抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Minimal criteria for defining multipotent mesenchymal stromal cells. The International Society for Cellular Therapy position statement

Stem cell biology has come of age. Unequivocal proof that stem cells exist in the haematopoietic system has given way to the prospective isolation of several tissue-specific stem and progenitor cells, the initial delineation of their properties and expressed genetic programmes, and the beginnings of their utility in regenerative medicine. Perhaps the most important and useful property of stem cells is that of self-renewal. Through this property, striking parallels can be found between stem cells and cancer cells: tumours may often originate from the transformation of normal stem cells, similar signalling pathways may regulate self-renewal in stem cells and cancer cells, and cancer cells may include 'cancer stem cells' - rare cells with indefinite potential for self-renewal that drive tumorigenesis.

/pdf/stem-cells-cancer-and-cancer-stem-cells-3s9b9ssybc.pdf

Stem cells, cancer, and cancer stem cells

Future cell-based therapies such as tissue engineering will benefit from a source of autologous pluripotent stem cells. For mesodermal tissue engineering, one such source of cells is the bone marrow stroma. The bone marrow compartment contains several cell populations, including mesenchymal stem cells (MSCs) that are capable of differentiating into adipogenic, osteogenic, chondrogenic, and myogenic cells. However, autologous bone marrow procurement has potential limitations. An alternate source of autologous adult stem cells that is obtainable in large quantities, under local anesthesia, with minimal discomfort would be advantageous. In this study, we determined if a population of stem cells could be isolated from human adipose tissue. Human adipose tissue, obtained by suction-assisted lipectomy (i.e., liposuction), was processed to obtain a fibroblast-like population of cells or a processed lipoaspirate (PLA). These PLA cells can be maintained in vitro for extended periods with stable population doubling and low levels of senescence. Immunofluorescence and flow cytometry show that the majority of PLA cells are of mesodermal or mesenchymal origin with low levels of contaminating pericytes, endothelial cells, and smooth muscle cells. Finally, PLA cells differentiate in vitro into adipogenic, chondrogenic, myogenic, and osteogenic cells in the presence of lineage-specific induction factors. In conclusion, the data support the hypothesis that a human lipoaspirate contains multipotent cells and may represent an alternative stem cell source to bone marrow-derived MSCs.

/pdf/multilineage-cells-from-human-adipose-tissue-implications-4z32vwpf0q.pdf

Multilineage cells from human adipose tissue: implications for cell-based therapies.

We report here that cells co-purifying with mesenchymal stem cells--termed here multipotent adult progenitor cells or MAPCs--differentiate, at the single cell level, not only into mesenchymal cells, but also cells with visceral mesoderm, neuroectoderm and endoderm characteristics in vitro. When injected into an early blastocyst, single MAPCs contribute to most, if not all, somatic cell types. On transplantation into a non-irradiated host, MAPCs engraft and differentiate to the haematopoietic lineage, in addition to the epithelium of liver, lung and gut. Engraftment in the haematopoietic system as well as the gastrointestinal tract is increased when MAPCs are transplanted in a minimally irradiated host. As MAPCs proliferate extensively without obvious senescence or loss of differentiation potential, they may be an ideal cell source for therapy of inherited or degenerative diseases.

/pdf/pluripotency-of-mesenchymal-stem-cells-derived-from-adult-200s4qlizf.pdf

Pluripotency of mesenchymal stem cells derived from adult marrow

Assay Optimization for the Objective Quantification of Human Multilineage Colony Forming Units.

Adult Stem Cell Plasticity

The Blood Vessels of Prometheus

The importance of National Blood Foundation funding.

