Evidence of Na Current Contribution to the Transient Outward Current in Cardiac Ventricular Myocytes

BACKGROUND: To study the transient outward current (I(to)) investigators often use sodium-free external solution to minimize the possible contamination of I(to) by sodium current. Removal of extracellular sodium creates reversal of sodium gradient and thus possibly contributing to I(to) mainly at positive potentials. METHODS AND RESULTS: To address this issue, whole-cell I(to) was recorded in sodium-free choline chloride and cobalt solutions, from rat ventricular myocytes known to exhibit a prominent I(to). Depolarizing pulse to 40 mV from -100 mV holding potential every 10 seconds elicited a fast activating and time-dependent inactivating components. The activation of I(to) was fast and complete within 10 ms at 40 mV, and the decay was rapid over the first 100 ms of the pulse and slower thereafter. External superfusion of the cell with 50 µM tetrodotoxin reversibly reduced I(to) amplitude by 25% from 1.47 +/- 0.2 to 1.1 +/- 0.3 nA (P <.04, n = 9). When sea anemone toxin (ATXII), known to selectively enhanced I(Na) by causing a delay in the inactivation gate, is applied to the cell, I(to) amplitude increased in a time- and dose-dependent manner (EC(50) =.86.4 nM). ATXII (100 nM) dramatically increased I(to) amplitude at all voltages between -20 and 60 mV (from 1.51 +/- 0.4 to 3.35 +/- 0.8 nA at 40 mV, P <.003, n = 12). Superfusion of cells with 5 mM 4-AP resulted in 82% reduction in I(to) amplitude at 40 mV (from 1.95 +/- 0.5 to 0.37 +/- 0.2 nA, P <.02, n = 8). Addition of ATXII to 4-AP containing solution increased peak I(to) by 965% (from 0.37+/-0.2 to 3.95 +/- 0.9, n = 8, P <.0003). However, in 11 other cells, addition of tetrodotoxin (50 µM) to the ATXII-containing solution blocked ATXII-induced outward current (from 3.51 +/- 0.64 nA to 1.60 +/- 0.17 nA, P <.05). The conductance (G(Ito)) was calculated by dividing peak I(to) by (Vm-E(K)), with an E(K) of -75 mV. G(Ito) was increased at all voltages (greater than -40 mV). Normalized G(Ito) was fitted by Boltzmann equation and ATXII did not significantly modify V(0.5) and k (from -20.5 +/- 3.9 to -17.0 +/- 3.5 mV for V(0.5), and 12.2 +/- 2.6 to 13.4 +/- 2.1 mV for k, n = 4). Also, atropine (1 µM) did not have any significant effect on I(to) (from 1.92 +/- 0.15 nA to 1.85 +/- 0.25 nA, n = 5). CONCLUSIONS: The results showed that, in sodium-free external solution I(to) is tetrodotoxin but not atropine sensitive. ATXII-induced I(to) increase is 4-aminopyridine insensitive but tetrodotoxin sensitive. These data suggest that outward Na current due to reversal of Na gradient in the absence of external Na contributes to I(to). Caution must be taken when studying kinetics and pharmacology of I(to) in external sodium-free solutions.

Structural basis for IL-4 receptor phosphopeptide recognition by the IRS-1 PTB domain

We present the NMR structure of the PTB domain of insulin receptor substrate-1 (IRS-1) complexed to a tyrosine-phosphorylated peptide derived from the IL-4 receptor. Despite the lack of sequence homology and different binding specificity, the overall fold of the protein is similar to that of the Shc PTB domain and closely resembles that of PH domains. However, the PTB domain of IRS-1 is smaller than that of Shc (110 versus 170 residues) and binds to phosphopeptides in a distinct manner. We explain the phosphopeptide binding specificity based on the structure of the complex and results of site-directed mutagenesis experiments.

[Comparison of human papilloma virus-DNA in condyloma acuminatum, cervical cancer and the female genital tract]

OBJECTIVE

To examine human papilloma virus (HPV) infection rate and types in several lesions of the genital tract and to observe the relation between HPV and host cells for differential handling of cases and for early diagnosis.

METHODS

Tissues from 89 cases of condyloma acuminata, 76 cases of cervical cancer and swabs from 198 cases of normal vaginal were analysed by polymerase chain reaction for HPV infective rate. Main HPV types were compared and Southern blot was used to compare the physical pattern of HPV in condyloma acuminata and cervical cancer.

RESULTS

The positive rates of HPV-DNA in condyloma acuminata and cervical cancer were respectively 98.9% and 94.7%. The primary types of the former were HPV 6, 11 and of the latter mainly 16 and 18. The latent infective rates in normal vagina was 37.4%, among which, HPV 6, 11, 16, 18 consisted of only 21.6%. HPV11-DNA in condyloma acuminata existed mainly in episodic form. Most of HPV16-DNA in cervical cancer integrates into the host cells with variation.

CONCLUSIONS

The different types of HPV are related to particular morphology and characteristics of lesions. The relation of HPV-DNA to host cell and can offer some reference for the determination of the character of the lesion, and it may be award of malignant transformation.

Mutations in human CD4 impair the functional interaction with different human and mouse class II isotypes and alleles

The structure-function of the CD4-class II MHC interaction was investigated. Two functional assays were used to assess the responses of the 3DT52.5.8 murine T cell hybridoma expressing human CD4 (h-CD4) or murine CD4 (m-CD4). First, we determined the responses of the CD4+ and CD4-effector cells toward DAP-3 cells co-expressing the cognate alloantigen H-2Dd together with several human (DRw52b, DR4-Dw4, DR2A, and DPw2) and murine (I-Ab, I-Ak, IA alpha b I-A beta k and I-Ek) class II alleles and isotypes. We found that h-CD4 and m-CD4 strongly enhance the T cell response to H-2Dd, demonstrating that interspecies CD4/class II interactions occur efficiently. Furthermore, mutations in h-CD4 at positions 19, 89, and 165 markedly reduced the interaction with both human class II and mouse class II, indicating that the structural features of this cross-species interaction are strongly conserved. This was further supported by the finding that a h-CD4 deletion mutant (deletion F43-S49) interacted with both human and murine class II. Moreover, as 3DT cells express the responsive V beta element for the bacterial superantigen staphylococcal enterotoxin B, a co-receptor assay was conducted. DAP-3 cells expressing only class II molecules were used as APCs to present staphylococcal enterotoxin B to h-CD4+ and m-CD4+ T cells. h-CD4 and m-CD4 were able to enhance the T cell response to staphylococcal enterotoxin B, further demonstrating the conservation of the CD4-class II MHC interaction.

