Regulation of alternative splicing of tau exon 10

The neuronal microtubule-associated protein tau is abnormally hyperphosphorylated and aggregated into neurofibrillary tangles in the brains of individuals with Alzheimer’s disease and related neurodegenerative disorders. The adult human brain expresses six isoforms of tau generated by alternative splicing of exons 2, 3, and 10 of its pre-mRNA. Exon 10 encodes the second microtubule-binding repeat of tau. Its alternative splicing produces tau isoforms with either three or four microtubule-binding repeats, termed 3R-tau and 4Rtau. In the normal adult human brain, the level of 3R-tau is approximately equal to that of 4R-tau. Several silent and intronic mutations of the tau gene associated with FTDP-17T (frontotemporal dementia with Parkinsonism linked to chromosome 17 and specifically characterized by tau pathology) only disrupt exon 10 splicing, but do not influence the primary sequence of the tau protein. Thus, abnormal exon 10 splicing is sufficient to cause neurodegeneration and dementia. Here, we review the regulation of tau exon 10 splicing by cis-elements and trans-factors and summarize all the mutations associated with FTDP-17T and related tauopathies. The findings suggest that correction of exon 10 splicing may be a potential target for tau exon 10 splicing-related tauopathies.     

Assessment factors associated with premature psychotherapy termination.

Characteristics of patients accepted for both intensive psychotherapy and psychoanalysis were rated during their initial assessments. Twenty cases that terminated prematurely (most within the first month) were compared with twenty cases that continued in therapy. While neither specific diagnosis, type of insight therapy, nor gender of the patient or therapist was a reliable predictor of premature termination, it was found that psychodynamic and environmental assessment factors significantly differed between these two groups. In those patients who eventually dropped out, specific ego deficits, primarily introspection, frustration tolerance, impulse control, and motivation, were rated as significantly more impaired. The therapists' negative feelings toward their prospective patients and the patients' hostility toward past caretakers and present life circumstances were also associated with premature termination.     

Factors associated with premature termination from outpatient treatment

A variety of demographic and clinical data collected on 142 new patients treated in an adult psychiatric outpatient clinic were analyzed to determine factors that discriminated between patients who terminated treatment prematurely during the first eight months of therapy and those who did not. High levels of paranoid ideation, lack of health insurance, and living less than 15 miles from the clinic were significantly associated with premature termination. Those factors were combined with three others--substance abuse, divorced marital status, and absence of fee reduction--in a probit regression model that correctly predicted the incidence of premature termination in 75 percent of the patients. The results suggest that patients who may be at risk for premature termination of outpatient therapy can be identified early in the course of their treatment.     

Evidence for medullary projections of the intercostal nerve-elicited inspiratory termination

This study hypothesized that the ICN-elicited inspiratory termination reflex required synaptic activation in two distinct regions of the ventral respiratory group (VRG): (1) transitional (tVRG), and (2) pre-B?tzinger complex (pre-B?tC). Data from adult cats indicate that axons of passage associated with the ICN-elicited termination reflex traverse tVRG, but that relevant synaptic processing does not occur in this region. Furthermore, data indicate that neither synaptic nor axonal transmission within the pre-B?tC is required for the SLN- or ICN-elicited termination reflex.     

Pharmacological characterization of purinergic inhibitory neuromuscular transmission in the human colon

Background In the present study, we further characterize the purinergic receptors mediating the inhibitory junction potential (IJP) and smooth muscle relaxation in the human colon using a new, potent and selective agonist (MRS2365), and antagonists (MR2279 and MRS2500) of the P2Y₁ receptor. The P2Y₁₂ antagonist AR‐C66096 was tested as well. Using this pharmacological approach, we tested whether β‐nicotinamide adenine dinucleotide (β‐NAD) fulfilled the criteria to be considered an inhibitory neurotransmitter in the human colon. Methods We carried out muscle bath and microelectrode experiments on circular strips from the human colon and calcium imaging recordings on HEK293 cells, which constitutively express the human P2Y₁ receptor. Key Results Both the fast component of IJP and non‐nitrergic relaxation was concentration‐dependently inhibited by MRS2279 and MRS2500. This antagonism was confirmed in HEK293 cells. However, AR‐C66096 did not modify either inhibitory response. Adenosine 5′‐Ο‐2‐thiodiphosphate and MRS2365 caused a smooth muscle hyperpolarization and transient inhibition of spontaneous motility that was antagonized by MRS2279 and MRS2500. β‐Nicotinamide adenine dinucleotide inhibited the spontaneous motility (IC₅₀ = 3.3 mmol L^?1). Nevertheless, this effect was not antagonized by high concentrations of P2Y₁ antagonists. Conclusions & Inferences Inhibitory purinergic neuromuscular transmission in the human colon was pharmacologically assessed by the use of new P2Y₁ receptor antagonists MRS2179, MRS2279, and MRS2500. The rank order of potency of the P2Y₁ antagonists is MRS2500 > MRS2279 > MRS2179. We found that β‐NAD partially fulfills the criteria to be considered an inhibitory neurotransmitter in the human colon, but the relative contribution of each purine (ATP/ADP vsβ‐NAD) requires further studies.     

