Vortex configurations, matching, and domain structure in large arrays of artificial pinning centers

High-resolution scanning Hall probe microscopy has been used to image vortex configurations in very large periodic arrays of artificial pinning sites. Strong matching effects are seen at fields where either one or two vortices can sit at a site; with three vortices per site, however, no clear matching is observed. Matching effects have also been observed at several fractional multiples of the matching field, including 1/5, 1/4, 1/3, 1/2, and 3/4. These fractional values are characterized by striking domain structure and grain boundaries.

A Brg1 null mutation in the mouse reveals functional differences among mammalian SWI/SNF complexes

Mammalian SWI/SNF complexes utilize either brahma (Brm) or brahma-related gene 1 (Brg1) catalytic subunits to remodel nucleosomes in an ATP-dependent manner. Brm was previously shown to be dispensable, suggesting that Brm and Brg1 are functionally redundant. To test this hypothesis, we have generated a Brg1 null mutation by gene targeting, and, surprisingly, homozygotes die during the periimplantation stage. Furthermore, blastocyst outgrowth studies indicate that neither the inner cell mass nor trophectoderm survives. However, experiments with other cell types demonstrate that Brg1 is not a general cell survival factor. In addition, Brg1 heterozygotes are predisposed to exencephaly and tumors. These results provide evidence that biochemically similar chromatin-remodeling complexes have dramatically different functions during mammalian development.

Serial echocardiographic measurements of the pulmonary autograft in the aortic valve position after the Ross operation in a pediatric population using normal pulmonary artery dimensions as the reference standard

Serial echocardiographic measurements of the annulus and sinus were obtained in children before the Ross operation, and early and late postoperatively. Values were compared with normal standards for the aorta and pulmonary artery (PA). There was no significant difference between PA annulus measurements before surgery and the corresponding autograft immediately afterward (1.73 +/- 0.60 cm preoperatively; 1. 63 +/- 0.58 cm postoperatively, p = NS). Late after surgery the mean annulus diameter was enlarged compared with the normal aorta (DeltaZ 1.9 +/- 2.4), but remained relatively unchanged compared with the normal PA (DeltaZ 0.7 +/- 1.1, p <0.01). In contrast, the autograft sinus was dilated early after surgery (1.83 +/- 0.58 cm preoperatively; 2.18 +/- 0.73 cm postoperatively, p <0.01). Mean sinus Z score further increased compared with both the aorta (DeltaZ 1.3 +/- 1.7) and PA (DeltaZ 1.3 +/- 1.6). Use of standard PA measurements may be important in the assessment of autograft enlargement. Minimal change in autograft Z scores over time suggests that annulus enlargement is mainly due to somatic growth. In contrast, the autograft sinus showed an immediate and continued disproportionate increase in size over time, suggesting that sinus enlargement is largely due to passive dilation.

Heteromeric complexes of alpha 5 and/or alpha 7 subunits. Effects of calcium and potential role in nicotine-induced presynaptic facilitation

Nicotine alters a broad spectrum of behaviors, including attention, arousal, anxiety, and memory. The cellular physiology of nicotine is comparably diverse: nicotine interacts with an array of ionotropic receptors whose gating can lead to direct depolarization of neurons or to an indirect modulation of neuronal excitability by presynaptic facilitation. Furthermore, as many laboratories have shown, the alpha- and beta-type subunits that comprise neuronal nicotinic acetylcholine receptors (nAChRs) are encoded by multiple, homologous genes, yielding at least seven alpha and three beta subunits, distinct in primary sequence. nAChRs that differ in subunit composition differ in pharmacology, conductance, and kinetics as well as in their permeability to and modulation by calcium. We will first discuss recent studies on the biophysics of a special (peculiar?) subset of nAChRs, focusing on heteromeric nAChRs comprised of alpha 4 beta 2 +/- alpha 5 or alpha 7 +/- beta 2 and alpha 5. These nAChR channel subtypes are potently and differentially modulated by changes in intracellular calcium ([Ca]). Thus, the Po, tau o, and desensitization kinetics of alpha 4 beta 2 channels are altered by changes in [Ca]int from 0 to 50 microM; nAChRs that include the alpha 5 subunit are oppositely regulated. Mutagenesis of specific residues within the M1 and M2 domain of alpha 4, beta 2, and alpha 5 suggest a possible Ca binding "pocket." The assembly of functional nAChRs that include alpha 5 and/or alpha 7 and the potential role of these novel heteromeric complexes in presynaptic facilitation will also be presented.

The cloning expression and tissue distribution of human PP2Cbeta

We have cloned a novel PP2Cbeta isoform from a human liver cDNA library which codes for a protein homologous to other mammalian PP2Cbetas at the N-terminus but with an extended C-terminus that is unique amongst the PP2Cs. The protein expressed in E. coli is indistinguishable from human recombinant PP2Calpha in its cation dependence and insensitivity to okadaic acid. Northern blot analysis of PP2Cbeta along with that of PP2Calpha shows that human PP2Cs are widely expressed and are most abundant in heart and skeletal muscle.