Mutations in human CD4 impair the functional interaction with different human and mouse class II isotypes and alleles

The structure-function of the CD4-class II MHC interaction was investigated. Two functional assays were used to assess the responses of the 3DT52.5.8 murine T cell hybridoma expressing human CD4 (h-CD4) or murine CD4 (m-CD4). First, we determined the responses of the CD4+ and CD4-effector cells toward DAP-3 cells co-expressing the cognate alloantigen H-2Dd together with several human (DRw52b, DR4-Dw4, DR2A, and DPw2) and murine (I-Ab, I-Ak, IA alpha b I-A beta k and I-Ek) class II alleles and isotypes. We found that h-CD4 and m-CD4 strongly enhance the T cell response to H-2Dd, demonstrating that interspecies CD4/class II interactions occur efficiently. Furthermore, mutations in h-CD4 at positions 19, 89, and 165 markedly reduced the interaction with both human class II and mouse class II, indicating that the structural features of this cross-species interaction are strongly conserved. This was further supported by the finding that a h-CD4 deletion mutant (deletion F43-S49) interacted with both human and murine class II. Moreover, as 3DT cells express the responsive V beta element for the bacterial superantigen staphylococcal enterotoxin B, a co-receptor assay was conducted. DAP-3 cells expressing only class II molecules were used as APCs to present staphylococcal enterotoxin B to h-CD4+ and m-CD4+ T cells. h-CD4 and m-CD4 were able to enhance the T cell response to staphylococcal enterotoxin B, further demonstrating the conservation of the CD4-class II MHC interaction.

Reemergence of the fetal pattern of L-type calcium channel gene expression in non infarcted myocardium during left ventricular remodeling

The cardiac L-type voltage-dependent calcium channel (VDCC) is a critical component of cardiac action potential and excitation-contraction coupling. The objective of the present study was to examine the changes in expression in Motif IV, an alternatively spliced region of the alpha-1 subunit of the VDCC channel in postmyocardial infarction (MI) remodeled rat left ventricle. RNase protection assay was used to determine alteration in isoform expression in the noninfarcted hypertrophied ventricular myocardium 21 days post myocardial infarction. Our study demonstrates that cardiac hypertrophy is associated with significant increase in the mRNA level of the fetal isoform, with the reversion of fetal:adult isoform ratio to the fetal phenotype. Changes in isoform expression in the post-MI remodeled ventricle, not previously reported, is a pertinent genetic marker of cardiac hypertrophy.

[Changes of lung function in ex-smokers]

Lung function in 31 ex-smokers, 17 with six to eight and 14 with 11 to 15 years of cigarette smoking, and pair-matched controls were studied. Results showed smoking could cause prolongation of mean through time and partial mean through time in forced expiratory volume scheme, which increased with length of smoking, and multiple abnormal in lung function tests. Lung function could improve apparently after the cease of smoking. It suggested quitting of smoking could prevent lung function from further damage, or reverse the damaged lung function.

[Effects of hypoxia on the phenotype of porcine pulmonary arterial smooth muscle cells in vitro]

The effects of hypoxia on phenotype modulation of pulmonary artery smooth muscle cells (PASMC) was observed using cell culture and morphometry analysis. The results showed that the number of diploid cells and alpha-sm-actin of the hypoxic endothelial cell condition medium group (HECCM) was lower and the myofibrils were even less than that of the normal endothelial cell condition medium group (NECCM). On the contrary, the volume density of rough endothelial reticulum (RER) and mitochondria of the HECCM group were higher than that of the NECCM group. However, under hypoxic condition for 24 hours, the phenotype of cultured PASMCs remained unchanged. It suggests that the HECCM can induce phenotype modulation of PASMCs, may be mediated by the pulmonary artery endothelial cells (PAECs) which can secrete some cytokines affecting the PASMCs.

Erectile response to topical, intraurethral and intracorporal pharmacotherapy in a rat model of spinal cord injury

In order to compare the erectile response to topical, intraurethral and intracorporal administration of vasoactive substances in neurologically intact and spinal cord injured (SCI) rats, a standard rat model of SCI using impact trauma at the level of T10 was employed, comparing the tumescence of 24 SCI and 25 control rats. Four weeks after SCI, the effect of vasoactive substances on erectile function was evaluated. Under ketamine anesthesia, the penis was exposed and intracorporal pressure (ICP) was monitored using saline infusion cavernosometry through a 24-gauge catheter inserted into one corpus cavernosum. Changes in ICP were recorded in response to the topical and intraurethral (IU) application of minoxidil (0.1 ml, 2% solution) and 2% nitroglycerin (NTG) ointment (0.1 gm), as well as the intracorporal (IC) administration of papaverine (0.0001-0.10 mg/kg). Results indicated that the mean baseline ICP was 8 +/- 5 mmHg for SCI and 9 +/- 4 mmHg for control rats. No response to topical therapy onto the undegloved penis was noted in either SCI or control rats. IU application of minoxidil to the degloved phallus developed ICP greater than that achieved with topical minoxidil; the topical application of NTG was less effective. In SCI rats, IC papaverine injection achieved an ICP of 56.9 +/- 24.3 mmHg, whereas papaverine in control rats generated an ICP of 43.5 +/- 38.8 mmHg. A greater increase in ICP at lower doses of each agent occurred in SCI than in control rats. We conclude that only the degloved phallus responded to topical vasoactive pharmacotherapy. Although both topical and IU applications of NTG and minoxidil increase ICP, tumescence was significantly less than that achieved with IC injection of papaverine. The IU application of minoxidil demonstrated significantly greater activity than other topical therapies. SCI rats displayed a supersensitive response to all modes of pharmacologic erectile therapy.

[Interleukin-2 gene cloning and expression in S. cerevisiae]

Mature human Interleukin-2 gene was amplified from IL-2 cDNA by PCR methods. The PCR product was cloned into pUC12 plasmid at Sma I site, then precisely engineered into an intermidiate vector pSK43SB which were digested with Hind III, mung bean nuclease, and Sal I. Added BamH I linker to Cla I site of pSK43SB-IL2 to produce one more BamH I site, then digested pSK43DB-IL2 with restriction enzyme BamH I, the BamH I fragment with an alpha-factor leading sequence, IL2 gene and cycl terminater were produced. It was then cloned into a typical high efficiency episomal expression vector YEpHc8. Human IL-2 protein was purified from supernatant secreted by yeast transformants of YEpHc8-IL2 leading by alpha-factor promoter with IL-2 right translational reading frame and accurate cleavage site. High level expression of IL-2 with highly activity has been purified. A sugar specific silver staining method and 3H sugar labelling experiment has shown the detection of carbohydrate component.