Progress in understanding of inhibitory purinergic neuromuscular transmission in the gut

Recent studies with genetic deletion of P2Y1 receptor (P2Y1?/?) have clinched its role in enteric purinergic inhibitory neurotransmission and suggested that β‐NAD may be the purinergic inhibitory neurotransmitter in the colon. In this issue of the Journal, Gil and colleagues extend their earlier observations to the cecum and gastric antrum, showing that P2Y1 receptor mediated purinergic inhibition may be a general phenomenon in the gut. However, the authors made an unexpected observation in contrast with their earlier findings in the colon that neither the selective P2Y1 receptor antagonist MRS2500, nor P2Y1 receptor deletion, blocked the hyperpolarizing action of β‐NAD in the cecum. These observations suggest that β‐NAD may be the purinergic inhibitory neurotransmitter in the colon, but not in the cecum. This group had previously reported that the selective P2Y1 receptor antagonist MRS 2179 suppressed the hyperpolarizing action of ATP or ADP. Further studies are now needed to determine whether the hyperpolarizing actions of ATP and ADP are suppressed by the more potent P2Y1 antagonist MRS2500, and in P2Y1?/? mutants to test the intriguing possibility that different purines serve as purinergic inhibitory neurotransmitters in the colon and cecum and perhaps in different parts of the gut. Studies in P2Y1?/? mice will resolve other issues in purinergic neurotransmission including cellular localization of the β‐NAD or ATP‐activated P2Y1 receptors on either smooth muscle cells or PDGFRα+ fibroblast‐like cells, relationship of purinergic to nitrergic neurotransmission and understanding the physiological and clinical importance of purinergic transmission in gastrointestinal motility and its disorders.     

Evidence for case-to-case transmission of Creutzfeldt-Jakob disease

Three cases of probable iatrogenic transmission of Creutzfeldt-Jakob disease by neurosurgery are detailed together with a cluster of three cases in Eastern England possibly connected by dental procedures, and the development of Creutzfeldt-Jakob disease in a patient who had been in social contact with a familial case.     

Evidence for the involvement of purinergic P2X receptors in outer retinal processing

Extracellular ATP mediates fast excitatory neurotransmission in many regions of the central nervous system through activation of P2X receptors. Although several P2X receptor subunits have been identified in the mammalian retina, little is known about the functional role of these receptors in retinal signalling. The purpose of the present study was to investigate whether purinergic P2X(7) receptors are involved in outer retinal processing by assessing receptor localization, degradation of extracellular ATP and the effect of functional activation of P2X(7) receptors on the electroretinogram (ERG). Using light and electron microscopy, we demonstrated that P2X(7) receptors are expressed postsynaptically on horizontal cell processes as well as presynaptically on photoreceptor synaptic terminals in both the rat and marmoset retina. Using an enzyme cytochemical method, we showed that ecto-ATPases are active in the outer plexiform layer of the rat retina, providing a mechanism by which purinergic synaptic transmission can be rapidly terminated. Finally, we evaluated the role of P2X(7) receptors in retinal function by assessing changes to the ERG response of rats after intravitreal delivery of the P2X(7) receptor agonist benzoyl benzoyl ATP (BzATP). Intravitreal injection of BzATP resulted in a sustained increase (up to 58%) in the amplitude of the photoreceptor-derived a-wave of the ERG. In contrast, BzATP caused a transient reduction in the rod- and cone-derived postreceptoral responses. These results provide three lines of evidence for the involvement of extracellular purines in outer retinal processing.     

Activity-dependent regulation of alternative splicing patterns in the rat brain

Alternative splicing plays an important role in the expression of genetic information. Among the best understood alternative splicing factors are transformer and transformer-2, which regulate sexual differentiation in Drosophila. Like the Drosophila genes, the recently identified mammalian homologues are subject to alternative splicing. Using an antibody directed against the major human transformer-2 beta isoform, we show that it has a widespread expression in the rat brain. Pilocarpine-induced neuronal activity changes the alternative splicing pattern of the human transformer-2-beta gene in the brain. After neuronal stimulation, a variant bearing high similarity to a male-specific Drosophila tra-2179 isoform is switched off in the hippocampus and is detectable in the cortex. In addition, the ratio of another short RNA isoform (htra2-beta2) to htra2-beta1 is changed. Htra2-beta2 is not translated into protein, and probably helps to regulate the relative amounts of htra2-beta1 to beta3. We also observe activity-dependent changes in alternative splicing of the clathrin light chain B, c-src and NMDAR1 genes, indicating that the coordinated change of alternative splicing patterns might contribute to molecular plasticity in the brain.     

Conservation of expression and alternative splicing in the prosaposin gene

Prosaposin is the precursor of four lysosomal activator molecules known as saposins A, B, C and D. It is also secreted and was proposed to be a neurotrophic factor. The neurotrophic function was attributed to the amino terminus of saposin C. In man, mouse and rat prosaposin is transcribed to two major isoforms differing in the inclusion of 9 bps of exon 8 within the saposin B domain. In the present study, we show that there is evolutionary conservation of the prosaposin structure and alternative splicing in chick and zebrafish as well. Moreover, there is conservation in prosaposin expression as tested immunohistochemically in the mouse and chick developing brain. We developed a sensitive assay to quantitate the prosaposin alternatively spliced forms. Our results indicate that, in mouse brain, skeletal and cardiac muscle the exon 8-containing RNA is most abundant, while it is almost absent from visceral and smooth muscle-containing organs. We observed temporal and differential expression of the alternatively spliced prosaposin mRNAs in mouse and chick brain as well as during development. The elevation in the abundance of exon 8-containing prosaposin RNA during mouse and chick brain development may suggest a role for the exon 8-containing prosaposin form in this process.