July 24, 2014

How many times can you say the word “gonad” in a sentence without giggling? If the answer is none, then I congratulate you on turning thirteen. If the answer is many, then you must be a biologist. Biologists appreciate the value of a good gonad, and so should you. The gonad of the worm C. elegans serves as an important model in which to study tissue organization and development, as you’ll see in the paper that accompanies today’s image.

At the end of cell division, cytokinesis typically results in two separate daughter cells. Some cytokinesis, though, is incomplete and leads to two daughter cells sharing cytoplasm. This shared cytoplasm, or syncytium, can be found in the germ cells of many species from worms to humans. The germline of the worm C. elegans is a polarized tube in which germ cells are arranged around the shared cytoplasmic core and move along a conveyer belt of oocyte production. Amini and colleagues recently reported on the formation of the syncytial C. elegans germline throughout development, and the role of the short Anillin family scaffold protein ANI-2. ANI-2 is localized to the intercellular bridges that connect the germ cells to the shared cytoplasm, and loss of ANI-2 results in destabilization of intercellular bridges and sterility. The defects seen in worms lacking ANI-2 are likely due to a loss of the stability and elasticity of the intercellular bridges that is required to compensate for the stress of cytoplasmic streaming during oogenesis. Images above show the germlines of wild-type and ani-2(-) worms at different larval stages (membranes in green; nuclei in red). Worms lacking ANI-2 have abnormal multinucleated germ cells (arrowheads).

Amini, R., Goupil, E., Labella, S., Zetka, M., Maddox, A., Labbe, J., & Chartier, N. (2014). C. elegans Anillin proteins regulate intercellular bridge stability and germline syncytial organization originally published in the Journal of Cell Biology, 206 (1), 129-143 DOI: 10.1083/jcb.201310117

June 30, 2014

Which came first, the primordial germ cell or the gamete? Unlike the old chicken or egg philosophical dilemma, we know for certain that the primordial germ cell came first. And, thanks to a recent paper about primordial germ cells in sea urchins, we now know that they can migrate across the urchin embryo.

During development, germ cells produce gametes (eggs or sperm). In many organisms, including mammals, primordial germ cells (PGCs) are born far from the eventual location of gametes and must migrate across the embryo while dividing. In sea urchins, small cells called micromeres are PGCs and precisely segregate along the left-right axis of the embryo. A recent paper by Campanale and colleagues describes the use of live-cell imaging of small micromeres in urchin embryos to test whether the precise segregation of these eight micromeres is due to passive translocation or active migration. Images show that the micromeres are, in fact, motile cells with features such as cortical blebs and filopodia that direct migration across the sea urchin embryo, towards the coelomic pouches. In the images above, sea urchin embryos express micromere (red) and apical membrane (green) markers before (left) and during (middle, right) gastrulation.

Campanale, J., Gökirmak, T., Espinoza, J., Oulhen, N., Wessel, G., & Hamdoun, A. (2014). Migration of sea urchin primordial germ cells Developmental Dynamics, 243 (7), 917-927 DOI: 10.1002/dvdy.24133

June 21, 2013

Good things come in small packages.  Maybe I’m referring to the burst of antioxidants jammed into tiny blueberries.  Maybe I’m referring to my tiny three year-old who yells, “Come oooon, THAT was funny!” when I don’t laugh loudly enough at her jokes.  Or maybe I’m referring to C. elegans.  These worms are tiny, but pack a serious punch of significant biology that helps us learn about important cellular processes.  Today’s image is from a paper that serves as an excellent example of this.

During cell invasion, a cell is able to breach and cross over the basement membrane that underlies a sheet of epithelial cells.  Cell invasion occurs throughout development and in the spread of cancer, yet biologists studying cell invasion have been challenged by the difficulty of visualizing the event.  A recent paper describes the development of live-cell imaging methods for studying cell invasion, using the worm’s anchor cell.  The anchor cell in the developing worm’s uterus breaches the basement membrane in order to link uterine and vulval tissues, and its transmigration is precisely timed.  Hagedorn and colleagues followed the interactions between the invading anchor cell and the basement membrane, and found very dynamic actin-based invadopodia that first breach the basement membrane.  These protrusions then stabilize to expand the breach and cross into the vulval tissue.  Anchor cell invasion depends on the netrin receptor UNC-40 (DCC) at the interface between the anchor cell and basement membrane.  In the time-lapse images above, the invading protrusion (cyan in top, grayscale in bottom) can be seen breaching the basement membrane (purple) and invading the vulval tissue underneath.

