Quantum dots are powerful multipurpose vital labeling agents in zebrafish embryos.

Recently, inorganic fluorescent contrast agents composed of semiconductor materials have been introduced to biological imaging approaches. These so-called quantum dots provide unique and promising properties unreached by organic fluorophores, but their use as contrast agents within live organisms has been limited, probably due in part to concerns about their in vivo tolerance. Using transparent zebrafish embryos, we challenged quantum dots with a series of intravital imaging problems. We show that quantum dots provide a high fluorescent yield within targeted tissues, possess immense photostability, can be targeted to specific subcellular compartments, remain within targeted cells as lineage tracers, are easily separable from conventional organic fluorescent dyes, and are fixable, allowing them to be used in combination with immunohistochemistry after live recordings. Thus, quantum dots combine the specific advantages of different organic fluorescent contrast agents and promise to become the first fluorophore feasible for long-lasting intravital time-lapse studies. Finally, we show by co-labeling blood vessels of the vasculature and major axon tracts of the nervous system that, for establishing these networks, the same guidance cues might be used in some body parts, whereas in others, both networks appear to develop independently from one another. Thus, the bright fluorescence of quantum dots will help to unravel many open questions in the fields of embryology, cell biology, as well as phenotyping and disease diagnosis.

Asymmetric localization of LGN but not AGS3, two homologs of Drosophila pins, in dividing human neural progenitor cells.

Human neural progenitor cells (hNPCs) can be recovered from postmortem human brains and used to study the molecular basis of neurogenesis. Human NPCs are being used to investigate the molecular basis of cell fate determination during stem cell divisions, based on comparison with the Drosophila model system. Drosophila neuroblasts and sensory organ precursors undergo well-defined asymmetric cell divisions (ACD), under the control of a genetically defined set of apical and basal determinants that are localized tightly and dynamically during division. We show by indirect immunofluorescence, confocal microscopy, and time-lapse video-microscopy that LGN and AGS3, two human homologs of the Drosophila ACD determinant Pins, have distinct patterns of localization in hNPCs. When cells are grown under conditions favoring proliferation, LGN is distributed asymmetrically in a cell cycle-dependent manner; it localizes to one side of the dividing cell and segregates into one of the daughter cells. When the cells are grown under conditions favoring differentiation, LGN accumulates in double foci similar to those containing the mitotic apparatus protein NuMA, and in a pattern shown previously for LGN and NuMA in differentiated cells. AGS3, a slightly more distant Pins homolog than LGN, does not show asymmetric localization in these cells. The progenitor cell marker nestin also localizes asymmetrically in colcemid-treated hNPCs and colocalizes with LGN. The results suggest that hNPCs undergo ACD and that similar molecular pathways may underlie these divisions in Drosophila and human cells.

Quantum dot-labelled polymer beads by suspension polymerisation.

CdSe quantum dots with polymerisable ligands have been incorporated into polystyrene beads, via a suspension polymerisation reaction, as a first step towards the optical encoding of solid supports for application in solid phase organic chemistry.