Regulation of Ich-1 pre-mRNA alternative splicing and apoptosis by mammalian splicing factors

The importance of alternative splicing in regulating apoptosis has been suggested by findings of functionally antagonistic proteins generated by alternative splicing of several genes involved in apoptosis. Among these, Ich-1 (also named as caspase-2) encodes a member of the caspase family of proteases. Two forms of Ich-1 are produced as a result of alternative splicing: Ich-1L, which causes apoptosis, and Ich-1S, which prevents apoptosis. The precise nature of Ich-1 alternative splicing and its regulation remain unknown. Here, we show that the production of Ich-1L and Ich-1S transcripts results from alternative exclusion or inclusion of a 61-bp exon. Several splicing factors can regulate Ich-1 splicing. Serine-arginine-rich proteins SC35 and ASF/SF2 promote exon skipping, decreasing the ratio of Ich-1S to Ich-1L transcripts; whereas heterogeneous nuclear ribonucleoprotein A1 facilitates exon inclusion, increasing this ratio. Furthermore, in cultured cells, SC35 overexpression increases apoptosis; whereas heterogeneous nuclear ribonucleoprotein A1 overexpression decreases apoptosis. These results provide the first direct evidence that splicing factors can regulate Ich-1 alternative splicing and suggest that alternative splicing may be an important regulatory mechanism for apoptosis.

Initiation of spontaneous epileptiform activity in the neocortical slice

Cortical local circuitry is important in epileptogenesis. Voltage-sensitive dyes and fast imaging were used to visualize the initiation of spontaneous paroxysmal events in adult rat neocortical slices. Although spontaneous paroxysmal events could start from anywhere in the preparation, optical imaging revealed that all spontaneous events started at a few confined initiation foci and propagated to the whole preparation. Multielectrode recording over hundreds of spontaneous events revealed that often two or three initiation foci coexisted in each preparation (n = 10). These foci took turns being dominant; the dominant focus initiated the majority of the spontaneous paroxysmal events during that period. The dominant focus and dynamic rearrangement of foci suggest that the initiation of spontaneous epileptiform events involves a local multineuronal process, perhaps with potentiated synapses.

Regulation of taurine biosynthesis and its physiological significance in the brain

Cysteine sulfinic acid decarboxylase (CSAD), the rate-limiting enzyme in taurine biosynthesis, was found to be activated under conditions that favor protein phosphorylation and inactivated under conditions favoring protein dephosphorylation. Direct incorporation of 32P into purified CSAD has been demonstrated with [gamma 32P]ATP and PKC, but not PKA. In addition, the 32P labeling of CSAD was inhibited by PKC inhibitors suggesting that PKC is responsible for phosphorylation of CSAD in the brain. Okadaic acid had no effect on CSAD activity at 10 microM suggesting that protein phosphatase-2C (PrP-2C) might be involved in the dephosphorylation of CSAD. Furthermore, it was found that either glutamate- or high K(+)-induced depolarization increased CSAD activity as well as 32P-incorporation into CSAD in neuronal cultures, supporting the notion that the CSAD activity is endogenously regulated by protein phosphorylation in the brain. A model to link neuronal excitation, phosphorylation of CSAD and increase in taurine biosynthesis is proposed.

Prenatal diagnosis of Apert syndrome

Apert syndrome (AS) is clinically characterized by typical facial features and symmetrical syndactyly of the digits. AS is inherited as an autosomal dominant trait. Recently, a fibroblast growth factor receptors 2 (FGFR2) mutation, either C934G or C937G, was identified in exon IIIa. Our report documents an affected mother and son in whom one of the two mutations in AS had occurred sporadically in the mother. The diagnosed of AS was based on associated abnormal physical features and on molecular genetic analysis. A C-to-G transversion at position 937 of the cDNA resulting in a proline-to-arginine substitution at codon 259 was found in the mother. In her second pregnancy, prenatal diagnosis by both restriction analysis and direct sequencing was undertaken and this showed that the female fetus had not inherited the mutation.

