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Goff R.P.,Minneapolis | Bersie S.M.,Cell Biology and Development | Iaizzo P.A.,Minneapolis | Iaizzo P.A.,University of Minnesota
Heart Rhythm | Year: 2014

Background Phrenic nerve injury, both left and right, is considered a significant complication of cryoballoon ablation for treatment of drug-refractory atrial fibrillation, and functional recovery of the phrenic nerve can take anywhere from hours to months. Objective The purpose of this study was to focus on short periods of cooling to determine the minimal amount of cooling that may terminate nerve function related to cryo ablation. Methods Left and/or right phrenic nerves were dissected from the pericardium and connective tissue of swine (n = 35 preparations). Nerves were placed in a recording chamber modified with a thermocouple array. This apparatus was placed in a digital water bath to maintain an internal chamber temperature of 37°C. Nerves were stimulated proximally with a 1-V, 0.1-ms square wave. Bipolar compound action potentials were recorded proximal and distal to the site of ablation both before and after ablation, then analyzed to determine changes in latency, amplitude, and duration. Temperatures were recorded at a rate of 5 Hz, and maximum cooling rates were calculated. Results Phrenic nerves were found to elicit compound action potentials upon stimulation for periods up to 4 hours minimum. Average conduction velocity was 56.7 ± 14.7 m/s preablation and 49.8 ± 16.6 m/s postablation (P =.17). Cooling to mild subzero temperatures ceased production of action potentials for >1 hour. Conclusion Taking into account the data presented here, previous publications, and a conservative stance, during cryotherapy applications, cooling of the nerve to below 4°C should be avoided whenever possible. © 2014 Heart Rhythm Society. Source

Jo J.,Laboratory of Biological Modeling | Ahlgren U.,Umea Center for Molecular Medicine | Sorenson R.,Cell Biology and Development | Periwal V.,Laboratory of Biological Modeling
Islets | Year: 2012

The islets of Langerhans, ranging in size from clusters of a few cells to several thousand cells, are scattered near large blood vessels. While the β-cell mass in mammals is proportional to body weight, the size ranges of islets are similar between species with different body sizes, possibly reflecting an optimal functional size. The large range of islet sizes suggests a stochastic developmental process. It is not fully understood how islets develop to reach such size distributions, and how their sizes change under certain physiological and pathological conditions such as development, pregnancy, aging, obesity, and diabetes. The lack of a high-resolution in vivo imaging technique for pancreatic islets implies that the only data available to elucidate the dynamics of islet development are cross-sectional quantifications of islet size distributions. In this review, we infer biological processes affecting islet morphology in the large by examining changes of islet size distributions. Neonatal islet formation and growth is shown as a particular example of developing a mathematical model of islet size distribution. Application of this modeling to elucidate islet changes under other conditions is also discussed. Source

Billington C.J.,University of Minnesota | Ng B.,University of Minnesota | Forsman C.,University of Minnesota | Schmidt B.,University of Minnesota | And 6 more authors.
Developmental Biology | Year: 2011

The severity of numerous developmental abnormalities can vary widely despite shared genetic causes. Mice deficient in Twisted gastrulation (Twsg1-/-) display such phenotypic variation, developing a wide range of craniofacial malformations on an isogenic C57BL/6 strain background. To examine the molecular basis for this reduced penetrance and variable expressivity, we used exon microarrays to analyze gene expression in mandibular arches from several distinct, morphologically defined classes of Twsg1-/- and wild type (WT) embryos. Hierarchical clustering analysis of transcript levels identified numerous differentially expressed genes, clearly distinguishing severely affected and unaffected Twsg1-/- mutants from WT embryos. Several genes that play well-known roles in craniofacial development were upregulated in unaffected Twsg1-/- mutant embryos, suggesting that they may compensate for the loss of TWSG1. Imprinted genes were overrepresented among genes that were differentially expressed particularly between affected and unaffected mutants. The most severely affected embryos demonstrated increased p53 signaling and increased expression of its target, Trp53inp1. The frequency of craniofacial defects significantly decreased with a reduction of p53 gene dosage from 44% in Twsg1-/-p53+/+ pups (N=675) to 30% in Twsg1-/-p53+/- (N=47, p=0.04) and 15% in Twsg1-/-p53-/- littermates (N=39, p=0.001). In summary, these results demonstrate that phenotypic variability in Twsg1-/- mice is associated with differential expression of certain developmentally regulated genes, and that craniofacial defects can be partially rescued by reduced p53 levels. We postulate that variable responses to stress may contribute to variable craniofacial phenotypes by triggering differential expression of genes and variable cellular apoptosis. © 2011 Elsevier Inc. Source

Ou L.,Cell Biology and Development | Herzog T.L.,Molecular Biology and Biophysics | Herzog T.L.,University of Minnesota | Wilmot C.M.,University of Minnesota | Whitley C.B.,Molecular
Molecular Genetics and Metabolism | Year: 2014

