation is detected, an internal malfunction is assumed and subsequently corrected. (2) Learning involves mappings between entire perceptual dimensions rather than associations between individual stimuli. The principles are applied to two phenomena: the classic adaptation to prism distorted vision and the more recent, but equally elusive, McCollough effect. The view suggests a new interpretation of the McCollough effect and accounts for findings difficult to account for in other interpretations including which stimuli can successfully lead to contingent after-effects, the outcome of correlation manipulations, and why the effect exists at all. In addition, the phenomenon is linked to prism adaptation, usually regarded as a distinct type of plasticity. In general, the view advanced is that the two principles help distinguish perceptual learning from other types of learning processes.

The McCollough effect: dissociating retinal from spatial coordinates.

Three experiments were conducted to dissociate the perceived orientation of a stimulus from its orientation on the retina while inducing the McCollough effect. In the first experiment, the typical contingency between color and retinal orientation was eliminated by having subjects tilt their head 90 degrees for half of the induction trials while the stimuli remained the same. The only relation remaining was that between color and the perceived or spatial orientation, which led to only a small contingent aftereffect. In contrast, when the spatial contingency was eliminated in the second experiment, the aftereffect was as large as when both contingencies were present. Finally, a third experiment determined that part of the small spatial effect obtained in the first experiment could be traced to hidden higher order retinal contingencies. The study suggested that even under optimal conditions the McCollough effect is not concerned with real-world properties of objects or events. Implications for several classes of theories are discussed.

Perceptual and cognitive spatial learning.

Ss were taught novel mappings between visual space and motor space with either a variant on a prism adaptation paradigm (Experiments 1 and 2) or a nonperceptual cognitive task (Experiments 3 and 4). First, discrimination training specified that 1 visual location required a new pointing response but another location did not. This led to unusual generalization unlike typical generalization decrement. Second, training at 9 locations specified that 1 location required a new response but that the remaining 8 did not. This simple isolation mapping was unlearnable and instead a flat function fit through all of space. In contrast, for the cognitive paradigm, not only was isolation of one region of space easily learned, it was the preferred pattern of generalization. Implications for perceptual learning, as well as the qualitative distinctions between perceptual and cognitive learning, are discussed.

HEX: a novel homeobox gene expressed during haematopoiesis and conserved between mouse and human.

We describe the cloning of a novel homeodomain-containing gene, which is highly conserved between mouse and human. The human cDNA was initially isolated from human haematopoietic tissue and denoted HEX (haematopoietically expressed homeobox). Sequence analysis of the coding sequences from mouse and the partial cDNA from human shows that the homeodomain is most closely related to those of the HIx and HOX11 proteins. The HEX gene is present as a single copy in the human genome. Analysis of murine genomic DNA shows, in addition to an intron-containing gene homologous to HEX, the presence of a processed copy of the gene which has arisen within the last few million years. Analysis of human and murine haematopoietic cells and cell lines, revealed expression of the HEX gene in multipotential progenitors, as well as cells of the B-lymphocyte and myeloid lineages. However HEX was not expressed in T-lymphocytes or erythroid cells. This pattern of HEX gene expression suggests that it may play a role in haematopoietic differentiation.