Substrate elasticity provides mechanical signals for the expansion of hemopoietic stem and progenitor cells

Surprisingly little is known about the effects of the physical microenvironment on hemopoietic stem and progenitor cells. To explore the physical effects of matrix elasticity on well-characterized primitive hemopoietic cells, we made use of a uniquely elastic biomaterial, tropoelastin. Culturing mouse or human hemopoietic cells on a tropoelastin substrate led to a two- to threefold expansion of undifferentiated cells, including progenitors and mouse stem cells. Treatment with cytokines in the presence of tropoelastin had an additive effect on this expansion. These biological effects required substrate elasticity, as neither truncated nor cross-linked tropoelastin reproduced the phenomenon, and inhibition of mechanotransduction abrogated the effects. Our data suggest that substrate elasticity and tensegrity are important mechanisms influencing hemopoietic stem and progenitor cell subsets and could be exploited to facilitate cell culture.     

The role of DNA methylation,nucleosome occupancy and histone modifications in paramutation

Paramutation is the transfer of epigenetic information between alleles that leads to a heritable change in expression of one of these alleles. Paramutation at the tissue‐specifically expressed maize (Zea mays) b1 locus involves the low‐expressing B′ and high‐expressing B‐I allele. Combined in the same nucleus, B′ heritably changes B‐I into B′. A hepta‐repeat located 100‐kb upstream of the b1 coding region is required for paramutation and for high b1 expression. The role of epigenetic modifications in paramutation is currently not well understood. In this study, we show that the B′ hepta‐repeat is DNA‐hypermethylated in all tissues analyzed. Importantly, combining B′ and B‐I in one nucleus results in de novo methylation of the B‐I repeats early in plant development. These findings indicate a role for hepta‐repeat DNA methylation in the establishment and maintenance of the silenced B′ state. In contrast, nucleosome occupancy, H3 acetylation, and H3K9 and H3K27 methylation are mainly involved in tissue‐specific regulation of the hepta‐repeat. Nucleosome depletion and H3 acetylation are tissue‐specifically regulated at the B‐I hepta‐repeat and associated with enhancement of b1 expression. H3K9 and H3K27 methylation are tissue‐specifically localized at the B′ hepta‐repeat and reinforce the silenced B′ chromatin state. The B′ coding region is H3K27 dimethylated in all tissues analyzed, indicating a role in the maintenance of the silenced B′ state. Taken together, these findings provide insight into the mechanisms underlying paramutation and tissue‐specific regulation of b1 at the level of chromatin structure.     

Fibulin-5 binds human smooth-muscle cells through alpha5beta1 and alpha4beta1 integrins, but does not support receptor activation

Fibulin-5, an extracellular matrix glycoprotein expressed in elastin-rich tissues, regulates vascular cell behaviour and elastic fibre deposition. Recombinant full-length human fibulin-5 supported primary human aortic SMC (smooth-muscle cell) attachment through alpha5beta1 and alpha4beta1 integrins. Cells on fibulin-5 spread poorly and displayed prominent membrane ruffles but no stress fibres or focal adhesions, unlike cells on fibronectin that also binds these integrins. Cell migration and proliferation were significantly lower on fibulin-5 than on fibronectin. Treatment of cells on fibulin-5 with a beta1 integrin-activating antibody induced stress fibres, increased attachment, migration and proliferation, and stimulated signalling of epidermal growth factor receptor and platelet-derived growth factor receptors alpha and beta. Fibulin-5 also modulated fibronectin-mediated cell spreading and morphology. We have thus identified the beta1 integrins on primary SMCs that fibulin-5 interacts with, and have shown that failure of fibulin-5 to activate these receptors limits cell spreading, migration and proliferation.     

Safeguarding marine life: conservation of biodiversity and ecosystems

Reviews in Fish Biology and Fisheries - Marine ecosystems and their associated biodiversity sustain life on Earth and hold intrinsic value. Critical marine ecosystem services include maintenance of...     

Ocean resource use: building the coastal blue economy

Reviews in Fish Biology and Fisheries - Humans have relied on coastal resources for centuries. However, current growth in population and increased accessibility of coastal resources through...     

A Novel MHC-I Surface Targeted for Binding by the MCMV m06 Immunoevasin Revealed by Solution NMR

As part of its strategy to evade detection by the host immune system, murine cytomegalovirus (MCMV) encodes three proteins that modulate cell surface expression of major histocompatibility complex class I (MHC-I) molecules: the MHC-I homolog m152/gp40 as well as the m02-m16 family members m04/gp34 and m06/gp48. Previous studies of the m04 protein revealed a divergent Ig-like fold that is unique to immunoevasins of the m02-m16 family. Here, we engineer and characterize recombinant m06 and investigate its interactions with full-length and truncated forms of the MHC-I molecule H2-L^d by several techniques. Furthermore, we employ solution NMR to map the interaction footprint of the m06 protein on MHC-I, taking advantage of a truncated H2-L^d, “mini-H2-L^d,” consisting of only the α1α2 platform domain. Mini-H2-L^d refolded in vitro with a high affinity peptide yields a molecule that shows outstanding NMR spectral features, permitting complete backbone assignments. These NMR-based studies reveal that m06 binds tightly to a discrete site located under the peptide-binding platform that partially overlaps with the β₂-microglobulin interface on the MHC-I heavy chain, consistent with in vitro binding experiments showing significantly reduced complex formation between m06 and β₂-microglobulin-associated MHC-I. Moreover, we carry out NMR relaxation experiments to characterize the picosecond-nanosecond dynamics of the free mini-H2-L^d MHC-I molecule, revealing that the site of interaction is highly ordered. This study provides insight into the mechanism of the interaction of m06 with MHC-I, suggesting a structural manipulation of the target MHC-I molecule at an early stage of the peptide-loading pathway.