Hagedorn, E., Ziel, J., Morrissey, M., Linden, L., Wang, Z., Chi, Q., Johnson, S., & Sherwood, D. (2013). The netrin receptor DCC focuses invadopodia-driven basement membrane transmigration in vivo originally published in the Journal of Cell Biology, 201 (6), 903-913 DOI: 10.1083/jcb.201301091

April 26, 2013

It’s Worm Week here at HighMag Blog.  Worms are amazing little creatures, and the species C. elegans is an invaluable model system for studying cell and developmental biology.  Their genome is sequenced, their development is precise and well-documented, and their bodies and embryos are translucent (making them photogenic under a microscope).  Today’s image is from the same lab that brought Tuesday’s image…worm gonads rock!

Blurb and image from Christian R. Eckmann:
The image is an immuno-stained part of an extruded C. elegans hermaphrodite gonad; germ cell nuclei (magenta) and the apical membrane (green). The germ stem cells reside at the closed end of this tube like tissue. In wild type, the germ stem cells exit the mitotic zone, entering meiosis further away from the closed tip and start differentiating into sperm or oocytes. 

The image posted earlier this week is from the Gracida and Eckmann paper that identifies a nuclear receptor that protects germ stem cell integrity, and in turn fertility, after dietary perturbations.

Gracida, X. & Eckmann, C. (2013). Fertility and Germline Stem Cell Maintenance under Different Diets Requires nhr-114/HNF4 in C. elegans Current Biology, 23 (7), 607-613 DOI: 10.1016/j.cub.2013.02.034 

April 23, 2013

I’m thankful that my body knows how to handle days when I feed it wonderful things, like a banana and a giant bowl of strawberries, then follow it up with a few gut-busting mini-doughnuts.  Although worms and other organisms don’t have access to doughnuts like I do, their bodies still have protections in place to handle changes in their diet.  Today’s image is from a paper describing how the germline is protected from a changing diet.

Organisms consume a variety of food options, yet their bodies know how to regulate these changes to maintain homeostasis, all the way down to the cellular level.  A recent paper shows how an organism’s germline stem cells (GSCs), the source of eggs and/or sperm, are protected from food intake.  Gracida and Eckmann found that the nuclear receptor NHR-114 protects GSCs from dietary perturbations in worms, possibly through a detoxifying response to certain food intake.  Without NHR-114, worms on certain bacterial diets become sterile due to germ cell division defects during development.  The dietary sensitivity is based on intake of the amino acid tryptophan.  In the images above, gonads of worms fed a certain bacterial diet are stained to see individual germ cells (cell cortex staining in green in merged; DNA is purple).  Compared to wild-type worms (left), worms depleted of NHR-114 (right) have germ cell defects, notably cells with multiple nuclei (arrowhead).

Gracida, X., & Eckmann, C. (2013). Fertility and Germline Stem Cell Maintenance under Different Diets Requires nhr-114/HNF4 in C. elegans Current Biology, 23 (7), 607-613 DOI: 10.1016/j.cub.2013.02.034 
Copyright ©2013 Elsevier Ltd. All rights reserved. 

April 7, 2011

What do you have in common with a worm? A lot, and you should be thankful! The worm C. elegans is used as a model system that allows researchers to learn an amazing amount about the genetic pathways and development in many systems, including our own. Thankfully for HighMag, the worms are quite photogenic too.

Our germ line is the line of cells that are responsible for passing on our genetic material to the next generation. The germline is composed of gametes (eggs and sperm), as well as the cells that divide to give rise to gametes. The cytoplasm of germ cells contain special aggregates of proteins and RNA called germ granules, yet their formation and function are not completely understood. A recent paper was published describing work on the germ granules, called P-granules, in the nematode C. elegans. Updike and colleagues probe further into the comparison of P-granules to nuclear pores and provide new information on the roles of different P-granule proteins. Interestingly, P-granules establish a size-exclusion barrier and are held together by hydrophobic interactions, similar to nuclear pores. Images above show the germ lines of a wild-type worm (left) and a worm with decreased levels of the P-granule protein GLH-1 (right). Without normal levels of GLH-1, the P-granules (green) were not able to localize to the surface of the nuclei (blue).

Updike, D., Hachey, S., Kreher, J., & Strome, S. (2011). P granules extend the nuclear pore complex environment in the C. elegans germ line originally published in The Journal of Cell Biology, 192 (6), 939-948 DOI: 10.1083/jcb.201010104