QS-21 and QS-7: purified saponin adjuvants

QS-21 and QS-7 are two adjuvant-active saponins that can be obtained in high purity from Quillaja saponaria Molina extracts. QS-21 is a highly characterized compound and is known to be a potent adjuvant for antibody and CD8+ CTL response to subunit antigens. Less is known about the activity and structure of the hydrophilic saponin QS-7. Hence, we have carried out a detailed structural and immunological characterization. As with QS-21, QS-7 was shown to be a 3,28-O-bisglycoside quillaic acid, with some differences being a higher degree of glycosylation and a considerably shorter fatty acyl unit in QS-7. These differences were correlated to a lower lytic activity against sheep red blood cells. Different doses of QS-7 were evaluated for stimulation of immune response to the antigen ovalbumin, given three times by subcutaneous route to C57BL/6 mice. QS-7 doses of 40 micrograms or higher were shown to induce a strong CD8+ CTL response reproducibly against E. G7-OVA targets (similar to that induced by a 5-10 micrograms dose of QS-21). QS-7 (at doses above 5 micrograms) was also shown to stimulate CTL against peptide 18 of HIV-1IIIB gp120 after three immunizations of Balb/c mice with recombinant gp120 and different doses of QS-7. These data suggest that a hydrophilic saponin with low lytic activity can stimulate MHC Class I CTL responses although a higher minimum dose may be required for some antigens.

Voltage-sensitive dyes for monitoring multineuronal activity in the intact central nervous system

Optical monitoring of activity provides new kinds of information about brain function. Two examples are discussed in this article. First, the spike activity of many individual neurons in small ganglia can be determined. Second, the spatiotemporal characteristics of coherent activity in the brain can be directly measured. This article discusses both general characteristics of optical measurements (sources of noise) as well as more methodological aspects related to voltage-sensitive dye measurements from the nervous system.

Sip1, a novel RS domain-containing protein essential for pre-mRNA splicing

Previous studies have shown that protein-protein interactions among splicing factors may play an important role in pre-mRNA splicing. We report here identification and functional characterization of a new splicing factor, Sip1 (SC35-interacting protein 1). Sip1 was initially identified by virtue of its interaction with SC35, a splicing factor of the SR family. Sip1 interacts with not only several SR proteins but also with U1-70K and U2AF65, proteins associated with 5' and 3' splice sites, respectively. The predicted Sip1 sequence contains an arginine-serine-rich (RS) domain but does not have any known RNA-binding motifs, indicating that it is not a member of the SR family. Sip1 also contains a region with weak sequence similarity to the Drosophila splicing regulator suppressor of white apricot (SWAP). An essential role for Sip1 in pre-mRNA splicing was suggested by the observation that anti-Sip1 antibodies depleted splicing activity from HeLa nuclear extract. Purified recombinant Sip1 protein, but not other RS domain-containing proteins such as SC35, ASF/SF2, and U2AF65, restored the splicing activity of the Sip1-immunodepleted extract. Addition of U2AF65 protein further enhanced the splicing reconstitution by the Sip1 protein. Deficiency in the formation of both A and B splicing complexes in the Sip1-depleted nuclear extract indicates an important role of Sip1 in spliceosome assembly. Together, these results demonstrate that Sip1 is a novel RS domain-containing protein required for pre-mRNA splicing and that the functional role of Sip1 in splicing is distinct from those of known RS domain-containing splicing factors.

Interaction of presenilins with the filamin family of actin-binding proteins

Mutations in presenilin genes PS1 and PS2 account for approximately 50% of early-onset familial Alzheimer's disease (FAD). The PS1 and PS2 genes encode highly homologous transmembrane proteins related to the Caenorhabditis elegans sel-12 and spe-4 gene products. A hydrophilic loop region facing the cytoplasmic compartment is likely to be functionally important because at least 14 mutations in FAD patients have been identified in this region. We report here that the loop regions of PS1 and PS2 interact with nonmuscle filamin (actin-binding protein 280, ABP280) and a structurally related protein (filamin homolog 1, Fh1). Overexpression of PS1 appears to modify the distribution of ABP280 and Fh1 proteins in cultured cells. A monoclonal antibody recognizing ABP280 and Fh1 binds to blood vessels, astrocytes, neurofibrillary tangles, neuropil threads, and dystrophic neurites in the AD brain. Detection of ABP280/Fh1 proteins in these structures suggests that these presenilin-interacting proteins may be involved in the development of AD and that interactions between presenilins and ABP280/Fh1 may be functionally significant. The ABP280 gene is located on the human X chromosome, whereas the newly identified Fh1 gene maps to human chromosome 3. These results provide a new basis for understanding the function of presenilin proteins and further implicate cytoskeletal elements in AD pathogenesis.