Identification of an upstream region that controls the transcription of the human autocrine motility factor receptor

We have isolated from a human placenta cosmid library a 0.7 kb genomic clone that contains the 5' terminal portion of the autocrine motility factor receptor (hAMFR) coding region. Chloramphenicol Acetyl Transferase (CAT) reporter gene assays have identified this region as the promoter of the hAMFR gene. A single transcription initiation site (+1) has been mapped to 129 bp upstream of the ATG start codon by primer extension. DNA sequence analysis and CAT assay revealed a TATA element at the position -485/-468 which was able to conduct only a marginal transcription (less than 5% of the total activity). The majority of the hAMFR promoter's activity is contributed by a transcription initiator (Inr) element overlapping the initiation site (+1) which independently controls the transcription of the hAMFR gene. Gel mobility shift assays showed that DNA-binding proteins in HeLa cells nuclear extract can bind specifically to both promoter's elements. DNA-binding proteins were found to be differentially expressed by sparse and dense cultured normal fibroblasts. The nuclear-binding protein expressed by sparse NIH-3T3 cells induced a DNA mobility shift similarly to the nuclear protein of HeLa cells, while a different DNA-protein complex size was observed with nuclear proteins extracted from dense cultured NIH-3T3 cells. Also CAT-reporter gene analysis revealed a significant lower activity in dense NIH-3T3 cells as compared with the sparse-cultured counterparts. These results help to explain the previously observed cell-cell contact regulation of AMFR expression in normal cells and its consecutive expression in tumor cells.

Heritability and heteromorphic distributions of AluI chromosome banding variants in twins

The heritability and heteromorphic appearance of chromosomal banding patterns induced through in situ digestion with the restriction enzyme AluI were studied by analyzing the chromosomes of 25 monozygotic and 25 dizygotic twin pairs selected at random from a juvenile twin registry. A total of 19 AluI banding variants were found to be heteromorphic, with the pericentromeric region of chromosome 3 and the satellites of chromosome 22 being most and least heteromorphic, respectively. As expected, the correlations of the semi-quantitative scores for each of the chromosomal variants were significantly higher between MZ twin pairs (ranging from 0.48 to 0.95) than DZ twin pairs (ranging from -0.02 to 0.69), suggesting that genetic factors play an important role in their appearance. This finding was confirmed in a model fitting analysis in which the heritabilities of the AluI-induced chromosome variants were found to range from 70 to 96% for 12/13 heteromorphisms studied. These consistent findings are significant in that these variants may be useful for family studies in clinical genetics.

Molecular characterization of two proximal deletion breakpoint regions in both Prader-Willi and Angelman syndrome patients

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are distinct mental retardation syndromes caused by paternal and maternal deficiencies, respectively, in chromosome 15q11-q13. Approximately 70% of these patients have a large deletion of approximately 4 Mb extending from D15S9 (ML34) through D15S12 (IR10). To further characterize the deletion breakpoints proximal to D15S9, three new polymorphic microsatellite markers were developed that showed observed heterozygosities of 60%-87%. D15S541 and D15S542 were isolated from YAC A124A3 containing the D15S18 (IR39) locus. D15S543 was isolated from a cosmid cloned from the proximal right end of YAC 254B5 containing the D15S9 (ML34) locus. Gene-centromere mapping of these markers, using a panel of ovarian teratomas of known meiotic origin, extended the genetic map of chromosome 15 by 2-3 cM toward the centromere. Analysis of the more proximal S541/S542 markers on 53 Prader-Willi and 33 Angelman deletion patients indicated two classes of patients: 44% (35/80) of the informative patients were deleted for these markers (class I), while 56% (45/80) were not deleted (class II), with no difference between PWS and AS. In contrast, D15S543 was deleted in all informative patients (13/48) or showed the presence of a single allele (in 35/48 patients), suggesting that this marker is deleted in the majority of PWS and AS cases. These results confirm the presence of two common proximal deletion breakpoint regions in both Prader-Willi and Angelman syndromes and are consistent with the same deletion mechanism being responsible for paternal and maternal deletions. One breakpoint region lies between D15S541/S542 and D15S543, with an additional breakpoint region being proximal to D15S541/S542.

Phospholipase A2 engineering. Probing the structural and functional roles of N-terminal residues with site-directed mutagenesis, X-ray, and NMR

The N-terminal residues of phospholipase A2 (PLA2) are believed to be involved in the hydrogen-bonding network, the interfacial binding site, or the hydrophobic channel. Site-directed mutants of bovine pancreatic PLA2 with substitutions at positions 2, 3, 4, 5, 6, and 9 were constructed to test the roles of these residues in the structure and function of PLA2. Nonconservative mutations of Phe-5 and Ile-9, which are located inside the hydrophobic channel, led to significant perturbations in the conformation and conformational stability. Kinetic studies also indicated that mutations at Ile-9 and Phe-5 caused significant decreases in the rate of hydrolysis toward micellar and vesicle substrates. Scooting mode kinetic analysis showed that the binding step of the mutant enzymes to the DC14PM (1,2-dimyristoyl-sn-glycero-3-phosphomethanol) vesicle interface is not significantly affected and that the perturbations in catalysis occur mainly in kcat at the interface. The results taken together suggest that the residues Ile-9 and Phe-5 are important for both structure and catalysis. The mutant W3A (Trp-3 to Ala) also showed decreased rates of hydrolysis but to a lesser extent than Ile-9 and Phe-5 mutants. In addition, the binding affinity of W3A to the surface of the vesicles (i.e., the E to E* step) has been perturbed to the extent that hopping between anionic vesicles has been observed. On the other hand, the mutants of Gln-4 and Asn-6, which are located at or near the surface, displayed structural and kinetic properties similar to those of the wild-type PLA2 with the exception of the highly hydrophilic lysine mutant. The X-ray structure of the Q4E mutant indicates that the overall structure, the catalytic triad, and the link between residue 4 and Asp-99 via hydrogen bonding through Ala-1 and the structural water remain the same as in the WT. Substitutions for Leu at position 2 showed an acyl chain length discrimination toward different substrates, which may reflect the contacting position(s) of the substrate acyl chain with Leu-2.