Megakaryoblastic leukemia 1 (MKL1; also known as MRTFA, MAL, or BSAC) is a coactivator of serum response factor (SRF). SRF is a transcription factor that participates in the activation of immediate-early genes as well as genes associated with the cytoskeleton, proliferation, and apoptosis by binding promoter sequences known as serum response elements (SRE).1 The MKL1/SRF complex plays a critical role in megakaryocyte maturation.2,3 As megakaryocytes mature, they undergo successive rounds of endomitosis to become highly polyploid; Mkl1 knockout (KO) murine megakaryocytes exhibit reduced polyploidization, a phenotype that is more severe in double KO (dKO) megakaryocytes lacking both Mkl1 and the closely related Megakaryoblastic leukemia 2 (Mkl2, or Mrtfb).3,4 Additionally, MKL1 is part of the recurrent t(1;22) chromosomal translocation found in acute megakaryoblastic leukemia, which results in a fusion protein known as RBM15-MKL1.5 MKL1 and MKL2 each contain five highly conserved domains which have been investigated in the context of SRF coactivation using luciferase reporter assays.1,3,6,7 However, their functional effects in megakaryocyte polyploidization remain unknown, so structure-function analysis of these domains in primary megakaryocyte polyploidization is needed.7,8 Furthermore, the pro-tumorigenic mechanism of RBM15-MKL1 remains unclear, warranting further investigation of the individual proteins’ roles in both normal and pathological megakaryocyte development – particularly considering that all functional domains of MKL1 are retained in the fusion protein. In order to define which domains of MKL1 are necessary for polyploidization, we transduced wild-type (WT), Mkl1 KO and dKO murine bone marrow with domain-specific deletion constructs of MKL1, and analyzed subsequent megakaryocyte polyploidization. Published data have established that Mkl1 KO and dKO megakaryocytes have reduced polyploidization relative to WT cells in vivo. We expanded upon this by demonstrating reduced polyploidization of megakaryocytes differentiated in culture from hematopoietic stem and progenitor cells (HSPC).2,3,7 Murine bone marrow-derived HSPC were cultured for 48 hours in expansion medium (50 ng/mL murine Flt3, 20 ng/mL murine interleukin-3, 100 ng/mL murine stem cell factor, 50 ng/mL murine thrombopoietin in StemSpan [Stemcell Technologies]), then switched into megakaryocyte maturation medium (50 ng/mL murine thrombopoietin) for 4 days. Polyploidization was analyzed via flow cytometry using propidium iodide to visualize DNA content, and anti-CD41 to identify megakaryocytes. In order to capture the full spectrum of polyploidization, the mean fluorescence intensity (MFI) of propidium iodide was determined for each population. MFI was normalized to the WT value within each experiment to account for variations in fluorescence intensity between experiments and cytometers. Mkl1 KO and dKO megakaryocytes showed decreased MFI relative to WT, indicating a lower degree of polyploidization.2,3,7 This decrease was statistically significant for dKO cells (P=0.01, n=4). Mkl1 KO megakaryocytes exhibited a directional decrease in MFI which did not reach statistical significance (P=0.05, n=6) (Figure 1A). To test whether restoration of Mkl1 expression restores polyploidization, we overexpressed full-length (FL) MKL1 in WT, Mkl1 KO, and dKO megakaryocytes. We cloned FL MKL1 into a pMSCV-GW-RfA-PGK-EGFP retroviral backbone using vectors VB160922-1087ttu and VB1609221086xsa (VectorBuilder). Constructs were validated in HEL cells via western blot (Online Supplementary Figure S1A). Murine HSPC were cultured according to the above protocol, and transduced after 24 hours in expansion medium with 8 μg/mL polybrene via spinfection for 1 hour at 800 x g. The transduced megakaryocyte population was gated based on CD41/GFP fluorescence. Representative ploidy histograms are shown in Figure 1C and indicate that overexpression of FL MKL1 increases the number of high ploidy cells. Overexpression of MKL1 resulted in a statistically significant increase in polyploidization (as represented by the MFI of propidium iodide) of cells from each genotype (WT n=5, Mkl1 KO n=6, and dKO n=4), compared to empty vector controls (Figure 1B). Previous work has defined the roles of each domain in MKL1-mediated regulation of SRF in luciferase reporter assays.9 Two canonical N-terminal RPEL domains serve as negative regulators of MKL1/SRF by binding to G-actin, which promotes nuclear export;8,9,10 the Basic domain contains a nuclear localization signal and promotes dimerization of MKL1 with SRF;9,11 the LZ domain permits MKL1 heteroand homodimerization;1 and the C-terminal TAD domain is required for transcriptional activation of MKL1/SRF target genes.1 The SAP domain does not affect MKL1-induced luciferase reporter activity and has no clear role in MKL1 function.11 While SRF-independent functions have been reported for the SAP domain of MKL1, these findings have not been reproduced.12 We therefore tested

/pdf/structure-function-analysis-of-the-role-of-megakaryoblastic-12kfbioy.pdf

Diane S. Krause

Papers

Assay Optimization for the Objective Quantification of Human Multilineage Colony Forming Units.

Adult Stem Cell Plasticity

The Blood Vessels of Prometheus

The importance of National Blood Foundation funding.

Structure-function analysis of the role of megakaryoblastic leukemia 1 in megakaryocyte polyploidization