Intracellular pH in arbuscular mycorrhizal fungi. A symbiotic physiological marker

A method was developed to perform real-time analysis of cytosolic pH of arbuscular mycorrhizal fungi in culture using dye and ratiometric measurements (490/450 nm excitations). The study was mainly performed using photometric analysis, although some data were confirmed using image analysis. The use of nigericin allowed an in vivo calibration. Experimental parameters such as loading time and concentration of the dye were determined so that pH measurements could be made for a steady-state period on viable cells. A characteristic pH profile was observed along hyphae. For Gigaspora margarita, the pH of the tip (0-2 &mgr;m) was typically 6.7, increased sharply to 7.0 behind this region (9.5 &mgr;m), and decreased over the next 250 &mgr;m to a constant value of 6.6. A similar pattern was obtained for Glomus intraradices. The pH profile of G. margarita germ tubes was higher when cultured in the presence of carrot (Daucus carota) hairy roots (nonmycorrhizal). Similarly, extraradical hyphae of G. intraradices had a higher apical pH than the germ tubes. The use of a paper layer to prevent the mycorrhizal roots from being in direct contact with the medium selected hyphae with an even higher cytosolic pH. Results suggest that this method could be useful as a bioassay for studying signal perception and/or H+ cotransport of nutrients by arbuscular mycorrhizal hyphae.

Comparison of auditory and visual feedback for EMG training.

27 undergraduate students participated in an experiment on EMG biofeedback. Three groups were employed (visual feedback, audio biofeedback, and control) to determine which group learned to reduce frontalis muscle tension more quickly. All subjects were trained during a 30-min. period for five days. The time consisted of a 10-min. baseline and a 20-min. biofeedback session. Over a 5-day period relaxation in the forehead due to biofeedback improved significantly. More training time yielded an increased relaxation in this area, and most learning occurred during the first two days. The significant interaction of training and time illustrated that the two biofeedback groups produced a more pronounced relaxation in the forehead muscle than did the control group. No significant difference was found between the two biofeedback groups.

A simple method for quantifying specific mRNAs in small numbers of early mouse embryos.

Amplification of sequences by the polymerase chain reaction (PCR) has become a powerful tool in the study of gene expression. The technique is, in fact, so powerful that it may detect 'leaky transcription'. Thus, it is now important to be able to quantify the transcripts that are amplified to determine whether or not they represent legitimate transcription of target genes. In this paper, we describe a one-step amplification reaction coupled to solution hybridization/RNase protection that is capable of quantitating specific transcripts in total RNA from one to ten preimplantation mouse embryos and is generally applicable to any cloned mRNA sequence.

Replication forks are underrepresented in chromosomal DNA of Xenopus laevis embryos.

Chromosomal DNA was isolated from rapidly dividing cells of Xenopus laevis embryos at blastulation, at gastrulation, and at the beginning of hatching. Few, if any, replication forks were seen by electron microscopy in DNA isolated at any stage of embryogenesis. Instead, unbranched DNA, which appeared to be single-stranded, was abundant at all stages. The percentage of chromosomal DNA that was single-stranded was quantitated by electron microscopy and by monitoring the release of acid-soluble radioactivity during digestion of labeled chromosomal DNA with nucleases specific for single-stranded DNA. The amount of single-stranded DNA was inversely correlated with the length of S phase during embryogenesis. We postulate that chromosomal DNA replication in X. laevis embryos takes place by a mechanism in which strand separation is uncoupled from DNA synthesis.

Process-oriented administration of the picture arrangement test does not affect the quantitative outcome.

Extracting the maximum amount of qualitative information of cognitive functioning from tests is one of the major goals, of the process approach to neuropsychological assessment. This study examined whether there is a difference in score in the Picture Arrangement (PA) test of the Wechsler Adult Intelligence Scale-Revised for participants who completed the standardized versus a process-oriented administration (i.e., asking the person to "tell the story" immediately following each item). Eighteen traumatic brain injury patients and 20 control participants (i. e., non-brain-injury volunteers) were randomly assigned to the standardized administration or the process-oriented administration of the PA test. A 2 x 2 (Group x Type of Administration) analysis of variance revealed no statistically significant interaction effect or main effect for type of administration. Therefore, the process of maximizing the elicitation of qualitative information does not appear to affect the quantitative outcome of the PA test.

Current status of SOD1 mutations in familial amyotrophic lateral sclerosis.

Twenty percent of cases of familial amyotrophic lateral sclerosis (FALS) have identifiable mutations in the gene for Cu, Zn superoxide dismutase (SOD1) located on the long arm of chromosome 21. SOD1 mutations are thought to cause a yet unknown toxic gain of function resulting in motor neuron damage. Seventy-one mutations, located in all five exons of SOD1, have been reported. Identified mutations are predominantly heterozygous mis-sense mutations, although rare nonsense mutations, deletions, and insertions exist. While gene dosage has an effect on the age of onset, genotoype/phenotype correlation is better defined for progression of symptoms than for disease onset.

Effect on embryos of injection of phosphorothioate-modified oligonucleotides into pregnant mice.