Molecular cloning of acid alpha-glucosidase cDNA of Japanese quail (Coturnix coturnix japonica) and the lack of its mRNA in acid maltase deficient quails

Acid alpha-glucosidase (GAA) hydrolyzes alpha-1, 4 and alpha-1, 6 glucosidic linkages of oligosaccharides and degrades glycogen in the lysosomes. The full-length GAA I cDNA, pQAM8, was isolated from a cDNA library derived from Japanese quail liver. The cDNA is 3569 base pairs long and has an open reading frame capable of coding 932 amino acids. The deduced amino acid sequence shares 52% identity with human GAA. Transfection of expression vector pETAM8 into COS-7 cells or acid maltase deficient (AMD) quail embryonic fibroblasts increased the level of GAA 20-50-fold. Compared to normal quail, the levels of GAA I mRNA were significantly reduced in the muscle, liver, heart, and brain of AMD quails, suggesting the GAA deficiency in AMD quail is due to a lack of GAA I mRNA. A second GAA II cDNA was identified after probing the cDNA library from the ovarian large follicles of quails with a PCR product derived from cultured quail skin fibroblasts. This clone having 3.1 kb insert, has GAA activity as well (3 to 10 fold increase). This cDNA, designated GAA II, predicted an 873 amino acid polypeptide showing 63% identity to human GAA and 51% identity to the GAA I. The RT-PCR analysis demonstrated that GAA II mRNAs were barely detectable in normal tissues, while they were enhanced to higher levels in AMD tissues. These results suggest that GAA II expression is up-regulated at the transcription levels, and quail GAA gene redundancy performs the same function of satisfying GAA demand at the two different phases represented by normal and AMD.

Early diabetes and abnormal postnatal pancreatic islet development in mice lacking Glut-2

Glut-2 is a low-affinity transporter present in the plasma membrane of pancreatic beta-cells, hepatocytes and intestine and kidney absorptive epithelial cells of mice. In beta-cells, Glut-2 has been proposed to be active in the control of glucose-stimulated insulin secretion (GSIS; ref. 2), and its expression is strongly reduced in glucose-unresponsive islets from different animal models of diabetes. However, recent investigations have yielded conflicting data on the possible role of Glut-2 in GSIS. Whereas some reports have supported a specific role for Glut-2 (refs 5,6), others have suggested that GSIS could proceed normally even in the presence of low or almost undetectable levels of this transporter. Here we show that homozygous, but not heterozygous, mice deficient in Glut-2 are hyperglycaemic and relatively hypo-insulinaemic and have elevated plasma levels of glucagon, free fatty acids and beta-hydroxybutyrate. In vivo, their glucose tolerance is abnormal. In vitro, beta-cells display loss of control of insulin gene expression by glucose and impaired GSIS with a loss of first phase but preserved second phase of secretion, while the secretory response to non-glucidic nutrients or to D-glyceraldehyde is normal. This is accompanied by alterations in the postnatal development of pancreatic islets, evidenced by an inversion of the alpha- to beta-cell ratio. Glut-2 is thus required to maintain normal glucose homeostasis and normal function and development of the endocrine pancreas. Its absence leads to symptoms characteristic of non-insulin-dependent diabetes mellitus.

Regulation of apolipoprotein A-I gene expression in Hep G2 cells depleted of Cu by cupruretic tetramine