Arachidonic acid as a possible negative feedback inhibitor of nicotinic acetylcholine receptors on neurons

Neuronal acetylcholine receptors, being highly permeable to calcium, are likely to regulate calcium-dependent events in neurons. Arachidonic acid is a membrane-permeant second messenger that can be released from membrane phospholipids by phospholipases in a calcium-dependent manner. We show here that activation of neuronal acetylcholine receptors triggers release of 3H-arachidonic acid in a calcium-dependent manner from neurons preloaded with the fatty acid. Moreover, low concentrations of arachidonic acid reversibly inhibit the receptors and act most efficiently on receptors likely to have the highest permeability to calcium, namely receptors containing alpha 7 subunits. Low concentrations of arachidonic acid also reversibly inhibit alpha 7-containing receptors expressed in Xenopus oocytes following injection of alpha 7 cRNA. The oocyte results indicate following injection of alpha 7 cRNA. The oocyte results indicate that the inhibition is a feature of the receptors rather than a consequence of neuron-specific machinery. The inhibition is not mediated by specific metabolites of arachidonic acid because the effects can be mimicked by other fatty acids; their effectiveness correlates with their content of double bonds. In contrast to arachidonic effects on calcium currents, inhibition of neuronal nicotinic receptors by the fatty acid cannot be prevented by blocking production of free radicals or by inhibiting protein kinase C. An alternative mechanism is that arachidonic acid binds directly to the receptors or perturbs the local environment in such a manner as to constrain receptor function.(ABSTRACT TRUNCATED AT 250 WORDS)

Niemann-Pick disease type C presenting as neonatal hepatitis: report of one case

A three-month old Chinese male infant was a victim of neonatal hepatitis presenting with prolonged jaundice, poor body weight gain, progressive hepatosplenomegaly and extremely elevated serum alpha-fetoprotein level. Niemann-Pick disease (NPD) type C was confirmed by autopsy, which revealed sphingolmyelin deposition in multiple visceral organs, and normal sphingomyelinase activity in liver. This is the first case of NPD type C in Taiwan. In idiopathic neonatal hepatitis with hepatosplenomegaly here, NPD type C must be taken into consideration.

Autonomic dysreflexia in a rat model spinal cord injury and the effect of pharmacologic agents

The object of this study was to develop a spinal cord injury (SCI) rat model for autonomic dysreflexia (AD), assessing the effect of alpha-adrenergic and calcium channel blockade and to determine the relationship of detrusor-external sphincter dyssynergia (DESD) to the development of AD. A laminectomy was performed in male rats at the T4 or T10 level and a controlled 50 g cm blunt SCI was induced using an impounder. Four weeks after injury, changes in arterial blood pressure and heart rate were monitored while simultaneous cystometry (CMG) and pelvic floor electromography (EMG) were performed in vivo in sham (control) and spinal cord injured rats. The effects of terazosin (0.1 mg/kg), diltiazem (0.5 mg/kg), and oxybutynin chloride (0.1 mg/kg) on hemodynamic changes were assessed independently. Both T4 and T10 SCI rat displayed evidence of DESD (enhanced pelvic floor EMG activity at cystometric capacity) while control rats did not. Only T4 injured rats exhibited evidence of AD, with mean blood pressure elevations from 82.9 +/- 13.6 to 93.9 +/- 11.3 mm Hg (P < 0.01) and a mean heart rate decrease from 332.2 +/- 56.5 to 311.1 +/- 54.5 beats/min (P = 0.02) at cystometric capacity. The intravenous administration of terazosin or diltiazem abolished the AD response during CMG. The administration of oxybutynin exhibited the ability to increase bladder capacity and improve compliance in all 3 groups but did not blunt AD. The rat model of SCI effectively reproduced hemodynamic changes consistent with the AD complex in T4 level SCI but not T10 level SCI animals, despite incomplete lesions. Blockade with either an alpha-1 or a calcium channel antagonist effectively ablated the AD response to bladder distention. Anticholinergic agents had no effect on AD. DESD frequently accompanies autonomic dysreflexia, although the development of AD is not a prerequisite for DESD.

A small, high-copy-number vector suitable for both in vitro and in vivo gene expression

A 2433-bp, high-copy-number expression vector, pUK, was constructed from pUC19 and pKK223-3. The genes encoding chicken adenylate kinase (AK) and phospholipase A2, cloned into pUK, were highly expressed in vitro using the coupled transcription/translation system of Zubay. High-level in vivo expression in Escherichia coli was also demonstrated for the AK gene cloned in this vector. The multiple cloning site (MCS) of pKK223-3 was preserved in pUK. In addition, three more sites in the MCS sequence, AccI, BamHI and SalI, were made unique for the convenience of cloning.

Rise of blood pressure with age. New evidence of population differences

Epstein and Eckoff in 1967 devised a scheme to summarize population differences in the rise of mean values of systolic blood pressure by age in accordance with their slopes and levels. For the first time, the validity of this scheme can be examined with data from a single study, INTERSALT. This study included 52 populations in 32 countries. On the basis of these data, collected in an exceptionally well-standardized mode under a common protocol, the diversity of populations in the slopes of age differences in median values of systolic blood pressure has been strongly reconfirmed. Populations with no increase in median systolic blood pressure were again observed and remained exceptional. The analyses of these data also indicate a positive relation between the slope of rising systolic blood pressure with age and urinary sodium, urinary sodium-potassium ratio, and reported alcohol consumption as well as a negative association between urinary potassium excretion and blood pressure slope. The present analyses therefore add to the previous knowledge and results published by the INTERSALT investigators in the following three respects: (1) they relate INTERSALT results to the postulated biological gradient of variation among populations as presented by Epstein and Eckoff, including explanatory variables; (2) they demonstrate strong correlation between ranks of median blood pressure at 40 to 49 years and values at 20 to 29 years; and (3) they therefore support the original Epstein and Eckoff concept of population variation, link this with blood pressure risk factors, and call attention to the large degree of population differences already evident among populations at 20 to 29 years of age.

Expression of the BnmNAP subfamily of napin genes coincides with the induction of Brassica microspore embryogenesis

Brassica napus cv. Topas microspores can be diverted from pollen development toward haploid embryo formation in culture by subjecting them to a heat stress treatment. We show that this switch in developmental pathways is accompanied by the induction of high levels of napin seed storage protein gene expression. Changes in the plant growth or microspore culture conditions were not by themselves sufficient to induce napin gene expression. Specific members of the napin multigene family were cloned from a cDNA library prepared from microspores that had been induced to undergo embryogenesis. The majority of napin clones represented three members (BnmNAP2, BnmNAP3 and BnmNAP4) that, along with a previously isolated napin genomic clone (BngNAP1), constitute the highly conserved BnmNAP subfamily of napin genes. Both RNA gel blot analysis, using a subfamily-specific probe, and histochemical analysis of transgenic plants expressing a BngNAP1 promoter-beta-glucuronidase gene fusion demonstrated that the BnmNAP subfamily is expressed in embryogenic microspores as well as during subsequent stages of microsporic embryo development.

