Cellular mechanisms of intestine regeneration in the sea cucumber, Holothuria glaberrima Selenka (Holothuroidea:Echinodermata)

Echinoderms are the deuterostome group with the most striking capacity to regenerate lost body parts. In particular, members of the class Holothuroidea are able to regenerate most of their internal organs following a typical evisceration process. Such formation of new viscera in an adult organism provides a unique model to study the process of organogenesis. We have studied this process in the sea cucumber Holothuria glabberrima by describing the spatial and temporal pattern of cellular events that occur during intestine regeneration following chemically induced evisceration. Regeneration begins as a thickening of the mesenteries that supported the autotomized organs to the body wall. The mesenterial thickening consists of tissues where most of the cellular populations found in the normal intestine are already present. However, the cell numbers differ, particularly those of hemocytes and amoebocytes, suggesting that some of these cells play an important role in the formation of the solid rod of hypertrophic mesentery that characterizes the intestinal primordia. The appearance of the luminal epithelium, together with the formation of the lumen, occurs during the second week of regeneration by proliferation and extensive migration of cells from the esophagus and cloacal ends into the thickenings. At this stage all tissue layers are present, but it takes an additional week for them to exhibit the proportions typical of the normal organ. Cell division, as determined by BrdU labeling, mainly occurs in the coelomic epithelia of the hypertrophic mesentery and in the regenerating luminal epithelium. Our study provides evidence that the process of new organ formation in holothurians can be described as an intermediate process showing characteristics of both epimorphic and morphallactic phenomena.     

Seminar planning guidelines. As I see it

Small local chapter groups can present quality cost effective regional seminars. Key components are dedication of members, teamwork, and a sense of direction. The following guidelines and information can provide a framework for planning and coordinating a seminar.     

The X-linked lymphoproliferative-disease gene product SAP regulates signals induced through the co-receptor SLAM

In addition to triggering the activation of B- or T-cell antigen receptors, the binding of a ligand to its receptor at the cell surface can sometimes determine the physiological outcome of interactions between antigen-presenting cells, T and B lymphocytes. The protein SLAM (also known as CDw150), which is present on the surface of B and T cells, forms such a receptor-ligand pair as it is a self-ligand. We now show that a T-cell-specific, SLAM-associated protein (SAP), which contains an SH2 domain and a short tall, acts as an inhibitor by blocking recruitment of the SH2-domain-containing signal-transduction molecule SHP-2 to a docking site in the SLAM cytoplasmic region. The gene encoding SAP maps to the same area of the X chromosome as the locus for X-linked lymphoproliferative disease (XLP) and we found mutations in the SAP gene in three XLP patients. Absence of the inhibitor SAP in XLP patients affects T/B-cell interactions induced by SLAM, leading to an inability to control B-cell proliferation caused by Epstein-Barr virus infections.     

A mutation spectra database for bacterial and mammalian genes: 1998

This database consists of over 24 000 mutations in 18 viral, bacterial, yeast or mammalian genes. The data are grouped as sets of DNA base sequence changes or spectra caused by a particular mutagen under defined conditions. The spectra are available on the World Wide Web at http://info.med.yale.edu/mutbase/ in two formats; in text format that can be browsed on-line or downloaded for use with a text editor and in dBASEIII format for use, after downloading, by relational database programs or by spreadsheets. Researchers are encouraged to submit DNA sequence changes to a suitable mutation database such as ours. A data entry program, MUTSIN, can be retrieved from this site. MUTSIN diagrams each mutation on the computer screen and alerts the user to any discrepancies.     

NMDA receptors mediate peripheral chemoreceptor afferent input in the conscious rat

N-methyl-D-aspartate (NMDA) glutamate receptors mediate critical components of cardiorespiratory control in anesthetized animals. The role of NMDA receptors in the ventilatory responses to peripheral and central chemoreceptor stimulation was investigated in conscious, freely behaving rats. Minute ventilation (VE) responses to 10% O2, 5% CO2, and increasing intravenous doses of sodium cyanide were measured in intact rats before and after intravenous administration of the NMDA receptor antagonist MK-801 (3 mg/kg). After MK-801, eupcapnic tidal volume (VT) decreased while frequency increased, resulting in a modest reduction in VE. Inspiratory time (TI) decreased, whereas expiratory time remained unchanged. The VE responses to hypercapnia were qualitatively similar in control and MK-801 conditions, with slight reductions in respiratory drive (VT/TI) after MK-801. In contrast, responses to hypoxia were markedly attenuated after MK-801 and were primarily due to reduced frequency changes, whereas VT was unaffected. Sodium cyanide doses associated with significant VE increases were 5 and 50 microg/kg before and after MK-801, respectively. Thus 1-log shift to the right of individual dose-response curves occurred with MK-801. Selective carotid body denervation reduced VE during hypoxia by 70%, and residual hypoxic ventilatory responses were abolished after MK-801. These findings suggest that, in conscious rats, carotid and other peripheral chemoreceptor-mediated hypoxic ventilatory responses are critically dependent on NMDA receptor activation and that NMDA receptor mechanisms are only modestly involved during hypercapnia.     