Studies were designed to examine the regulation of apolipoprotein (apo) A-I gene expression in Cu-depleted Hep G2 cells. The cupruretic chelator N,N'-bis(2-aminoethyl)-1,3-propanediamine 4 HCl (2,3,2-tetramine or TETA) was used to maintain a 77% reduction in cellular Cu in Hep G2 cells. After two passages of TETA treatment, the relative abundance of apoA-I mRNA was elevated 52%. In TETA-treated cells, the rate of apoA-I mRNA decay measured by an actinomycin D chase study was accelerated 108%, and the synthesis of apoA-I mRNA determined by a nuclear runoff assay was enhanced 2.5-fold in TETA-treated cells. All of those changes could be reverted toward the control values with Cu supplementation for only 2 days. In transient transfection assays, a 26.7% increase in chloramphenicol O-acetyltransferase (CAT) activity for the reporter construct -256AI-CAT was observed in the treated cells. However, the ability of apoA-I regulatory protein 1 (ARP-1) to repress the CAT activity was not affected by the depressed Cu status. In addition, gel retardation experiments demonstrated that Cu depletion enhanced the binding of hepatocyte nuclear factor 4 (HNF-4) and other undefined nuclear factors to oligonucleotides containing site A, one of three regulatory sites of the apoA-I gene promoter. Moreover, the relative abundance of HNF-4 mRNA was increased 58% in the Cu-depleted cells. Thus the observed increase in apoA-I gene transcription may be mediated mostly by an elevated level of the regulatory factor, HNF-4. In summary, the present findings established the mechanism by which a depressed cellular Cu status can enhance apoA-I mRNA production and subsequently increase apoA-I synthesis.

Carbamoylation of brain glutamate receptors by a disulfiram metabolite

S-Methyl-N,N-diethylthiolcarbamate sulfoxide (DETC-MeSO), a metabolite of the drug disulfiram, is a selective carbamoylating agent for sulfhydryl groups. Treatment of glutamate receptors isolated from mouse brain with DETC-MeSO blocks glutamate binding. In vivo, carbamoylated glutathione, administered directly to mice or formed by reaction of DETC-MeSO with glutathione in the blood, also blocks brain glutamate receptors. Carbamoyl groups appear to be delivered to brain glutamate receptors or to liver aldehyde dehydrogenase in vivo by a novel glutathione-mediated mechanism. Seizures caused by the glutamate analogs N-methyl-D-aspartate and methionine sulfoximine, or by hyperbaric oxygen, are prevented by DETC-MeSO, indicating that carbamoylation of glutamate receptors gives an antagonist effect. These observations offer an explanation for some of the previously reported neurological effects of disulfiram, such as its ability to prevent O2-induced seizures. Furthermore, some of the physiology of the disulfiram-ethanol reaction, that could not be accounted for based on the known inhibition of aldehyde dehydrogenase alone, may be explained by disulfiram's effect on glutamate receptors.

Protein phosphorylation and taurine biosynthesis in vivo and in vitro

Taurine is known to be involved in many important physiological functions. Here we report that both in vivo and in vitro the taurine-synthesizing enzyme in the brain, namely cysteine sulfinic acid decarboxylase (CSAD), is activated when phosphorylated and inhibited when dephosphorylated. Furthermore, protein kinase C and protein phosphatase 2C have been identified as the enzymes responsible for phosphorylation and dephosphorylation of CSAD, respectively. In addition, the effect of neuronal depolarization on CSAD activity and 32P incorporation into CSAD in neuronal cultures is also included. A model to link neuronal excitation and CSAD activation by a Ca2+-dependent protein kinase is proposed.

Methyl-directed repair of mismatched small heterologous sequences in cell extracts from Escherichia coli

The methyl-directed DNA repair efficiency of a set of M13mp18 heteroduplexes containing 1-8 or 22 unpaired bases was determined by using an in vitro DNA mismatch repair assay. The unpaired bases of each heteroduplex residing at overlapping recognition sites of two restriction endonucleases allow independent assay of repair on either DNA strand. Our results showed that the repair of small nucleotide heterologies in Escherichia coli extracts was very similar to base-base mismatch repair, being strand-specific and highly biased to the unmethylated strand. The in vitro activity was also dependent on products of mutH, mutL, mutS, and uvrD loci and was equally efficient on nucleotide insertions and deletions. The repair levels of small heterologies were affected by base composition of the heterologies. However, the extent of repair of heteroduplexes containing small heterologous sequences was found to decrease with an increase in the number of unpaired bases. Heteroduplexes containing an extra nucleotide of 22 bases provoked very low level of methyl-directed repair.