Reorganization and condensation of chromatin in mitotic prophase nuclei of Allium cepa

This paper studies the process and features of chromosome construction in mitotic prophase cells of Allium cepa. The results showed that a prominent reorganization of chromatin occurred during G2--early prophase. The 250-400 nm thick compact chromatin threads in G2 nuclei began to disorganize into about 30, 100 and 220 nm chromatin fibres which constituted the loosely organized chromosome outlines in early prophase before chromosome condensation. In middle prophase, chromosome condensation was characterized by the formation of many condensed regions (aggregates of chromatin), which increased in size (1-1.5 microns) when prophase proceeded. Meanwhile, the chromatin threads that constituted and connected the condensed regions became increasingly thicker (120-250 nm). In late prophase adjacent condensed regions fused to form cylinder-shaped chromosomes. Based on these observations, we come to the conclusion that the construction of prophase chromosomes is a two-step process, that is, the reorganization and condensation of chromatin. In addition, we report the study of silver-stained, DNA- and histone-depleted prophase chromosomes, describe morphological features of the non-histone protein (NHP) residue in early, middle and late prophase chromosomes, and discuss the roles of NHPs in chromosome construction.

[Amplification, cloning and sequencing of beta nerve growth factor gene in the Chinese population]

Genomic DNA was extracted from white blood cells. Using the genomic DNA as template, the gene encoding nerve growth factor (beta-NGF) in the Chinese population was amplified using polymerase chain reaction (PCR). The beta-NGF gene obtained by PCR was then cloned into plasmid pUC 12 which was digested with SmaI. After transformation, screening and identification, 8 clones containing the beta-NGF gene were analyzed. Nucleotide sequence of the NGF was determined by dideoxy-nucleotide chain-termination method. The sequencing result showed that there are 6 differences between the beta-NGF sequence of the Chinese population and previous reported beta-NGF sequence.

Mental retardation and Ullrich-Turner syndrome in cases with 45,X/46X,+mar: additional support for the loss of the X-inactivation center hypothesis

Four cases having mosaicism for a small marker or ring [45,X/46,X,+mar or 45,X/46,X,+r] chromosome were ascertained following cytogenetic studies requested because of minor anomalies (cases 1, 3, and 4) and/or short stature (cases 2 and 4). While all 4 cases had traits typical of Ullrich-Turner syndrome (UTS), cases 1, 3, and 4 had manifestations not usually present in UTS, including unusual facial appearance, mental retardation/developmental delay (MR/DD) (cases 3 and 4), and syndactylies (case 1). The facial appearances of cases 1 and 3 were similar yet distinct from that of case 4. Using fluorescence in situ hybridization (FISH), each of the markers in these 4 cases was identified as having been derived from an X chromosome. The level of mosaicism for the mar/r(X) cell line in these cases varied from 70% (case 1) to 16% (case 4) but was not apparently correlated with the presence of MR/DD. Replication studies demonstrated a probable early replication pattern for the mar/r(X) in cases 1, 3, and 4, while the marker in case 2 was apparently late replicating. To date, 41 individuals having mosaicism for a small mar/r(X) chromosome have been described. Interestingly, most of the 14 individuals having a presumedly active mar/r(X) demonstrated clinical findings atypical of UTS, including abnormal facial changes (11) and MR/DD (13). MR was noted most frequently in those cases having at least 50% mosaicism for the marker or ring. In contrast, atypical UTS facial appearance or MR/DD was not noted in 14 of the 16 cases with UTS who carried a probable late replicating marker or ring. In conclusion, although the phenotype of 45,X/46,X,mar/r(X) individuals appears to be influenced by the genetic content and degree of mosaicism for the mar/r(X), the most significant factor associated with MR/DD appears to be the activity status of the mar/r(X) chromosome. Thus, our 4 cases provide further support for the hypothesis that a lack of inactivation of a small mar/r(X) chromosome may be a factor leading to the MR and other phenotypic abnormalities seen in this subset of individuals having atypical UTS.

High level expression in Escherichia coli and characterization of the EF-hand calcium-binding protein caltractin

Caltractin is a member of the calmodulin superfamily of Ca(2+)-binding proteins that was originally cloned at the DNA level from the unicellular green alga Chlamydomonas reinhardtii. Human and mouse homologs to algal caltractin have been recently characterized. In the studies reported here, recombinant Chlamydomonas caltractin was expressed at high levels in Escherichia coli and purified to homogeneity. The use of the ompT-host BL21 proved critical for obtaining high yields of homogeneous full-length protein. Growth and purification protocols were optimized to allow reproducible and efficient production of tens of milligrams of pure protein from 1-liter cultures. Caltractin has a distinct UV spectrum which is largely dominated by the fine structure due to the 9 Phe residues. Unlike other members of the same protein family, the UV and the CD spectra do not change upon addition of Ca2+ to the apoprotein. However, the 1H NMR spectrum shows distinct changes upon Ca2+ binding, which are indicative of structural and/or dynamic changes largely reminiscent of other members of the calmodulin superfamily. Ca2+ binding measurements demonstrated the binding of four Ca2+ ions to caltractin with two higher affinity (Kd = 1.2 x 10(-6) M) and two lower affinity (Kd = 1.6 x 10(-4) M) sites. Caltractin is highly stable in both the apo- and the Ca(2+)-loaded states. The unusual stability of apocaltractin makes this protein highly suited for structural studies by multidimensional NMR aimed at understanding the structural and dynamic consequences of Ca2+ binding, and the molecular basis of Ca2+ signal transduction.

[The effect of medical treatment on hypertension community control--a follow-up study of more than one thousand hypertensives in East City Proper, Beijing]

Hypertension exerts a great threat on human health. Although most of countries promote the management of hypertension in communities, the role of treatment of hypertension is still controversial, it directly influences the strategy of hypertension community control. This study was based on the survey of essential and borderline hypertension in Gu-lou District of East City Proper, Beijing in 1981, and the management of 1339 hypertensives in the follow-up from 1982 to 1985, and the mortality registration in the district by Disease Surveillance System. By observing the prognosis within one year among different treatment groups (nonusers, less than 9 months and more than 9 months within one year), 1289 patients were followed up for a total of 4283 person-years. Crude analyses, stratified and logistic analyses with multi-variables adjustment of age, sex, blood pressure, with or without end-organ damage, etc. could not find that treatments had obvious effects on the reduction of incidence and mortality of stroke, mortality of CVD and all-cause in hypertensives except severe cases. The stratified analyses dy smoking also showed that smoking had a disadvantageous effects for treated hypertensives. Based on our results, we suggest that health education should be a major part of hypertension management program in community; treatments of hypertension should consider the flexible situation of patients and may not be a priority in hypertension community control program.

