The interface between cell and developmental biology

ATP levels influence cell movement during the mound phase in Dictyostelium discoideum as revealed by ATP visualization and simulation

Cell migration plays an important role in multicellular organism development. The cellular slime mold Dictyostelium discoideum is a useful model organism for the study of cell migration during development. Although cellular ATP levels are known to determine cell fate during development, the underlying mechanism remains unclear. Here, we report that ATP-rich cells efficiently move to the central tip region of the mound against rotational movement during the mound phase. A simulation analysis based on an agent-based model reproduces the movement of ATP-rich cells observed in the experiments. These findings indicate that ATP-rich cells have the ability to move against the bulk flow of cells, suggesting a mechanism by which high ATP levels determine the cell fate of differentiation.

Age-associated differential microRNA levels in human follicular fluid reveal pathways potentially determining fertility and success of in vitro fertilization

Reproductive life span and fertility have been shown to depend on successful early folliculogenesis, which involves cell-to-cell communication and the concerted regulation of gene expression at both the oocyte and granulosa cell levels. Recently, micro RNAs (miRNAs) were identified as fine-tuners of gene expression. Here, we report that miRNAs can readily be detected within membrane-enclosed vesicles of human follicular fluid. MiRNA expression profiling of the follicular fluid of younger (<31 years) and older (>38 years) women revealed a set of four differentially expressed miRNAs. The predicted targets of these miRNAs are clearly enriched in genes involved in heparan-sulfate biosynthesis, extracellular matrix-receptor interaction, carbohydrate digestion and absorption, p53 signaling, and cytokine-cytokine-receptor interaction. Several of these pathways have been reported to be determinants of fertility, suggesting that this set of miRNAs and their respective targets should be evaluated in relation to reproductive aging and assisted reproduction.

Transfer of microRNAs by embryonic stem cell microvesicles

Microvesicles are plasma membrane-derived vesicles released into the extracellular environment by a variety of cell types. Originally characterized from platelets, microvesicles are a normal constituent of human plasma, where they play an important role in maintaining hematostasis. Microvesicles have been shown to transfer proteins and RNA from cell to cell and they are also believed to play a role in intercellular communication. We characterized the RNA and protein content of embryonic stem cell microvesicles and show that they can be engineered to carry exogenously expressed mRNA and protein such as green fluorescent protein (GFP). We demonstrate that these engineered microvesicles dock and fuse with other embryonic stem cells, transferring their GFP. Additionally, we show that embryonic stem cells microvesicles contain abundant microRNA and that they can transfer a subset of microRNAs to mouse embryonic fibroblasts in vitro. Since microRNAs are short (21–24 nt), naturally occurring RNAs that regulate protein translation, our findings open up the intriguing possibility that stem cells can alter the expression of genes in neighboring cells by transferring microRNAs contained in microvesicles. Embryonic stem cell microvesicles may be useful therapeutic tools for transferring mRNA, microRNAs, protein, and siRNA to cells and may be important mediators of signaling within stem cell niches.

Analysis of the extracellular matrix and secreted vesicle proteomes by mass spectrometry

The extracellular matrix (ECM) and secreted vesicles are unique structures outside of cells that carry out dynamic biological functions. ECM is created by most cell types and is responsible for the three-dimensional structure of the tissue or organ in which they are originated. Many cells also produce or secrete specialized vesicles into the ECM, which are thought to influence the extracellular environment. ECM is not s a physical structure to connect cells in a tissue or organ. The proteins in ECM and secreted vesicles are critical to cell function, differentiation, motility, and cell-to-cell interaction. Although a number of major structural proteins of ECM and secreted vesicles have long been known, an appreciation of the role of less-abundant non-collagenous proteins has just begun to emerge. This chapter outlines a series of methods used to isolate and enrich ECM constituents and secreted vesicles from bone-forming osteoblast cells, enabling comprehensive profiles of their proteomes to be obtained by mass spectrometry. These methods can be easily adapted to study ECM and secreted vesicles in other cell types, primary cell cultures derived from animal models, or tissue specimens.