Tyrosine kinase inhibition reduces i(f) in rabbit sinoatrial node myocytes

We studied pacemaker current (i(f)), the inward current activated by hyperpolarization in rabbit sinoatrial (SA) node myocytes, with the permeabilized-patch-clamp technique. The tyrosine kinase inhibitors genistein (50 microM) or herbimycin A (35 microM) reduced the amplitude of i(f) in response to step hyperpolarizations in the diastolic range of potentials. A two-step voltage-clamp protocol revealed that the reduction in i(f) is due to a decrease in maximal i(f) conductance. The observed effects are due to tyrosine kinase inhibition since an inactive analog of genistein did not reduce i(f). To further examine the mechanism of action, we added 2 mM chlorophenylthio cAMP (CPTcAMP, a membrane-permeant cAMP analog) to the bathing Tyrode, which increased i(f). Genistein still reduced i(f) in the presence of CPTcAMP. This suggests that the pathway mediating the actions of tyrosine kinase inhibition on i(f) is independent of cAMP- or protein-kinase-A-mediated phosphorylation.

TxA2-induced pulmonary artery contraction requires extracellular calcium

In order to examine the role of extracellular calcium in the pulmonary arterial vasoconstriction that is elicited by thromboxane A2 (TxA2), rabbits were sacrificed and the main trunk of the pulmonary artery removed. Contractile responses of the isolated vessel to the TxA2 mimetic, U46 619, were measured in a temperature controlled (37 degrees C) organ bath. Compared with control responses, U46 619 microM) contractions were nearly eliminated when 1 mM EGTA was added to the buffer. In the presence of normal extracellular calcium concentrations, antagonists of voltage sensitive calcium channels (e.g. verapamil and nifedipine) attenuated the U46 619-induced contractions. These voltage sensitive calcium channel blockers were more effective in eliminating contractile responses to high KCl concentrations (6) or 120 mM KCl). The inability of these calcium channel antagonists to completely eliminate U46 619 responses was confirmed in the anesthetized rabbit where both nifedipine and verapamil failed to block the increase in pulmonary arterial blood pressure resulting from intravenous U46 619 infusion. These results indicate that extracellular calcium is essential for U46 619-induced pulmonary vascular contraction, and that mechanisms in addition to voltage operated calcium channels participate in the movement of extracellular calcium through the plasma membrane.

Isolation and nucleotide sequence of canine glucose-6-phosphatase mRNA: identification of mutation in puppies with glycogen storage disease type Ia

Two Maltese puppies with massive hepatomegaly and failure to thrive had isolated deficient glucose-6-phosphatase (G-6-Pase) activity in liver and kidney and pathological findings compatible with GSD-Ia. To identify the mutation, we cloned G-6-Pase canine cDNA by RT-PCR with primers from the murine G-6-Pase gene sequence. The canine G-6-Pase cDNA is 2346 bp, with a 5' untranslated region of 87 bp, a coding region of 1071 bp, and a 3' untranslated region of 1185 bp. The difference between the canine and human sequences is in the 3' untranslated region. A greater than 90% amino acid sequence homology was seen with canine, human, murine, and rat G-6-Pase. G-6-Pase cDNA from affected and control puppies revealed complete homology except at nt position 450, which showed a guanine to cytosine (G to C) transversion resulting in substitution of a methionine by isoleucine at codon 121 (M121I) in all five clones studied. The loss of an NcoI restriction site on genomic DNA amplified with primers flanking the mutation allowed us to prove that affected puppies were homozygous for the mutation and parents were heterozygous carriers. The mutant G-6-Pase cDNA had 15 times less enzyme activity than wild-type cDNA following transient transfection. Northern blot analysis of puppies with GSD-Ia revealed increased G-6-Pase mRNA, compared to normal controls. Increased G-6-Pase mRNA was also seen in normal fasted puppies compared to littermates in the fed state, suggesting that the increased G-6-Pase mRNA is a physiologic response to fasting. This is the first report of a molecularly confirmed naturally occurring animal model of GSD-Ia. The establishment of a breeding colony of this dog strain will facilitate studies on the role of G-6-Pase gene in glucose homeostasis, in pathophysiology of disease, and development of novel therapeutic approaches such as gene therapy.