Hafnia alvei. Respiratory tract isolates in a community hospital over a three-year period and a literature review

In a retrospective review, a group of seven patients were found to have a sputum culture positive for Hafnia alvei. Hafnia alvei is a Gram-negative enteric and oropharyngeal bacillus and usually is nonpathogenic. All our patients had a chronic underlying illness and one of the patients was endotracheally intubated at the time of the isolation of this organism. Six of seven patients had other organisms isolated along with H alvei, and only one patient had a pure growth of H alvei confirmed by a culture obtained from a bronchoscopic protected brush specimen. All isolates displayed resistance to conventional antibiotics including cephalosporins and penicillins. Although rare, H alvei may be a potential pathogen in a patient with a chronic underlying illness.

A survey of actinic keratoses among paraquat production workers and a nonexposed friend reference group

Follow-up on two reports of an excess of keratoses among paraquat production workers was conducted to evaluate the contribution of occupational exposures to the prevalence of keratoses among workers in a paraquat production plant in Texas. A cross-sectional study design was used to compare the prevalence of keratoses among current workers to an age, race, and sex frequency-matched group of their friends who had never worked at the plant. The analysis is based on 112 workers and 232 friends. Exposure, outcome, and covariables used in the analyses were obtained from an interview questionnaire, dermatology exam, and company records. Overall, the prevalence proportion of the presence of any actinic keratoses among workers and friends was similar (0.30 and 0.28, respectively). Among high cumulative exposed workers, the prevalence of any actinic keratoses was 0.40 compared to 0.20 among low-exposed workers and 0.28 among friends. These results were further explored using a multiple logistic regression approach to adjust for known risk and possibly confounding variables. Statistically significant high risks of actinic keratoses were demonstrated for freckling before age 16 years, older age, suntanning behaviors, occupational exposure to polycyclic aromatic hydrocarbons (PAH), and Fitzpatrick skin type. There was no significant contribution of overall exposure status (worker vs. friend). Similar to the crude analysis, the odds of actinic keratoses of high-exposed workers compared to friends was 1.9 (confidence interval [CI] = 0.9-4.2) whereas the comparable odds ratio for low-exposed workers vs. friends was 0.6 (CI = 0.2-1.7). These data do not demonstrate an excess of actinic keratoses overall nor any consistent increase in the odds of keratoses with an increase in plant exposure level.

Micturition patterns after spinal trauma as a measure of autonomic functional recovery

The purpose of these experiments was to determine whether experimental spinal trauma would result in urological dysfunction similar to that seen clinically and whether recovery of normal micturition can be correlated with motor functional recovery. A standard rat model of spinal impact trauma was employed. Neurologic evaluation included a modified 7 point hindlimb Tarlov scale applied weekly for 4 weeks after injury. Micturition measurement was accomplished by placing the animal in a metabolic cage for 24-hour periods and collecting urine on an electronic scale connected to Lotus Measure data acquisition software. All assessments were performed in a blinded fashion. Animals were categorized as normal control (N = 10), sham injured (N = 11), spinal cord injury (SCI) without (N = 11) and with locomotor recovery (N = 11). There were no differences in total micturition volume among the 4 groups, while the number of micturitions per 24 hours was significantly less for SCI without locomotor recovery (10.4 +/- 5.9) than for control (21.3 +/- 4.5). The volume per micturition was significantly greater for SCI (2.0 +/- 0.7 ml.) than for control (0.8 +/- 0.2 ml.). There were no differences among groups in the ratio of number of micturitions night/day. The SCI group had significantly greater largest and smallest micturitional volumes. Results clearly show alterations in micturition patterns induced by SCI. These were proportional to, but did not correlate fully with, the severity of injury and degree of motor recovery. Thus, recovery of a normal micturition pattern did not occur to the same extent as did motor functional recovery. This difference underscores the potential value of autonomic measures of SCI for distinguishing outcome categories after experimental SCI.

Molecular cloning and centrosomal localization of human caltractin

Caltractin, a 20-kDa calcium-binding protein, was previously purified and cloned at the DNA level from the unicellular green alga Chlamydomonas. It is a structural component of the basal body complex, the major microtubule-organizing center in Chlamydomonas and the functional homolog of the centrosome in the animal cell. Here we report the characterization of a cDNA encoding a human caltractin that shares a high degree of amino acid identity (70%) with its algal counterpart. Caltractin was identified in both HeLa and BHK cells as a 21-kDa polypeptide specifically localized to the centrosome of interphase and mitotic cells. The high level of conservation in the amino acid sequence of caltractin from algae to humans and its association with the major microtubule-organizing center in the cell suggest that caltractin plays a fundamental role in microtubule-organizing center structure and function.

Effects of rhynchophylline on motor activity of mice and serotonin and dopamine in rat brain

Rhynchophylline (Rhy) reduced the spontaneous motor activity and enhanced the sedative and hypnotic effects of sodium pentobarbital in mice. The effects of Rhy on serotonin (5-HT) and dopamine (DA) concentrations in rat brain, and the release of 5-HT and DA from the regional brain slices were studied by a fluorescence detector. Rhy increased the 5-HT content in the hypothalamus and cortex, but reduced the DA concentrations in the cortex, amygdala, and spinal cord. Rhy promoted the release of endogenous DA from 4 brain regions. The release of 5-HT was increased in 2 brain regions and decreased in hypothalamus slice. However, Rhy inhibited the release of both 5-HT and DA evoked by high potassium.

Crystal structure of the Y52F/Y73F double mutant of phospholipase A2: increased hydrophobic interactions of the phenyl groups compensate for the disrupted hydrogen bonds of the tyrosines

The enzyme phospholipase A2 (PLA2) catalyzes the hydrolysis of the sn-2 ester bond of membrane phospholipids. The highly conserved Tyr residues 52 and 73 in the enzyme form hydrogen bonds to the carboxylate group of the catalytic Asp-99. These hydrogen bonds were initially regarded as essential for the interfacial recognition and the stability of the overall catalytic network. The elimination of the hydrogen bonds involving the phenolic hydroxyl groups of the Tyr-52 and -73 by changing them to Phe lowered the stability but did not significantly affect the catalytic activity of the enzyme. The X-ray crystal structure of the double mutant Y52F/Y73F has been determined at 1.93 A resolution to study the effect of the mutation on the structure. The crystals are trigonal, space group P3(1)21, with cell parameters a = b = 46.3 A and c = 102.95 A. Intensity data were collected on a Siemens area detector, 8,024 reflections were unique with an R(sym) of 4.5% out of a total of 27,203. The structure was refined using all the unique reflections by XPLOR to a final R-factor of 18.6% for 955 protein atoms, 91 water molecules, and 1 calcium ion. The root mean square deviation for the alpha-carbon atoms between the double mutant and wild type was 0.56 A. The crystal structure revealed that four hydrogen bonds were lost in the catalytic network; three involving the tyrosines and one involving Pro-68. However, the hydrogen bonds of the catalytic triad, His-48, Asp-99, and the catalytic water, are retained. There is no additional solvent molecule at the active site to replace the missing hydroxyl groups; instead, the replacement of the phenolic OH groups by H atoms draws the Phe residues closer to the neighboring residues compared to wild type; Phe-52 moves toward His-48 and Asp-99 of the catalytic diad, and Phe-73 moves toward Met-8, both by about 0.5 A. The closing of the voids left by the OH groups increases the hydrophobic interactions compensating for the lost hydrogen bonds. The conservation of the triad hydrogen bonds and the stabilization of the active site by the increased hydrophobic interactions could explain why the double mutant has activity similar to wild type. The results indicate that the aspartyl carboxylate group of the catalytic triad can function alone without additional support from the hydrogen bonds of the two Tyr residues.