The lack of methodological uniformity in enzyme assays has been a long-standing difficulty, a problem for bench researchers, for the interpretation of clinical diagnostic tests, and an issue for investigational drug review. Illustrative of the problem, α-L-iduronidase enzyme catalytic activity is frequently measured with the substrate 4-methylumbelliferyl-α-L-iduronide (4MU-iduronide); however, final substrate concentrations used in different assays vary greatly, ranging from 25μM to 1425μM (Km≈180μM) making it difficult to compare results between laboratories. In this study, α-L-iduronidase was assayed with 15 different substrate concentrations. The resulting activity levels from the same specimens varied greatly with different substrate concentrations but, as a group, obeyed the expectations of Michaelis-Menten kinetics. Therefore, for the sake of improved comparability, it is proposed that α-L-iduronidase enzyme assays should be conducted either (1) under substrate saturating conditions; or (2) when concentrations are significantly below substrate saturation, with results standardized by arithmetic adjustment that considers Michaelis-Menten kinetics. The approach can be generalized to many other enzyme assays. © 2013 Elsevier Inc. Source

News Article
Site: http://phys.org/biology-news/

Now, researchers at The Rockefeller University have identified a new mechanism by which cells are instructed during development to become stem cells. The results, published in Cell on January 14, help explain how communication between cells mediates this process, and may have implications for skin cancer treatments. "While adult stem cells are increasingly well-characterized, we know little about their origins. Here, we show that in the skin, stem cell progenitors of the hair follicle are specified as soon as the cells within the single-layered embryonic epidermis begin to divide downward to form an embryonic hair bud," explains Elaine Fuchs, Robin Chemers Neustein Laboratory of Mammalian Cell Biology and Development. "This timing was much earlier than previously thought, and gives us new insights into the establishment of these very special cells." Which came first, the stem cell or the niche? Clusters of stem cells receive signals from other nearby cells that instruct them to either stay a stem cell, or differentiate into a specific cell type. These instructive groups of cells, called the "niche," are known to maintain adult stem cell populations. Less well understood is how the niche forms, or when and where stem cells first appear during embryonic development. "Adult stem cells are dependent on the niche for instructions on both how to become a stem cell, and how to control stem cell population size," says first author Tamara Ouspenskaia. "The question was, does the niche appear first and call other cells over to become stem cells? Or is it the other way around? Stem cells could be appearing elsewhere first and then recruiting the niche." Working in the mouse hair follicle, a region that contains active stem cells, Fuchs and colleagues investigated the cell divisions that occur as a hair follicle is first forming. The hair follicle begins as a small bud called a placode, and develops into a tissue of multiple layers, comprised of different cell types. By labeling cells within the placode and tracing their progeny, the researchers determined that from each division, one daughter cell stayed put, while the other escaped to a different layer. Further experiments revealed that this escapee becomes a stem cell. This finding is significant as it's the earliest point in development that stem cells have been detected in this system, and it indicates stem cells may exist before the niche is formed. Flying the nest to become a stem cell How cells become the cell type they're destined to be—a liver cell or skin cell, for example—depends on a number of factors, including molecular signals from other cells that help turn specific genes on or off. Fuchs and colleagues observed that the signaling activity was different between the two daughter cells that ended up in different locations, and aimed to characterize how signaling helped seal their ultimate cell fate. They found that the environment to which the escapee cell daughter moved had low levels of WNT signaling, known to play a role in embryonic development. In contrast, WNT signaling was high in the environment where the other daughter remained. The level of WNT affected how the cells responded to another signal known as SHH (Sonic Hedgehog)—only those in the low-WNT environment responded to SHH signaling, which instructed the cells to become stem cells. "These cells must leave home, they must leave the environment with high WNT signaling, to become stem cells," says Ouspenskaia. "We observed that SHH, which actually comes from the cells with high WNT signaling, is essential in helping the cells leave. So in order for this escapee cell to become a stem cell, it needs to receive an SHH signal from its sister cell at home telling it 'you're the stem cell.'" The researchers believe that antagonism between WNT and SHH signaling may help to control the number of stem cells produced during this time of embryo development. "This newly identified signaling crosstalk provides insights into why these two signals have such a profound impact on skin cancers, where the numbers of cancerous tissue-propagating stem cells are excessive," says Fuchs, who is also a Howard Hughes Medical Institute investigator. "This work now paves the way for future research into the fascinating and clinically important relation between tumor-propagating and normal stem cells." Explore further: Tiny hair follicle offers big clues about the life and death of stem cells More information: WNT-SHH Antagonism Specifies and Expands Stem Cells prior to Niche Formation , Cell 164, 156–169. DOI: 10.1016/j.cell.2015.11.058 , http://www.cell.com/cell/abstract/S0092-8674(15)01577-9

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