M. Braun (Biology ’11), M. Menges (Biology '10), F. Opoku  (Biochemistry ’13) and A. M. Smith.  2013. The relative contribution of calcium, zinc and oxidation-based cross-links to the stiffness of Arion subfuscus glue. The Journal of Experimental Biology 216, 1475-148.  View the article here.

Metal ions are present in many different biological materials, and are capable of forming strong cross-links in aqueous environments. The relative contribution of different metal-based cross-links was measured in the defensive glue produced by the terrestrial slug Arion subfuscus. This glue contains calcium, zinc, manganese, iron and copper. These metals are essential to the integrity of the glue and to gel stiffening. Removal of all metals caused at least a fifteen-fold decrease in the storage modulus of the glue. Selectively disrupting cross-links involving hard Lewis acids such as calcium weakened the glue, while disrupting cross-links involving borderline Lewis acids such as zinc did not. Calcium is the most common cation bound to the glue (40 mmol L^-1), and its charge is balanced primarily by sulfate at 82 to 84 mmol L^-1. Thus, these ions likely play a primary role in bringing polymers together directly. Imine bonds formed as a result of protein oxidation also contribute substantially to the strength of the glue. Disrupting these bonds with hydroxylamine caused a 33% decrease in storage modulus of the glue, while stabilizing them by reduction with sodium borohydride increased the storage modulus by 40%. Thus, a combination of metal-based bonds operates in this glue. Most likely, cross-links directly involving calcium play a primary role in bringing together and stabilizing the polymer network, followed by imine bond formation and possible iron coordination.

Lyndaker, A.M., et, al. "Conditional Inactivation of the DNA Damage Response Gene Hus1 in Mouse Testis Reveals Separable Roles for Components of the RAD9-RAD1-HUS1 Complex in Meiotic Chromosome Maintenance."  PLoS Genetics, 9(2): e1003320. doi:10.1371/journal.pgen.1003320.  View the article here.

The RAD9-RAD1-HUS1 (9-1-1) complex is a heterotrimeric PCNA-like clamp that responds to DNA damage in somatic cells by promoting DNA repair as well as ATR-dependent DNA damage checkpoint signaling. In yeast, worms, and flies, the 9-1-1 complex is also required for meiotic checkpoint function and efficient completion of meiotic recombination; however, since Rad9, Rad1, and Hus1 are essential genes in mammals, little is known about their functions in mammalian germ cells. In this study, we assessed the meiotic functions of 9-1-1 by analyzing mice with germ cell-specific deletion of Hus1 as well as by examining the localization of RAD9 and RAD1 on meiotic chromosomes during prophase I. Hus1 loss in testicular germ cells resulted in meiotic defects, germ cell depletion, and severely compromised fertility. Hus1-deficient primary spermatocytes exhibited persistent autosomal γH2AX and RAD51 staining indicative of unrepaired meiotic DSBs, synapsis defects, an extended XY body domain often encompassing partial or whole autosomes, and an increase in structural chromosome abnormalities such as end-to-end X chromosome-autosome fusions and ruptures in the synaptonemal complex. Most of these aberrations persisted in diplotene-stage spermatocytes. Consistent with a role for the 9-1-1 complex in meiotic DSB repair, RAD9 localized to punctate, RAD51-containing foci on meiotic chromosomes in a Hus1-dependent manner. Interestingly, RAD1 had a broader distribution that only partially overlapped with RAD9, and localization of both RAD1 and the ATR activator TOPBP1 to the XY body and to unsynapsed autosomes was intact in Hus1 conditional knockouts. We conclude that mammalian HUS1 acts as a component of the canonical 9-1-1 complex during meiotic prophase I to promote DSB repair and further propose that RAD1 and TOPBP1 respond to unsynapsed chromatin through an alternative mechanism that does not require RAD9 or HUS1.

Spring 2013

Merriam, L.A, Baran, C.N. ('08), Girard, B., Hardwick, J.C., May, V., and Parsons, R.L. (2013). PAC1 receptor internalization and endosomal signaling mediate the PACAP-induced increase in guinea pig neuron excitability.  Journal of Neuroscience, 6 March 2013, 33(10): 4614-4622.  View the article.

Fall 2012

Jean C. Hardwick, E. Marie Southerland, Allison E. Girasole ('10), Shannon E. Ryan ('12), Sara Negrotto, and Jeffrey L. Ardell. Remodeling of intrinsic cardiac neurons: effects of β-adrenergic receptor blockade in guinea pig models of chronic heart disease. Am J Physiol Regul Integr Comp Physiol. 2012 Nov;303(9):R950-8. doi: 10.1152/ajpregu.00223.2012. Epub 2012 Aug 29.  View the abstract here.

Peter J. Melcher, N. Michele Holbrook, Michael J. Burns, Maciej A. Zwieniecki, Alexander R. Cobb, Timothy J. Brodribb, Brendan Choat and Lawren Sack. 2012. "Measurements of stem xylem hydraulic conductivity in the laboratory and field". Methods in Ecology and Evolution. 3:685-694. 

Michael Kerchner, Jean C. Hardwick, and Janice E. Thornton. “Identifying and Using ‘Core Competencies’ to Help Design and Assess Undergraduate Neuroscience Curricula”. The Journal of Undergraduate Neuroscience Education (JUNE), Fall 2012, 11(1):A27-A37. View the PDF here.