Light-evoked expansion of subretinal space volume in the retina of the frog

The retina of the frog was superfused with a Ringer solution containing impermeant "probe" cations and anions. Light-evoked concentration changes in these probe ions were measured in the subretinal space (SRS) with ion-selective microelectrodes. A decrease in probe ion concentration was found, and several observations suggest that this is caused by a light-evoked expansion of the SRS. The probe ion decrease was not seen in the isolated retina; thus, the pigment epithelial (PE) cells are important for its generation. Pharmacological studies suggest that K+ channels in the PE cells are important--perhaps the PE cells shrink in response to the light-evoked decrease in SRS [K+]. The light-evoked decrease of SRS volume may be important in the understanding of SRS solute concentrations, retina-PE adhesivity, photoreceptor-PE cell interactions, and the interphotoreceptor matrix.

Embryogenesis and plant regeneration from isolated microspores of Brassica rapa L. ssp. Oleifera

Conditions favourable to embryogenesis from isolated microspores of Brassica rapa L. ssp. oleifera (canola quality) were identified. A population with enhanced responsiveness for microspore embryogenesis (C200) was synthesized by crossing individual plants showing microspore embryogenic potential. For optimal microspore embryogenesis, buds (2-3mm in length, containing mid-late uninucieate microspores) were collected from older plants (2 months old) and microspores isolated and washed in iron-free B5 medium. NLN medium with its iron content reduced to half was beneficial for initial microspore culture. An elevated temperature(33-35°C) during the first day of culture, followed by maintenance at 25°C resulted in dozens of embryos from each isolation (about 100 buds). Seeds were obtained from plants regenerated from microsporederived embryos after colchicine treatment.

Insulin and insulinlike growth factors in embryonic development. Effects of a biologically inert insulin (guinea pig) on rat embryonic growth and development in vitro

Congenital anomalies occur up to four times more frequently in diabetic pregnancy than in the nondiabetic population. Although past work has shown that maternal hyperglycemia and hyperketonemia may increase embryonic abnormalities, recent experimental evidence suggests that low insulin levels may also contribute to diabetic embryopathy. This study investigated the effects of guinea pig serum (whose insulin is inactive in rat systems) on rat embryonic growth and development in culture. Supplementation of guinea pig serum with pork insulin at low (1 ng/ml) and high (5 ng/ml) physiological concentrations and insulinlike growth factors (IGF) I and II were also studied. Culture of rat embryos from the early headfold stage in guinea pig serum resulted in poor embryonic growth and development with a 92% rate of anomalies. Supplementation of guinea pig serum with zinc-binding pork insulin significantly improved rat embryonic growth and development (46% anomaly rate) especially between the first 5 and 21 h of the period of organogenesis. This evidence supports our most recent findings that low insulin levels, as encountered in untreated diabetic pregnancy, may contribute to the increased risk of congenital abnormality. Insulin at low physiological concentrations improved growth, whereas higher physiological concentrations were required to increase growth and development. IGF-I or IGF-II supplementation improved rat embryonic growth and development but failed to match that of the controls, indicating that other growth factors including insulin may also be required.

Evaluation of transgenic canola plants under field conditions

Eleven independent transgenic canola (Brassica napus ssp. oleifera L. cv. Westar and Regent) lines were evaluated in the field. The plants carried a neomycin phosphotransferase (NPTII) gene for kanamycin resistance that was introduced via Agrobacterium-mediated transformation. NPTII enzyme assays, Southern blot by hybridizations and progeny analysis, confirmed the stable, heritable integration and expression of the introduced NPTII gene. A number of agronomic characteristics evaluated under field conditions, including maturity yield, and oil and protein content, were all statistically comparable between the transformed and nontransforemd platns. These results indicate that canola can be genetically engineered successfully, and that the Agrobacterium-based transformation system employed does not induced any adverse effects on the intrinsic agronomic and qualitative traits critical to the agricultural industry.

Cellular reaction to the Vascugraft polyesterurethane vascular prosthesis: in vivo studies in rats

The biocompatibility of Vascugraft, a polyesterurethane vascular prosthesis manufactured by Braun-Melsungen AG, was assessed by immunofluorescence and histological studies. Discs, 1 cm2, of Vascugraft prosthesis were implanted into the peritoneal cavity of rats. Results were compared with Impra, GORE-TEX and Mitrathane prostheses and a control group. Animals were killed at 1, 2, 6, 9 and 12 wk. Total T cells, T helper cells, T suppressor cells and activated T lymphocytes expressing Interleukin-2 receptors were quantified by a cytofluorometric technique in the peripheral blood of rats. For each period of implantation, all vascular prostheses showed no significant change in the percentage of total T cells, T subsets and T cells expressing Interleukin-2 receptors when compared to the control group. Histological examination of the tissue reaction surrounding the Vascugraft revealed a mild inflammatory reaction, similar to the one observed with both polytetrafluoroethylene grafts. However, the rate and the degree of encapsulation were different between grafts. The Vascugraft prosthesis was well encapsulated 2 wk after implantation, whereas inhibition of fibroblastic proliferation into the graft wall and surrounding both polytetrafluoroethylene grafts was observed for each period of implantation. The Mitrathane prosthesis exhibited a moderate inflammatory response, characterized by a high level of activation on fibroblasts compared to other grafts.

Genomic structure of Chlamydomonas caltractin. Evidence for intron insertion suggests a probable genealogy for the EF-hand superfamily of proteins

A clone containing the gene locus for Chlamydomonas caltractin, a 20,000 Mr calcium-binding protein that is a member of the EF-hand superfamily of calcium-modulated proteins, was isolated and the structural organization of the gene was determined. The intron-exon organization was resolved by direct comparison of the genomic sequence with a caltractin cDNA. The promoter region does not contain the typical TATA or CCAAT boxes, but the sequences at the splice junctions are similar to those of other eukaryotes. The positions of the six introns in the caltractin gene do not typically define unit structures, nor do they coincide with those in genes for other members of the EF-hand superfamily. An analysis of exon sequences at the splice junctions in the genes of this multigene family was undertaken; evidence was obtained that supports the hypothesis that introns arose at proto-splice sites. A probable evolutionary history for the EF-hand superfamily based on intron insertion is offered.

