By Wallace Marshall
Dr. Marshall refutes the commonly held idea that cells are just bags of watery enzymes. He runs through his “Top 10 List” of unexpected and amazing things that individual cells can do. These including growing to be huge, navigating mazes, and performing feats that seem to belong in science fiction.
Dr. Wallace Marshall is a Professor of Biochemistry and Biophysics at the University of California, San Francisco. He is also a Director of the Physiology Summer Course at the Marine Biological Laboratory in Woods Hole. Marshall’s lab is interested in how single cells count and measure to determine cell size, number and organization. They have developed the single celled giant ciliate Stentor coeruleus as a molecular and genomic model organism for these studies.
- Cells that get really big
- Cells that walk and can attack other cells
- Cells that go left
- Tunneling nanotubes
- Cells that can sense electricity
- Cells that can solve mazes
- Cells that can see
- Exploding cells
- Cells that eat your brain and control your mind
The Myth: Cells are small, simple, and stupid
- Cells are small and simple building blocks (similar to atomic theory)
- Cells are separate compartments of living matter (hence the name Cell)
Cells are not necessarily simple, they can be very complicated and make beautiful shapes. For example in the following picture there are free-living cells and cells from the bodies of animals. They are much more complicated than a bag of enzymes.
#10. Cells that get really big
Gromia sphaerica is a 1.5 inch diameter amoeba and leaves trails on ocean floor.
“Gromia in situ closeup” by Mikhail Matz – Mikhail Matz / Harbor Branch Oceanographic Institution. Licensed under Public Domain via Commons – Gromia in situ closeup
“Gromia-field wInset” by Mikhail Matz – Mikhail Matz / Harbor Branch Oceanographic Institution. Licensed under Public Domain via Commons – Gromia
Acetabularia looks like a flower and is a single-cell green alga and reaches 10 cm long. It is the largest single cell we know.
E. Haeckel illustration: Acetabularia acetabulum. Algae commonly known as Mermaid’s wine glass.
Multinucleate cells can be even bigger, for example Caulerpa. This one cell makes brunches and can be larger than a human being.
Some cells though can be extremely small, for example Eukaryote Ostreococcus tauri which is only one micron in diameter.
Ostreococcus tauri strain OTH95, photo courtesy of Hervé Moreau, Laboratoire Arago
Left Tomographic slice (2D section computationally extracted from the 3D tomogram) from an O. tauri cell. Labels: nucleus N, chloroplast C, Golgi body G, and mitochondrion M. Right 3-D segmentation of this cell. This remarkable free-living cell has evolved to carry out all the conserved functions in a tiny and compact volume. Source
#9. Cells that walk and can attack other cells
Stylonychia. If you did not know better you’d think they are a small insect, but in fact this is a cell.
Y el coco llegó, stylonychia
Vampire cells: Dileptus. They have a sharp needle that they can poke other cells and drink their cytoplasm.
“Dileptus species” by Deuterostome – Own work. Licensed under CC BY-SA 3.0 via Commons – Dileptus
Mega-mouth cells: Didinium. They can open gigantic mouth and swallow other cells.
“Didinium nasutum consuming a paramecium” by S. O. Mast – The Reactions of Didinium nasutum (Stein) with Special Reference to the Feeding Habits and the Function of Trichocysts, Biological Bulletin, 1909. Licensed under Public Domain via Commons – Didinium nasutum consuming a paramecium
#8. Cells that go left
White blood cells tend to move left. These cells know left from right, how does a watery bag of enzymes can know left from right?
Leftward bias of differentiated HL-60 (dHL-60) cell polarity. The bias of cell polarity was assessed by observing the locations of an individual cell’s centrosome.
Xu J et al. (2007), PNAS, 104:9296-9300
One structure in a cell that may be able to determine left from right is a centriole. Ability and decision making of cells when they move are probably more crazy then we could have imagined.
#7. Tunneling nanotubes
Fundamental part of cell theory is that cells are disconnected from each other, that’s what makes them cells. But in fact we know that cell often are connected with each other. In animals tunneling nanotubes allow cells to connect to each other and exchange chemicals.
In animals: Tunneling nanotubes
Scanning electron micrograph showing a thin membrane tube (referred to as tunneling nanotube, TNT) connecting two cultured PC12 cells. Bar, 10 mm.
This picture demonstrates a variety of tubulovesicular extensions in human neutrophils revealed by scanning electron microscopy. Flexible extensions with unattached tips (B,C,E), flexible (B-F) and strait (B,C,E) extensions connecting neutrophils are presented. Flexible extensions consist of tubular and/or vesicular interconnected fragments.
From: Cytonemes as Cell-Cell Channels in Human Blood Cells, Madame Curie Bioscience Database [Internet]. Austin (TX): Landes Bioscience; 2000.
In plants: plasmodesmata
Plasmodesmata between plant cells. The cytoplasm of one plant cell is continuous with the cytoplasm of its neighbors via plasmodesmata, channels through the cell walls.
Leukocyte Transcellular migration. In this case white blood cells (leucocytes) want to escape from a blood vessel and attack invading organisms in your tissue, to do that they have to get through the epithelial layer, but epithelial cells are very tight and the blood cells cannot squeeze past them, so instead they dive right through them. You can have a leucocytes crawl inside other cells and it is happening all the time right now in your bodies.