Microstructure and fracture behaviour of short and long fibre-reinforced polypropylene composites

Microstructure and fracture mechanical behaviour of injection-moulded, longer glass fibrereinforced polypropylene (Verton* aspect ratio 320) were studied as a function of fibre volume fraction and compared to that of shorter fibre-filled polypropylene (aspect ratio 70). Toughness was measured using instrumented notched lzod and falling weight impact tests, as well as compact tension specimens. It was found that the addition of longer fibres generally increased the toughness of the material, although more significant increases were seen in the impact tests than were seen in the compact tension test. For the latter results, a correlation between toughness improvement and microstructural details was performed on the basis of the microstructural efficiency concept, a semi-empirical approach of the formK _c,C = (a* +nR)K _c,M, where,K _c,C andK _c,M are the fracture toughnesses of the composite and the matrix, respectively,_a* is a matrix stress correction factor,n is a scaling parameter andR is a fibre reinforcement effectiveness factor. The latter corrects for differences in the composite microstructures, and incorporates effective fibre orientation factors, layering of injection moulded parts, and fibre volumes in the different layers.Nomenclature a crack length - a ^* matrix toughness correction factor - A cross-sectional area - B thickness of the sample plaques - C thickness of the composite core regions - E _peak energy adsorbed up to the maximum force in the impact load-displacement curve - E _t tensile modulus - F _max maximum force in impact force-displacement curves - f _p fibre orientation factor - f _pe effective orientation factor - f _pe,C effective orientation parameter, core region - f _{pe, s} effective orientation parameter, surface region - F critical load in the tensile test load-displacement curves - K _c critical stress intensity factor/fracture toughness - K _L fracture toughness of the composite materials - K _d dynamic fracture toughness - K _L fracture toughness of the matrix - L test with crack parallel to the mould filling direction - M microstructural efficiency factor - n scaling parameter for reinforcement effectiveness factor (energy absorbtion ratio) - R reinforcement effectiveness factor - S thickness of the composite surface regions - T test with crack perpendicular to the mould filling direction - V _f fibre volume fraction - V _m matrix volume fraction (= 1 —V _f) - W specimen width - W _f fibre weight fraction - W _m matrix weight fraction (= 1 —W _f) - X _n number average fibre length - X _v volume average fibre length - Y(a/ W) polynomial correction for compact tension specimens - variable in effective orientation factor formula - variable in effective orientation factor formula - _B strain to break - _c density of the composite - _f fibre density - _m matrix density - _F fracture strength - fibre angle with respect to a reference direction     

The Complex and Critical Role of Glycine 12 (G12) in Beta-Connexins of Human Skin

Glycine is an amino acid with unique properties because its side chain is composed of a single hydrogen atom. It confers conformational flexibility to proteins and conserved glycines are often indicative of protein domains involving tight turns or bends. All six beta-type connexins expressed in human epidermis (Cx26, Cx30, Cx30.3, Cx31, Cx31.1 and Cx32) contain a glycine at position 12 (G12). G12 is located about halfway through the cytoplasmic amino terminus and substitutions alter connexin function in a variety of ways, in some cases altering protein interactions and leading to cell death. There is also evidence that alteration of G12 changes the structure of the amino terminus in connexin- and amino acid- specific ways. This review integrates structural, functional and physiological information about the role of G12 in connexins, focusing on beta-connexins expressed in human epidermis. The importance of G12 substitutions in these beta-connexins is revealed in two hereditary skin disorders, keratitis ichthyosis and erythrokeratodermia variabilis, both of which result from missense mutations affecting G12.     

The reaction of 1,2-dichloroethane with copper

The decomposition of 1,2-dichloroethane on polycrystalline copper has been studied using a microreactor. The reaction is found to have an activation energy of 81±5 kJ mol^–1 generating gaseous ethene and chemisorbed chlorine. The reaction terminates on completion of a monolayer of chemisorbed chlorine and is followed by a much slower reaction. The rate limiting step is thought to be C₂H₄Cl_2(phys)C2H₄Cl(_ads)+Cl_ads The reaction is compared with a UHV study of the same molecule on Cu(l 11) and the possibility of a negative ion transition state is discussed.     

Induced chemical shifts in the NMR spectrum of methyl petroselinate

The use of a pseudo contact shift reagent, (Eu[fod]₃), to obtain simplified NMR spectra of a typical long chain monounsaturated fatty acid methyl ester, methyl petroselinate, is described. Spectra were obtained in which individual methylene groups are identifiable from their splitting patterns. Non-equivalent splitting patterns were observed for the methine protons with varying amounts of reagent used. The effect of concentration of the shift reagent on the chemical shift is discussed. Presented in part at the Meeting of the Gulf Coast Instrumental Analysis Group, Houston, October 1971. S. Market. and Nutr. Res. Div., ARS, USDA