The ECM: A Dynamic System for Moving Our Cells

In part I of this series, we mentioned that the extracellular matrix (ECM) makes our tissues stiff or squishy, solid or see-through. Here, we reveal how the ECM helps body cells move around, a process vital for wounds to heal and a fetus to grow.

Sealing and Healing Wounds

MMPs are essential for closing wounds. Credit: Stock image.

When we get injured, the first thing our body does is to form a blood clot to stop the bleeding. Skin cells then start migrating into the wound to close the cut. The ECM is essential for this step, creating a physical support structure—like a road or train track—over which skin cells travel to seal the injured spot.

The ECM is made up of a host of proteins produced before and after injury. Some other proteins called matrix metalloproteinases (MMPs) also crowd into wounds. Because humans have so many different MMPs—a full 24 of them!—it’s been difficult for scientists to figure out what roles, if any, the proteins play in healing scrapes and cuts. Continue reading

The Extracellular Matrix, a Multitasking Marvel

In part II of this series, we reveal how the ECM helps body cells move around, a process vital for wounds to heal and a fetus to grow. Here we introduce the extracellular matrix (ECM) and discuss how it makes our tissues stiff or squishy, solid or see-through.

When we think about how our bodies are made and what they do, we usually focus on organs, tissues and cells. These structures have well-known roles. But around, within and between them is a less understood material that also plays an essential part in making us what we are.

This gelatinous filler material is known as the extracellular matrix (ECM). Once thought to be the biological equivalent of bubble wrap, we now know that the ECM is a dynamic, physiologically active component of all our tissues. It guides cell shape, orientation and function.

The ECM is found in all of our body parts. In some tissues, it’s a thin layer separating cells, like mortar between bricks. In other tissues, it’s the major constituent.

The ECM is most prevalent in connective tissue, the material that forms our skeletons, cushions our internal organs and winds between blood vessels and around nerves. In connective tissue, the ECM is more abundant than the cells suspended within it.

The extracellular matrix meets the needs of each body part. In teeth and bones, it’s rock-hard. In corneas, it’s a transparent gel that acts like a camera lens. In tendons, it forms strong fibers that bind muscle to bone. Credit: Stock image.

What makes the ECM truly unique is its variability: Its texture, composition and functions vary by body part. That’s because the ECM’s deceptively simple recipe of water, fibrous proteins and carbohydrates has virtually endless variations.

In general, the fibrous proteins give the ECM its texture and help cells adhere properly. Carbohydrates in the ECM absorb water and swell to form a gel that acts as an excellent shock absorber. Continue reading

The Science of Size: Rebecca Heald Explores Size Control in Amphibians

Rebecca Heald
Credit: Mark Hanson.
Rebecca Heald
Grew up in: Greenville, Pennsylvania
Studied at: Hamilton College, Rice University, Harvard Medical School
Job site: University of California, Berkeley
Favorite hobby: Cycling

A 50-pound frog isn’t some freak of nature or a creepy Halloween prank. It’s a thought experiment conceived by Rebecca Heald, a cell biologist at the University of California, Berkeley Exit icon, who is studying the factors that control size in animals.

Heald’s “50-pound frog project” speaks to the power of evolution and to scientists’ ability to modify the physical characteristics of an organism by altering its genome. The project also incorporates many of Heald’s fascinating discoveries studying amphibian eggs and embryos.

In amphibians, unlike in mammals, there are striking correlations among the size of the animals’ genomes (an organism’s complete set of genes) and several aspects of the animals’ size. For example, amphibians with large genomes tend to be bigger than those with smaller genomes. Larger genomes also correspond to larger cells and larger organelles (specialized cellular structures such as the nucleus). Heald has also demonstrated that these seemingly fixed parameters can be tweaked in the lab. Continue reading

Pigment Cells: Not Just Pretty Colors

If you’ve ever visited an aquarium or snorkeled along a coral reef, you’ve witnessed the dazzling colors and patterns on tropical fish. The iridescent stripes and dots come from pigment cells, which also tint skin, hair and eyes in all kinds of animals, including humans. Typically, bright colors help attract mates, while dull ones provide camouflage. In humans, pigment helps protect skin from DNA-damaging UV light.

Researchers study cellular hues not only to decipher how they color our world, but also to understand skin cancers that originate from pigment cells. Some of these researchers work their way back, developmentally speaking, to focus on the type of cell, known as a neural crest cell, that is the precursor of pigment cells.

Present at the earliest stages of development, neural crest cells migrate throughout an embryo and transform into many different types of cells and tissues, including nerve cells, cartilage, bone and skin. The images here, from research on neural crest cells in fish and salamanders, showcase the beauty and versatility of pigment cells in nature’s palette.

Xanthophores
Pigment cells called xanthophores, shown here in the skin of the popular laboratory animal zebrafish, glow brightly under light. Credit: David Parichy, University of Washington.
Melanocytes
Dark pigment cells, called melanocytes, like these in pearl danio, a tropical minnow and relative of zebrafish, assemble in skin patterns that allow the animals to blend into their surroundings or attract mates. Credit: David Parichy, University of Washington.
Fin of pearl danio
Pigment cells can form all sorts of patterns, like these stripes on the fin of pearl danio. Credit: David Parichy, University of Washington.
Salamander skin
Pigment cells arise from neural crest cells. Here, pigment cells can be seen migrating in the skin of a salamander where they will form distinct color patterns. Credit: David Parichy, University of Washington.

 

A Labor Day-Themed Collection: Hard-Working Cell Structures

Hard labor might be the very thing we try to avoid on Labor Day. But our cells and their components don’t have the luxury of taking a day off. Their non-stop work is what keeps us going and healthy.

Scientists often compare cells with small factories. Just like a factory, a cell contains specialized compartments and machines—including organelles and other structures—that each play their own roles in getting the job done. In the vignettes below, we give a shout out to some of these tireless cellular workers.

Energy Generators
Credit: Thomas Deerinck, National Center for Microscopy and Imaging Research
Mitochondria are the cell’s power plants. They convert energy from food into a molecule called ATP that fuels virtually every process in the cell. As shown here, mitochondria (brown) often have distinct, oblong shapes. Like most other organelles, mitochondria are encased in an outer membrane. But they also have an inner membrane that folds many times, increasing the area available for energy production. In addition, mitochondria store calcium ions, help make hemoglobin—the vital iron-containing protein that allows red blood cells to carry oxygen—and even take part in producing some hormones. Defects in mitochondria can lead to a host of rare but often incurable diseases that range from mild to devastating. Researchers are studying mitochondria to better understand their manifold jobs in the cell and to find treatments for mitochondrial diseases.

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