Experiment to Detect Dark Energy Forces Using Atom Interferometry

The accelerated expansion of the universe motivates a wide class of scalar field theories that modify general relativity (GR) on large scales. Such theories require a screening mechanism to suppress the new force in regions where the weak field limit of GR has been experimentally tested. We have used atom interferometry to measure the acceleration of an atom toward a macroscopic test mass inside a high vacuum chamber, where new forces can be unscreened. Our measurement shows no evidence of new forces, a result that places stringent bounds on chameleon and symmetron theories of modified gravity.

cDNA sequence and genomic structure of the murine p55 (Mpp1) gene

MPP1 is an X-linked human gene encoding a heavily palmitoylated membrane protein (p55) with homology to the Drosophila tumor suppressor gene lethal(1) discs-large. As a first step toward studying the effects of mutations in this gene in a mammalian system, the nucleotide sequence of the mouse Mpp1 cDNA has been determined along with the intron-exon boundaries. Mpp1 is ubiquitously expressed and encodes a p55 protein of 466 amino acids with 93 and 65% identity to the human and puffer fish (Fugu rubripes) p55 sequences, respectively. The genomic structure of the Mpp1 gene is likewise conserved with 12 exons. The location of the Mpp1 gene, on the X chromosome, is also conserved between the human and the mouse. Conservation of the Mpp1 gene between mouse and human gives support to the notion that construction and study of a mouse knockout model may help establish the function of the human MPP1 gene, a potential tumor suppressor gene.

The mottled gene is the mouse homologue of the Menkes disease gene

The mottled mouse has been proposed as an animal model for Menkes disease, an X-linked disorder of copper transport. The recent isolation of a copper-transporting ATPase gene responsible for Menkes disease has allowed us to test this hypothesis. Here we report the isolation and sequence of the mouse homologue of this gene. We show that two mottled (Mo) alleles, dappled (Modp) and blotchy (Moblo), have abnormalities in the murine mRNA and that Modp has a partial gene deletion. These studies prove that the mottled mouse is the murine model for Menkes disease, providing the basis for future biochemical and therapeutic studies.

Sequence of the murine factor VIII cDNA

DNA clones corresponding to the mouse homolog of the human factor VIII gene have been isolated and sequenced. The murine gene is expressed in most tissues examined and the mRNA is approximately 1.8 kb smaller than the human transcript, primarily due to a shorter 3' untranslated region. The mouse cDNA encodes a protein of 2319 amino acids, 32 amino acids shorter than human factor VIII, with 74% identity to the human sequence. Further comparison shows that amino acid sequences in the functionally important A and C domains are highly conserved (84-93% identity), whereas the B domains and the two acidic domains are more divergent (42-70% identity). All thrombin/factor Xa cleavages sites and all but one activated protein C cleavage site are conserved in mouse factor VIII, as well as a tyrosine residue needed for von Willebrand factor binding. These findings suggest that mouse factor VIII operates in the clotting cascade much like the human protein, but reveal some differences that may have functional significance.

Unusual distribution of Zfy and Zfx sequences on the sex chromosomes of the wood lemming, a species exhibiting XY sex reversal

Sex reversal occurs naturally in the wood lemming (Myopus schisticolor) due to the presence in populations of this species of a variant (mutated) X chromosome, designated X*. Thus, X*Y animals develop into females, whereas XY animals develop into normal males. Chromosome mapping by in situ hybridization of DNA sequences homologous to the human ZFY gene localized the wood lemming Zfx sequences to region p12----p11 on both the wild-type X and the mutated X* chromosomes, at or proximal to a presumed breakpoint (Xp12) involved in the generation of the X* chromosome from the normal X, and Zfy sequences along the entire short arm of the Y chromosome. Differences between Zfx and Zfx* were readily detected by Southern blot analysis. However, both the Zfx and Zfx* genes expressed similarly sized transcripts in all adult somatic tissues investigated. Although the precise molecular difference between the Zfx and Zfx* genes is still unknown, their chromosomal location suggests that either Zfx or some other closely linked gene(s) on the X chromosome may be a major X-linked sex-determining gene, Tdx, which in the X* chromosome fails to interact properly with the Y-linked testis-determining gene, Tdy, thus causing X*Y embryos to develop into females. At least 15 copies of wood lemming Zfy sequences are distributed along the short arm of the Y chromosome. Northern hybridization analyses of adult tissues and somatic cell lines indicated that these Zfy repeats were transcriptionally inactive. Normally, 3-kb Zfy (ZFY) transcripts are readily detected in mouse and human testes, especially in the germ cells. It has therefore been postulated that expression of the Zfy (ZFY) gene may be important for spermatogenesis. Whether the lack of sufficient Zfy transcripts in the testis of the adult wood lemming has any impact on spermatogenesis in this species is still to be elucidated by further studies.

The free cytoplasmic Ca2+ levels in duchenne muscular dystrophy lymphocytes

An increased cellular Ca2+ content has been associated with Duchenne muscular dystrophy (DMD). However, estimates of the free cytoplasmic Ca2+ concentration ([Ca2+]i) in cells of DMD patients were not available. We compared the [Ca2+]i levels of normal and DMD peripheral blood lymphocytes and Epstein-Barr virus-transformed lymphoblasts using the novel probe, quin 2, an internally trapped fluorescent indicator. The [Ca2+]i levels of normal and DMD cells were not significantly different.

Phorbol ester-induced changes of cytoplasmic pH in neutrophils: role of exocytosis in Na+-H+ exchange

Cytoplasmic pH homeostasis was studied in intact and granule-free porcine neutrophils following activation with 12-O-tetradecanoyl-phorbol-13-acetate (TPA). In intact cells, TPA activated at least two separate processes: a Na+-independent and amiloride-insensitive acidification, and a compensatory acid extrusion. The latter is Na+ dependent and blocked by amiloride and is likely to represent Na+-H+ exchange. Enucleated and degranulated neutrophils (cytoplasts) were prepared by sedimentation of cytochalasin B-treated neutrophils through a discontinuous density gradient. Cytoplasts responded to an artificially imposed acid load with activation of an amiloride-sensitive Na+-H+ exchange. TPA also activated both acid production and Na+-dependent acid extrusion in cytoplasts. The magnitude of the responses was comparable in intact neutrophils and in cytoplasts. These data suggest that 1) the nucleus and the secretory granules are not involved in the acidifying response to TPA, and 2) exocytosis of secretory vesicles is not required for activation of Na+-H+ exchange during acid loading or following treatment with the phorbol ester TPA.

Is cytoplasmic Ca2+ in lymphocytes elevated in cystic fibrosis?

An increased cytoplasmic Ca2+ concentration ( [Ca2+]i) has been implicated in the pathogenesis of cystic fibrosis. We compared the [Ca2+]i levels of normal and cystic fibrosis peripheral blood lymphocytes and Epstein-Barr virus-transformed lymphoblasts using quin 2, an internally trapped indicator. The [Ca2+]i levels of normal and cystic fibrosis cells were not significantly different. The ionophore-releasable intracellular Ca2+ stores were also comparable in both types of individual.

Pigment mutations associated with altered circadian rhythms in mice

Mammalian albinism is known to alter neural pathways, reduce retinal pigment, and affect diverse behaviors. Mammalian circadian rhythms have been shown to depend on visual pathways, respond to light intensity and regulate many behaviors. Here we show that mice homozygous for the recessive albino or pinkeye-dilute mutations display shorter circadian rhythms than pigmented controls. We conclude that these pigment loci, or closely linked loci, influence the expression of circadian rhythms in mice.