Control of stem cell fate by engineering their micro and nanoenvironment

Stem cells are capable of long-term self-renewal and differentiation into specialised cell types, making them an ideal candidate for a cell source for regenerative medicine. The control of stem cell fate has become a major area of interest in the field of regenerative medicine and therapeutic intervention. Conventional methods of chemically inducing stem cells into specific lineages is being challenged by the advances in biomaterial technology, with evidence highlighting that material properties are capable of driving stem cell fate. Materials are being designed to mimic the clues stem cells receive in their in vivo stem cell niche including topographical and chemical instructions. Nanotopographical clues that mimic the extracellular matrix(ECM) in vivo have shown to regulate stem cell differentiation. The delivery of ECM components on biomaterials in the form of short peptides sequences has also proved successful in directing stem cell lineage. Growth factors responsible for controlling stem cell fate in vivo have also been delivered via biomaterials to provide clues to determine stem cell differentiation. An alternative approach to guide stem cells fate is to provide genetic clues including delivering DNA plasmids and small interfering RNAs via scaffolds. This review, aims to provide an overview of the topographical, chemical and molecular clues that biomaterials can provide to guide stem cell fate. The promising features and challenges of such approaches will be highlighted, to provide directions for future advancements in this exciting area of stem cell translation for regenerative medicine.     

In vivo Biosynthesis of isopentenylacetophenones in Eupatorium rugosum

The biosynthesis of dehydrotremetone in Eupatorium rugosum has been investigated by feeding radioactive precursors to intact plants. The carbon atoms of acetate-[1-¹⁴C] and acetate-[2-¹⁴C] were identified in dehydrotremetone by degradation of the molecule. From the pattern of labeling it was concluded that the acetophenone moiety was derived from acetate via the polyacetate pathway. From the incorporation of mevalonate it appeared that the furan ring and its side chain were formed from an isoprenoid compound. Potential aromatic intermediates were chemically synthesized and also fed to plants but only tremetone was found to be efficiently incorporated into dehydrotremetone. Neither 4-hydroxyacetophenone nor 4-hydroxy-3[isopenten-(2)-yl]-acetophenone were efficiently incorporated into dehydrotremetone.     

Genetic covariance between indices of body condition and immunocompetence in a passerine bird

Background  

Condition-dependence is a ubiquitous feature of animal life histories and has important implications for both natural and sexual selection. Mate choice, for instance, is typically based on condition-dependent signals. Theory predicts that one reason why condition-dependent signals may be special is that they allow females to scan for genes that confer high parasite resistance. Such explanations require a genetic link between immunocompetence and body condition, but existing evidence is limited to phenotypic associations. It remains unknown, therefore, whether females selecting males with good body condition simply obtain a healthy mate, or if they acquire genes for their offspring that confer high immunocompetence.     

Mediation of pinocytosis in cultured arterial smooth muscle and endothelial cells by platelet-derived growth factor

Pinocytosis was measured in monkey aortic smooth muscle cells (SMC), bovine aortic endothelial cells, and Swiss 3T3 cells in culture as cellular uptake of [U-(14)C]sucrose and horseradish peroxidase (HRP) from the tissue culture medium. Monkey arterial SMC and Swiss 3T3 cells were maintained in a quiescent state of growth at low cells density in medium containing 5 percent monkey plasma-derived serum (PDS). Replacement of PDS with 5 percent monkey whole blood serum (WBS) from the same donor, or addition to PDS of partially purified platelet-derived growth factor(s) (PF), resulted in a marked stimulation of pinocytosis as well as of cellular proliferation. In SMC, enhancement of the rate of pinocytosis occurred 4-6 h after exposure to WBS or PF, and the rate was up to twofold higher than the rate in medium containing PDS. In contrast, [(3)H]thymidine uptake by SMC did not increase until 12-16 h after exposure to PF. In endothelial cells the presence of PF or WBS did not enhance either the rate of pinocytosis or the rate of proliferation over that in PDS. Thus, endothelial cells did not become quiescent at subconfluent densities in PDS but maintained rates of proliferation and pinocytosis that were equivalent to those in WBS. By autoradiography, the fraction of labeled nuclei in SMC cultures 24 h after change of medium increased from 0.061 +/- 0.004 in quiescent cultures to 0.313 +/- 0.028 after exposure to WBS or PF. In contrast, labeling indices of endothelial cells were similar for cultures grown in PDS, WBS, or PF at any single time point after change of medium. These findings suggest that the rate of pinocytosis maybe be coupled in some fashion to growth regulation, which may be mediated in part by specific growth factors, such as that derived from the thrombocyte.     

Cyclic modulation of enzymes of pyrimidine nucleotide biosynthesis precedes sialoglycoconjugate changes during 2-acetylaminofluorene-induced hepatocarcinogenesis in the rat

Three enzymatic activities associated with pyrimidine nucleotide biosynthesis were monitored at weekly or bi-weekly intervals during 2-acetylaminofluorene- (0.025% in a Farber Basal Carcinogenic diet) induced hepatocarcinogenesis in the rat. Dihydroorotate dehydrogenase, the fourth of six enzymes in de novo pyrimidine biosynthesis, declined in activity while UDP kinase and CTP synthetase showed sequential increases in activity. The alterations in activity appeared to be cyclic, followed by a full or partial return to control values. Three full cycles were monitored. The first cycle preceded nodule formation. The second cycle accompanied nodule formation and preceded sialoglycoconjugate changes reported previously. The third cycle accompanied the early glycoconjugate changes. The cyclic pattern was reproducible in three separate experiments. In each cycle, the order of events was as follows: decrease in dihydroorotate dehydrogenase, sequential increases in UDP kinase, CTP synthetase and CMPsialic acid synthase, and finally increases in the enzyme lactosylceramide: CMPsialic acid sialyltransferase, lipid-soluble sialic acid and total sialic acid. In livers of animals fed 1.87% of the hepatotoxin, 4-acetamidophenol, no biochemical alterations resembling those induced by 2-acetylaminofluorene were obtained, despite acute centrilobular necrosis of the livers. The findings point to a biochemical cascade beginning with administration of carcinogen and continuing through the development of hyperplastic nodules and of frank carcinomas resulting not from hepatotoxicity but as events associated with the hepatocarcinogenic progression.     

Purification and properties of dimethylallylpyrophosphate: Tryptophan dimethylallyl transferase,the first enzyme of ergot alkaloid biosynthesis in Claviceps. sp. SD 58

Dimethylallylpyrophosphate:l-tryptophan dimethylallyltransferase (DMAT synthetase), the first pathway-specific enzyme of ergot alkaloid biosynthesis, has been isolated from mycelia of Claviceps sp., strain SD 58, and purified to apparent homogeneity. The enzyme reaction products were identified as l-4-(γ,γ-dimethylallyl)tryptophan and inorganic pyrophosphate. DMAT synthetase is a single subunit protein of molecular weight 70,000–73,000 and has an isoelectric point at pH 5.8. The enzyme is activated by Fe²⁺, Mg²⁺, and particularly Ca²⁺; K_m values for l-tryptophan and dimethylallylpyrophosphate were determined to be 0.067 and 0.2 mm, respectively. Kinetic analysis indicated that the DMAT synthetase reaction proceeds by a sequential rather than a ping-pong mechanism.