Induction of cross-reactive cytotoxic T-lymphocyte responses specific for HIV-1 gp120 using saponin adjuvant (QS-21) supplemented subunit vaccine formulations

The antigenic variation associated with Human Immunodeficiency Virus type-1 (HIV-1) envelope proteins could limit their utility in vaccines if the immune responses induced are specific for immunodominant variable epitopes. We evaluated the ability of experimental subunit vaccines, containing recombinant forms of the envelope glycoprotein (rgp120) from two HIV-1 variants, to induce immune responses capable of recognizing unrelated HIV-1 variants. A vaccine formulation based on HIV-1IIIB/LAI rgp120 and supplemented with saponin adjuvant (QS-21) induced neutralizing antibodies specific for the HIV-1IIIB/LAI variant. This antibody response was presumably specific for the variable principle neutralizing determinant (PND) of the third variable region of gp120, the V-3 region. This formulation induced cytotoxic T-lymphocytes (CTL) specific for the dominant V-3 epitope but also to an additional unidentified epitope outside of this region. The CTL specific for this second epitope also recognized gp120 from the HIV-1MN and HIV-1RF variants in a "cross-reactive" manner. A second vaccine formulation based on HIV-1MN rgp120 and QS-21 adjuvant induced neutralizing antibodies that were again variant-specific but also CTL that recognized all three HIV-1 variants in a cross-reactive manner. These data demonstrate that CTL capable of recognizing different HIV-1 variants, which are presumed to be specific for a conserved HIV-1 gp120 epitope, can be induced using subunit vaccines with the appropriate adjuvant while variant-specific antibody responses are produced. These findings support further evaluation of this vaccine format.

Percutaneous transluminal coronary angioplasty of the left anterior descending artery through a left main coronary artery of anomalous origin

While coronary arteries of anomalous origin are uncommon, some forms seem to be predisposed to atherosclerosis. Very few cases of percutaneous transluminal coronary angioplasty (PTCA) in anomalous arteries have been reported. We report a case of successful PTCA of the left anterior descending artery through an anomalous left main coronary artery originating from the right aortic sinus in a 65-year-old man with unstable angina. PTCA was performed using an 8 F 3.5 cm right Judkins guiding catheter to dilate a discrete 90% stenosis of the left anterior descending artery. After PTCA, the patient became symptom free. Using the proper guiding catheter, PTCA can be performed in coronary arteries of anomalous origin with excellent results.

HIV Rev-dependent binding of SF2/ASF to the Rev response element: possible role in Rev-mediated inhibition of HIV RNA splicing

Production of the structural and enzymatic proteins of type 1 human immunodeficiency virus (HIV-1) is controlled by the rev regulatory gene product. The 116-amino acid Rev protein acts by binding to the Rev response element (RRE), a complex RNA stem-loop structure located within the env gene of HIV. Rev exerts a series of posttranscriptional effects, including the inhibition of viral RNA splicing, the activation of nuclear export of incompletely spliced viral RNAs, and the enhancement of translation of RRE-containing RNAs. Our studies now demonstrate that at least one member of the SR family of splicing factors, SF2/ASF, specifically binds to a subregion of the RRE in vitro in a Rev-dependent manner. Furthermore, expression of high levels of SF2/ASF inhibits Rev function and impairs HIV replication in vivo. Both the in vitro binding of SF2/ASF to the Rev/RRE complex and the in vivo inhibition of Rev action by SF2/ASF are abrogated by mutation of the N-terminal RNA recognition motif but are not affected by mutation of the C-terminal arginine-serine-rich domain. These findings suggest that Rev inhibition of HIV splicing likely involves recruitment of the essential splicing factor SF2/ASF to the Rev/RRE complex. However, these inhibitory effects of Rev on viral RNA splicing are apparently overcome by augmenting the intracellular levels of SF2/ASF expression.

Neurobehavioral development of neonatal mice following blockade of VIP during the early embryonic period

Previous work has shown that blockade of VIP function in the early postimplantation embryo results in growth retardation and microcephaly. In the present work, the neurobehavioral development of neonatal mice was examined following treatment of dams with a VIP antagonist during this period. Inhibition of VIP functions during early embryogenesis impaired the performance of 5 of 10 developmental behaviors. These behaviors included developmental milestones (first appearance of ear twitch and eye opening) and complex motor behaviors (negative geotaxis, surface righting, and air righting). The retardation of neurobehavioral development produced by inhibition of VIP action indicates that this peptide is important to the progression of embryonic development.