Complex Y chromosome aberrations are a recurrent secondary event in radiation-induced murine acute myeloid leukaemia

Arbitrarily primed-PCR analysis of DNA from male CBA/H radiation-induced leukaemic spleens revealed the loss of an approximately 350-bp sequence in several leukaemias. We have isolated a lambda EMBL3 C57BL/6 genomic subclone (pJB1) which hybridizes to the AP-PCR probe and is located on the Y chromosome. Southern blot analyses using the pJB1 probe indicate that the genomic sequence was deleted in five of 14 leukaemias. Cytogenetic analyses of 31 X-ray induced leukaemias in male CBA/H mice revealed, in addition to the characteristic partial deletion of chromosome 2 (28/31 leukaemias), a high incidence (16/31) of the loss of an intact Y chromosome. Comparison of the Southern blot and cytogenetic analyses of the leukaemias demonstrate a significant lack of correspondence between the loss of an intact Y chromosome and Y chromosome-specific DNA sequences, suggesting that Y chromosome aberrations are complex. Whereas partial deletion of chromosome 2 can be detected in 6% of bone marrow cells within 6-11 days of irradiation, no Y chromosome involvement was detected, indicating that Y chromosome aberrations are a late event in radiation-induced leukaemogenesis. These findings are comparable to the loss of sex chromosomes in human t(8;21) AML.

An ATF/CREB-binding site is essential for cell-specific and inducible transcription of the murine MIP-1 beta cytokine gene

The murine macrophage inflammatory protein 1 beta mRNA (MIP-1 beta) is rapidly and transiently induced in macrophages by lipopolysaccharide (LPS), serum or cycloheximide. Functional studies of the MIP-1 beta proximal promoter indicate that it is cell-specific, and serum- and LPS-responsive in macrophages. A 76-bp proximal promoter sequence (-51 to -127 bp) confers cell-specific and LPS-inducible activity when placed upstream from a heterologous promoter in both orientations. One essential cis-regulatory element within the enhancer-like sequence is an activating transcription factor/cAMP response element (CRE)-binding protein (ATF/CREB)-binding site, although the promoter is not cAMP responsive. Electrophoretic mobility shift assays and mutational analyses suggest that the promoter site is bound by nuclear protein complexes containing cAMP-independent members of the ATF/CREB family of proteins and c-Jun, and are functionally distinct from the AP1-related TPA-response element (TRE) binding activity.

brg1: a putative murine homologue of the Drosophila brahma gene, a homeotic gene regulator

To identify potential regulators of Hox gene expression in mice, we have screened for genes highly related to brahma (brm), an activator of homeotic gene expression in Drosophila. We have cloned a murine gene, brg1, which, like brm, encodes a member of the DEGH protein family, suggesting that brg1 may be a DNA-dependent ATPase or a helicase. brg1 also contains a bromodomain which may be involved in transactivation. Although the sequences of a number of mammalian genes similar to Drosophila brm have been reported, they are related to brm only within specific portions of the putative helicase region, while brg1 is highly similar to brm throughout and outside of this region. A 5.8-kb brg1 transcript was detected throughout embryogenesis and in numerous adult tissues. RNA in situ hybridization revealed widespread expression of brg1 in embryonic tissues. At later stages of embryogenesis, differences in levels of brg1 expression were seen among different tissues. brg1 expression was highest in the spinal cord, the brain, parts of the peripheral nervous system, and the vertebral column. These expression domains within the spinal cord and vertebral column encompass major regions of Hox gene expression. Within the spinal cord, brain, and retina, mRNA levels were higher in regions consisting of differentiated cells than in regions consisting of undifferentiated, proliferating cells. These patterns of brg1 expression are consistent with a possible role for brg1 in Hox gene regulation as well as in other regulatory pathways.

Two distinct signal transmission pathways in T lymphocytes are inhibited by complexes formed between an immunophilin and either FK506 or rapamycin

Proliferation and immunologic function of T lymphocytes are initiated by signals from the antigen receptor that are inhibited by the immunosuppressant FK506 but not by its structural analog, rapamycin. On the other hand, interleukin 2 (IL-2)-induced signals are blocked by rapamycin but not by FK506. Remarkably, these two drugs inhibit each other's actions, raising the possibility that both act by means of a common immunophilin (immunosuppressant binding protein). We find that the dissociation constant of rapamycin to the FK506 binding protein FKBP (Kd = 0.2 nM) is close to the dissociation constant of FK506 to FKBP (Kd = 0.4 nM) and to their effective biologic inhibitory concentrations. However, an excess of rapamycin is needed to revert FK506-mediated inhibition of IL-2 production, apoptosis, and transcriptional activation of NF-AT, a T-cell-specific transcription factor necessary for IL-2 gene activation. Similarly, an excess of FK506 is needed to revert rapamycin-mediated inhibition of IL-2-induced proliferation. The drug concentrations required for antagonism may be explained by the relative affinity of the drugs to, and by the abundance of, the immunophilin FKBP. FKBP has been shown to catalyze the interconversion of the cis- and trans-rotamers of the peptidyl-prolyl amide bond of peptide substrates; here we show that rapamycin, like FK506, is a potent inhibitor of the rotamase activity of FKBP (Ki = 0.2 nM). Neither FKBP binding nor inhibition of rotamase activity of FKBP alone is sufficient to explain the biologic actions of these drugs. Rather, these findings suggest that immunophilin bound to FK506 interferes with antigen receptor-induced signals, while rapamycin bound to the immunophilin interferes with IL-2-induced signals.

The effect of unilateral corneal anesthesia on the Schirmer test

Unilateral corneal anesthesia (or hypesthesia) caused by trigeminal nerve disease has an unknown effect on the Schirmer test. Using topical anesthesia, we found that unilateral corneal anesthesia reduces tearing bilaterally, with a greater decrease on the anesthetized side. Clinicians should be aware that trigeminal nerve deficit may alter Schirmer test results, and use bilateral topical corneal anesthesia or alternative methods to stimulate tearing in these cases.