Phosphorothioate-modified oligonucleotides were injected into pregnant female mice to assess the effect on developing embryos. Injections were carried out during two different time periods, one when embryos were in preimplantation stages of development (about 3.5 days of development) and the other after implantation, when both a fetus and placenta are present (from days 9.5 to 11.5 of development). Three different phosphorothioate-modified oligonucleotides were injected. One, which had a sequence not present in the mouse genome, was used to ask whether nonspecific toxic or teratogenic effects on embryos result from treatment of the mother. A second was complementary to the mRNA of the testis-determining factor gene Sry and was used to ask whether a specific developmental pathway (i.e., sex determination) could be disrupted in embryos in vivo. The third was the complement of the anti-Sry sequence. None of these oligonucleotides reduced the frequency of successful pregnancy after mating or the average litter size from that observed in controls animals. Furthermore, examination of 291 pups or fetuses from all oligonucleotide-injected pregnant females revealed no developmental defects regardless of which sequence was used. It is concluded that injection of phosphorothioate-modified oligonucleotides into pregnant females according to the protocols described here is not toxic or teratogenic to embryos in a nonspecific way. Also, anti-Sry oligonucleotides did not influence sex determination in embryos, although there are several possible explanations for this.

Expression of the mouse testis-determining gene Sry in male preimplantation embryos.

The testis-determining factor in the mouse is encoded by the Sry gene on the Y chromosome. Transcripts of this gene have been shown previously to be present in the genital ridge at the beginning of gonadal differentiation (11.5 days post coitum) and in adult testis. In this study, RNA transcripts of the Sry gene are also detected in male blastocyst-stage embryos (3.5 days post coitum) at approximately 40-100 copies per cell, long before overt sex differentiation. These results indicate that preimplantation mouse embryos have sexually dimorphic gene expression at least with respect to Sry transcripts. In addition, at least some of the Sry RNA transcripts in blastocysts are circular, as has been reported for Sry transcripts from adult testis. The appearance of Sry transcripts in blastocysts at this level raises the possibility that sex determination begins earlier during embryonic development than previously thought.

Mutually exclusive expression of the Strongylocentrotus purpuratus Spec1 gene and its Lytechinus pictus homologue in cells of hybrid embryos.

The expression of the Spec1 gene of Strongylocentrotus purpuratus and its Lytechinus pictus homologue LpS1 was analyzed in reciprocal hybrid embryos of these two species of sea urchin. While the time course of accumulation of Spec1 mRNA was nearly normal in hybrid embryo populations, the accumulation of LpS1 mRNA was not. This was particularly evident in plutei, where the level of LpS1 mRNA was less than 5% that in normal L. pictus plutei. In situ hybridization analysis of serial sections indicated that LpS1 mRNA was detectable in only about 2% of hybrid plutei in either cross, whereas Spec1 mRNA was present in nearly all hybrid plutei; expression of either homologue was appropriately restricted to the aboral ectoderm. In crosses of L. pictus eggs with S. purpuratus sperm (LpSp), about 1% of hybrid plutei expressed LpS1 RNA in most or all aboral ectoderm cells at normal levels, and did not express Spec1 RNA; in another 1% of the LpSp hybrid plutei the Spec1 and LpS1 transcripts were present at normal levels in complementary, non-overlapping patches of contiguous aboral ectoderm cells. In the reciprocal SpLp cross, each hybrid pluteus expressed either only the LpS1 gene (about 2%) or only the Spec1 gene throughout the aboral ectoderm. In SpLp hybrid gastrulae the level of LpS1 mRNA was less restricted; about 2% of the embryos contained only LpS1 RNA, and about half expressed only Spec1 transcripts, but in the remaining embryos Spec1 and LpS1 transcripts were coexpressed in the same aboral ectoderm cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The mutation rates of di-, tri- and tetranucleotide repeats in Drosophila melanogaster.

In a recent study, we reported that the combined average mutation rate of 10 di-, 6 tri-, and 8 tetranucleotide repeats in Drosophila melanogaster was 6.3 x 10(-6) mutations per locus per generation, a rate substantially below that of microsatellite repeat units in mammals studied to date (range = 10(-2)-10(-5) per locus per generation). To obtain a more precise estimate of mutation rate for dinucleotide repeat motifs alone, we assayed 39 new dinucleotide repeat microsatellite loci in the mutation accumulation lines from our earlier study. Our estimate of mutation rate for a total of 49 dinucleotide repeats is 9.3 x 10(-6) per locus per generation, only slightly higher than the estimate from our earlier study. We also estimated the relative difference in microsatellite mutation rate among di-, tri-, and tetranucleotide repeats in the genome of D. melanogaster using a method based on population variation, and we found that tri- and tetranucleotide repeats mutate at rates 6.4 and 8.4 times slower than that of dinucleotide repeats, respectively. The slower mutation rates of tri- and tetranucleotide repeats appear to be associated with a relatively short repeat unit length of these repeat motifs in the genome of D. melanogaster. A positive correlation between repeat unit length and allelic variation suggests that mutation rate increases as the repeat unit lengths of microsatellites increase.

The distribution and frequency of microsatellite loci in Drosophila melanogaster.

We report the results of a comprehensive search of Drosophila melanogaster DNA sequences in GenBank for di-, tri-, and tetranucleotide repeats of more than four repeat units, and a DNA library screen for dinucleotide repeats. Dinucleotide repeats are more abundant (66%) than tri- (30%) or tetranucleotide (4%) repeats. We estimate that 1917 dinucleotide repeats with 10 or more repeat units are present in the euchromatic D. melanogaster genome and, on average, they occur once every 60 kb. Relative to many other animals, dinucleotide repeats in D. melanogaster are short. Tri- and tetranucleotide repeats have even fewer repeat units on average than dinucleotide repeats. Our WorldWide Web site (http://www.bio.cornell.edu/genetics/aquadro/+ ++aquadro.html) posts the complete list of 1298 microsatellites (> or = five repeat units) identified from the GenBank search. We also summarize assay conditions for 70 D. melanogaster microsatellites characterized in previous studies and an additional 56 newly characterized markers.