Febrary 26, 2014

Not all stem cells are created equally. Some are totipotent, meaning they can divide and differentiate into any cell type, while some are unipotent, meaning they can differentiate into one specific cell type. Understanding the potenty of various stem cells is an important step towards understanding how tissues are developed, remodeled, and maintained. Today’s beautiful images are from a study of stem cells in the mammary gland.

Mammary glands go through a lot of changes during both puberty and adulthood, and are made up of two main cell lineages—myoepithelial and luminal. The function of mammary stem cells was previously unclear—in one model, bipotent stem cells contribute to the development and maintenance of adult mammary glands, while in the other model, those stem cells are unipotent and separately control mammary gland lineages. A recent cell fate mapping study by Rios and colleagues featured the use of multicolor reporters and 3D imaging. Rios and colleagues found that mammary stem cells are indeed bipotent, and function in ductal remodeling and homeostasis in the adult mammary gland. In the image above, the sea of colorful cells seen in the mid-puberty mouse mammary gland (top) indicates the presence of multiple progenitors. The arrow and arrowhead in the inset image point to myoepithelial and luminal cells, respectively. As puberty progressed (bottom), discreet regions of similarly-colored cells indicate clonal expansion and a shift towards adulthood.

Rios, A., Fu, N., Lindeman, G., & Visvader, J. (2014). In situ identification of bipotent stem cells in the mammary gland Nature, 506 (7488), 322-327 DOI: 10.1038/nature12948
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

February 19, 2014

It will take cell biologists an eternity to understand how cells function in a dish. It will take developmental biologists even longer to understand how cells function within a developing organism. Today’s image is from a paper describing the use of liquid droplets as cell biological crash test dummies to determine cell-generated forces within living tissue.

The development of an organism and the generation of its organs depend on mechanical forces that can move cells and groups of cells. There are many techniques that have been helpful in understanding these forces, but these techniques have not been applicable for measuring forces in three dimensional living tissue (or, in the case of laser ablation, have only provided relative force measurements). Campàs and colleagues have just published a paper describing the clever use of oil microdroplets to measure force within living tissues and organs. These spherical microdroplets are a similar size as cells, are fluorescently labeled, and display cell surface adhesion receptors. After these microdroplets are injected into tissue, their deformation by surrounding cells exerting mechanical stress can be measured and quantified. The images above show a microdroplet (white arrow, top) embedded in an incisor tooth bud of a mouse embryo (E13.5). Higher magnification views of the microdroplet (bottom row) show the pixel-resolution contour of the droplet (middle). The higher curvature regions (arrows, right image) correlate with cell-cell junctions of adjacent cells. 

Campàs O, Mammoto T, Hasso S, Sperling RA, O'Connell D, Bischof AG, Maas R, Weitz DA, Mahadevan L, & Ingber DE (2014). Quantifying cell-generated mechanical forces within living embryonic tissues. Nature methods, 11 (2), 183-9 PMID: 24317254
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

February 13, 2014

Whenever I’m lucky enough to make it down the road to the amazing Georgia Aquarium, I find myself glued to the jellyfish tanks. I have always loved watching the graceful movements of the jellies, and as a cell biologist my fluorescently-tagged appreciation runs deep. Today’s image is from a paper describing the molecular pathways in jellyfish development.

The phylum Cnidaria are made of organisms that cycle through two completely different stages—polyps and jellyfish. The polyp-to-jellyfish transition is dramatic, as seen in the images above, and begins with a shift in water temperature. During strobilation, segment-like disks (white arrows) are formed progressively down the polyp. Each disk detaches from the strobila and becomes an ephyra, or young jellyfish, which then quickly matures to an adult jellyfish. A recent paper in Current Biology describes the molecular pathways important in the polyp-to-jellyfish transition in translucent moon jellies. Fuchs and colleagues found that two pathways are important—one relying on retinoic acid, and the other involving secreted proteins that are upregulated following shifts in temperature. One of these secreted proteins (CL390) serves as the precursor of the strobilation hormone in moon jellies.

Björn Fuchs, Wei Wang, Simon Graspeuntner, Yizhu Li, Santiago Insua, Eva-Maria Herbst, Philipp Dirksen, Anna-Marei Böhm, Georg Hemmrich, Felix Sommer, Tomislav Domazet-Lošo, Ulrich C. Klostermeier, Friederike Anton-Erxleben, Philip Rosenstiel, Thomas C (2014). Regulation of Polyp-to-Jellyfish Transition in Aurelia aurita Current Biology, 24 (3) DOI: 10.1016/j.cub.2013.12.003

Copyright ©2013 Elsevier Ltd. All rights reserved. 

February 5, 2014

The next time you try swatting away that little fruit fly from a neighboring lab while you enjoy your midday coffee break, take a beat and appreciate how stinkin’ purrrty those flies are. Today’s image features the developing egg of the fruit fly, and accompanies a paper describing the important role for prostaglandins in the (very photogenic) process.

Prostaglandins (PGs) are small lipids that act as signaling molecules in various physiological processes such as pain, inflammation, and platelet aggregation. On the cellular level, PGs regulate the organization of the actin cytoskeleton. A recent paper in Molecular Biology of the Cell from the Tootle lab sheds light on the role of PGs in development, and shows that PGs temporally regulate actin cytoskeleton organization during Drosophila oogenesis. Specifically, PGs function at stages 9 and 10 of oogenesis to inhibit, then promote, actin remodeling via the actin elongation factor Ena. Loss of PG signaling at stage 9 triggers early actin filament formation and bundling, while loss of PG signaling at stage 10 triggers a reduction of, or complete loss of, parallel actin filament bundling. As seen in the images above, actin filament organization (white) is abnormal in two different PG mutant follicles (middle, bottom), compared to a wild-type follicle (top).

Andrew J. Spracklen, Daniel J. Kelpsch, Xiang Chen, Cassandra N. Spracklen, & Tina L. Tootle (2014). Prostaglandins temporally regulate cytoplasmic actin bundle formation during Drosophila oogenesis Molecular Biology of the Cell, 25 (3) DOI: 10.1091/mbc.E13-07-0366