Comparison of pharmacological agents (aspartate vs. aminophosphonobutyric plus kynurenic acids) to block synaptic transmission from retinal photoreceptors in frog

The combination of aminophosphonobutyric plus kynurenic acids (APB/Kyn) was compared to aspartate with respect to its ability to block synaptic transmission from photoreceptors. Like aspartate, APB/Kyn blocks photoreceptor synaptic transmission, as monitored by the b- and d-waves of the electroretinogram, by the proximal negative response and M-wave of the proximal retina, and by the light-evoked increase in extracellular K+ concentration in the inner plexiform layer. Unlike aspartate, APB/Kyn has relatively minor effects on retinal resistance, light-evoked changes in K+ and Ca2+ concentrations in the subretinal space, light-evoked changes in subretinal space volume, resting extracellular concentrations of K+ and Ca2+ in the proximal and distal retina, and the c-wave. Effects of APB/Kyn are generally more reversible than effects of Asp. A disadvantage of APB/Kyn is that the a-wave usually becomes smaller and slower. Overall, APB/Kyn disrupts the retina less than aspartate. Therefore, in some situations in which blockade of photoreceptor synaptic transmission is desired, the use of APB/Kyn may be preferable to that of aspartate.

The colR4 and colR15 beta-tubulin mutations in Chlamydomonas reinhardtii confer altered sensitivities to microtubule inhibitors and herbicides by enhancing microtubule stability

The colR4 and colR15 beta 2-tubulin missense mutations for lysine-350 in Chlamydomonas reinhardtii (Lee and Huang, 1990) were originally isolated by selection for resistance to the growth inhibitory effects of colchicine. The colR4 and colR15 mutants have been found to be cross resistant to vinblastine and several classes of antimitotic herbicides, including the dinitroanilines (oryzalin, trifluralin, profluralin, and ethafluralin); the phosphoric amide amiprophos methyl; and the dimethyl propynl benzamide pronamide. Like colchicine and vinblastine, the antimitotic effects of these plant-specific herbicides have been associated with the depolymerization of microtubules. In contrast to their resistance to microtubule-depolymerizing drugs, the mutants have an increased sensitivity to taxol, a drug which enhances the polymerization and stability of microtubules. This pattern of altered sensitivity to different microtubule inhibitors was found to cosegregate and corevert with the beta-tubulin mutations providing the first genetic evidence that the in vivo herbicidal effects of the dinitroanilines, amiprophos methyl, and pronamide are related to microtubule function. Although wild-type like in their growth characteristics, the colR4 and colR15 mutants were found to have an altered pattern of microtubules containing acetylated alpha-tubulin, a posttranslational modification that has been associated with stable subsets of microtubules found in a variety of cells. Microtubules in the interphase cytoplasm and those of the intranuclear spindle of mitotic cells, which in wild-type Chlamydomonas cells do not contain acetylated alpha-tubulin, were found to be acetylated in the mutants. These data taken together suggest that the colR4 and colR15 missense mutations increase the stability of the microtubules into which the mutant beta-tubulins are incorporated and that the altered drug sensitivities of the mutants are a consequence of this enhanced microtubule stability.

Missense mutations at lysine 350 in beta 2-tubulin confer altered sensitivity to microtubule inhibitors in Chlamydomonas

Two beta-tubulin mutants of Chlamydomonas reinhardtii, colR4 and colR15, were previously isolated in our laboratory. Each mutant expressed an acidic beta-tubulin variant as a result of an alteration in the coding sequence of one of the two beta-tubulin genes in C. reinhardtii, which in the wild type encode identical proteins. In this report, we describe the identity of the specific beta-tubulin altered in the colR mutants and the precise nature of the genetic lesions. Hybrid selection of mutant poly(A)+ RNA with cDNA probes specific for the two beta-tubulins in C. reinhardtii indicated that both mutations resided in the beta 2-tubulin gene. cDNA libraries were constructed with mutant poly(A)+ RNA, and beta 2-tubulin cDNA clones were isolated. Results of in vitro transcription of cloned beta 2-tubulin cDNAs confirmed the identity of the altered genes. Sequencing of the entire coding regions of the beta 2-tubulin cDNA clones revealed that the mutants carried different single-base substitutions in the same codon for the amino acid at position 350 in the beta 2-tubulin sequence, effecting a change from a lysine to a glutamic acid in the colR4 variant and to a methionine in the colR15 variant. These changes in amino acids are consistent with the difference in the charge of the two variant polypeptides observed in isoelectric focusing. Because both the colR4 and colR15 mutations confer an altered sensitivity to a number of different microtubule inhibitors and herbicides, lysine 350 appears to be of functional importance in the structure of the tubulin molecule.

Effects of culture density, conditioned medium and feeder cultures on microspore embryogenesis in Brassica napus L. cv. Topas

In microspore cultures of Brassica napus L. cv. Topas, embryo yield increases with culture density up to about 40,000 microspores per ml. A much higher density (100,000 per ml) appears inhibitory to embryogenesis. A relatively high culture density (30,000 or 40,000 per ml) for the first 2-4 days of culture is crucial for embryogenesis, after which cultures may be diluted to allow better embryo growth.Medium conditioned by culturing microspores at 30,000 or 40,000 per ml for 1 day improved microspore-embryo yield in low density cultures (3,000 or 4,000 per ml) more than 3-fold. In contrast, media conditioned with microspores from 1-4 days or 0-4 days of culture were inhibitory.Use of feeder cultures resulted in up to 10-fold increase of embryo yield in low density microspore cultures, depending on the method used. Filter papers and other membranes placed on top of feeders greatly inhibited embryogenesis in the feeder layer as well as microspores cultured on the feeder, possibly due to poorer gaseous exchange.

Light-evoked changes in extracellular calcium concentration in frog retina

Light-evoked changes in extracellular Ca2+ concentration were recorded with Ca2(+)-selective microelectrodes in the retina of the frog eyecup. A Ca-decrease at light onset and offset was found in the inner plexiform layer, and its properties are consistent with it resulting from Ca2+ influx into activated neuronal terminals. In the subretinal space, a Ca-increase at light onset and a Ca-decrease at offset were observed, and these likely arise directly from photoreceptors. A slower ON Ca-decrease was also seen here. Because it survives pharmacological isolation of the photoreceptors from post-synaptic interactions, but not physical isolation of the retina from the pigment epithelium, this component probably depends on pigment epithelial activity.