Functional properties of p54, a novel SR protein active in constitutive and alternative splicing

The p54 protein was previously identified by its reactivity with an autoantiserum. We report here that p54 is a new member of the SR family of splicing factors, as judged from its structural, antigenic, and functional characteristics. Consistent with its identification as an SR protein, p54 can function as a constitutive splicing factor in complementing splicing-deficient HeLa cell S100 extract. However, p54 also shows properties distinct from those of other SR family members, p54 can directly interact with the 65-kDa subunit of U2 auxiliary factor (U2AF65), a protein associated with the 3' splice site. In addition, p54 interacts with other SR proteins but does not interact with the U1 small nuclear ribonucleoprotein U1-70K or the 35-kDa subunit of U2 auxiliary factor (U2AF35). This protein-protein interaction profile is different from those of prototypical SR proteins SC35 and ASF/SF2, both of which interact with U1-70K and U2AF35 but not with U2AF65. p54 promotes the use of the distal 5' splice site in E1A pre-mRNA alternative splicing, while the same site is suppressed by ASF/SF2 and SC35. These findings and the differential tissue distribution of p54 suggest that this novel SR protein may participate in regulation of alternative splicing in a tissue- and substrate-dependent manner.

Effect of feedback from peripheral movements on neuron activity in the aplysia abdominal ganglion

We have made reasonably comprehensive measurements of action potential activity in the Aplysia californica abdominal ganglion to determine the amount of feedback the central nervous system (CNS) receives from a movement which it initiates. Voltage-sensitive dye measurements of action potential activity of cells in the ganglion were made during the gill-withdrawal reflex elicited by siphon stimulation. We compared recordings in two situations which differed dramatically in the amount the gill moved. In the control sea water, the gill withdrawal was normal; in low-Ca2+, high-Mg2+ sea water, the gill movement was blocked. Both the timing and the number of spikes of the individual neurons were similar in the two situations. Histograms of the summed spike activity versus time and histograms of the number of active neurons versus time in the two conditions were also similar. Finally, two numerical measures of trial-to-trial differences, a paired t-test and a measure we named fractional similarity, did not indicate larger differences between two trials in the different sea waters than two trials in the same sea water. Feedback from sensory neurons activated by the gill movement itself does not make a large contribution to the spike activity in the abdominal ganglion. Apparently the Aplysia CNS issues the command for the withdrawal and does not make adjustments for the magnitude of the actual withdrawal. It may not even receive the information necessary for such adjustments to be made. A second motivation for these experiments was to test whether removing the feedback might simplify the neuronal activity that occurs during the gill-withdrawal reflex. This did not occur.

Copper deficiency increases total protein and apolipoprotein A-I synthesis in the rat small intestine

This study was designed to determine whether an enhanced intestinal synthesis of apolipoprotein (apo) A-I is associated with the hyperapolipoproteinemia observed in copper-deficient rats. Male weanling Sprague-Dawley rats were assigned to two dietary treatments, Cu deficient (0.6 ppm Cu) and Cu adequate (6.0 ppm Cu) for 6 weeks. In vivo studies were then performed after rats were injected with a flooding dose of 150 microM [3H]phenylalanine (PHE, 50 microCi/ml/100 g body wt). Three rats from each treatment were sacrificed at 5, 10, 15, 30, and 60 min postinjection. The small intestine was rapidly rinsed and frozen in liquid N2. In vitro studies were performed by labeling freshly isolated 6-cm segments from duodenum, jejunum and ileum with [3H]PHE (33 microCi/ml, 49.7 Cl/mmol) in PHE-free minimum essential medium for 7 and 14 min. In vivo and in vitro intestinal samples were sonicated, solubilized in 1% Triton X-100, and centrifuged to provide the detergent soluble fraction for the isolation of nascent apo A-I and total protein. Radioactivities associated with nascent apo A-I isolated by immunoprecipitation and SDS-PAGE, and with total protein precipitated by trichloroacetic acid, were measured to determine the influence of Cu deficiency on nascent apo A-I and total protein synthesis. In the Cu-deficient small intestine, the synthesis of total protein was measured only in the duodenum and was enhanced after 1 hr for the in vivo studies. Moreover, total protein synthesis was enhanced at both 7 and 14 min of the in vitro studies for all three small intestinal segments of the Cu-deficient rats. Apo A-I synthesis was measured only at the jejunum and was also enhanced by Cu deficiency in the in vitro studies. Thus, an increase in intestinal apo A-I synthesis may contribute to the elevated plasma apo A-I level in Cu-deficient rats.