From the following article: The cell biology of cell-in-cell structures
Michael Overholtzer & Joan S. Brugge
Nature Reviews Molecular Cell Biology 9, 796-809 (October 2008)
Argosomes. Signaling proteins may set up gradients by moving in membrane fragments, dubbed argosomes.
by Suzanne Eaton and colleagues (Max Planck Institute, Dresden, Germany).
GFPgpi (green) spreads from the expressing region (right) attached to argosomes. Eaton/Elsevier
Kleptoplasty is a symbiotic phenomenon whereby plastids, (notably chloroplasts), from algae are sequestered by host organisms. Which means, the animals eat other cells and digest them, but then save organelles from that cell and put them inside of itself.
A, Adult E. chlorotica feeding on its algal prey, the coenocytic heterokont V. litorea. Bar = 5 mm. B, Confocal micrograph showing the red autofluorescent plastids densely packed within the digestive diverticula of E. chlorotica. Once established, these plastids remain photosynthetically active within the adult for several months. Bar = 50 μm.
Cell fragments that can move by themselves. No nucleus, no centrosome, no Golgi. Under certain conditions, a piece of a cell will decide to take off on itself. In the image below a piece of a cytoplasm decided to crawl away.
Platelets are fragments of a cell that freely move in the blood.
Large progenitor cells in the bone marrow called megakaryocytes (MKs) are the source of platelets. MKs release platelets through a series of fascinating cell biological events. During maturation, they become polyploid and accumulate massive amounts of protein and membrane. Then, in a cytoskeletal-driven process, they extend long branching processes, designated proplatelets, into sinusoidal blood vessels where they undergo fission to release platelets.
#5. Cells that can sense electricity
Now we are getting into realm of truly crazy.
Galvanotaxis. Electrotaxis (or galvanotaxis) is the directional movement of motile cells in response to an electric field. It has been suggested that by detecting and orienting themselves toward the electric fields, cells are able to direct their movement towards the damages or wounds to repair the defect. It also is suggested that such a movement may contribute to directional growth of cells and tissues during development and regeneration. This notion is based on 1) the existence of measurable electric fields that naturally occur during wound healing, development and regeneration; and 2) cells in cultures respond to applied electric fields by directional cell migration – electrotaxis / galvanotaxis.
Generation of endogenous electrical potentials and injury currents. (A) A non-keratinized epidermal epithelium composed of an apical squamous and basolateral cuboidal layer is illustrated with a transepithelial electrical potential of +50 mV. (B) A section of the cuboidal layer where single epithelial cells, connected by tight junctions, prevent free diffusion of ions or current flow between the apical to basolateral surfaces. Polarized ion transport across tight-junction-connected single cells gives rise to net movement of positive charge and generates an electrical potential difference. Here, the basolateral localization and activity of the electrogenic Na+-K+ ATPase is primarily driving the net charge movement across connected cells. (C) An injured epidermal epithelium gives rise to a low-resistance pathway, short-circuiting the epithelial battery and generating current flow near the site of injury. The arrow direction indicates the movement of positive charge. (D) A neuron with cell body and extending axon. (E) Cross-section of the axon depicting a resting membrane potential of –70 mV generated primarily by the electrogenic Na+-K+ ATPase. (F) Injury gives rise to a low-resistance pathway, and electrical current (movement of positive charge) is directed into the cell, indicated by the arrows.
Electric fields direct migration of zebrafish keratocytes. (A) Photograph of migrating keratocytes after application of an EF of 100 mV/mm. Cells align perpendicular to the EF lines and migrate toward the cathode (Huang et al., 2009). (B) A higher degree of polarization and directed migration occur with increasing field strength. Both single cells and cell sheets migrate toward the cathode with a sensitivity of 7 mV/mm. The cosine measures the extent to which the cell population migrates toward the cathode (–1) or the anode (+1). Values near zero indicate relatively random migration. (C) Plots of the paths of migration for different cells exposed to different field strengths. The starting points of migration have been normalized to the origin. Migration into all four quadrants is shown for cells migrating in the absence of an EF, indicating random migration. Directed migration to the left, 2nd and 3rd quadrants, increases with increasing field strength.
Extracellular Electrical Fields Direct Wound Healing and Regeneration
Mark A. Messerli, and David M. Graham
The Eugene Bell Center for Regenerative Biology and Tissue Engineering and The Cellular Dynamics Program, Marine Biological Laboratory, Woods Hole, Massachusetts 02543
Reference: Biol. Bull. 221: 79 –92. (August 2011)
© 2011 Marine Biological Laboratory
#4. Cells that can solve mazes
Physarum. We really do not know how much computation cells can perform. One classic example is cells tat can solve mazes finding a shortest path to the food.
How Brainless Slime Molds Redefine Intelligence [Video]
Single-celled amoebae can remember, make decisions and anticipate change, urging scientists to rethink intelligent behavior
Fungi Use Efficient Algorithms for the Exploration of Microfluidic Networks
Kristi L. Hanson et al.
Cells can also solve the ‘traveling salesman’ problem.
Physarum syncytium recapitulates Tokyo subway map
Slime mold attacks simulates Tokyo rail network, by Ed Yong, 2010
Cells show simple learning (habituation). In the example below a cell stretches to eat which makes it vulnerable. Wen in danger it rolls into a little ball. How does it know when it is dangerous? The same way we do – by experience. Which raises a question: How much thinking can cells actually do?
#3. Cells that can see
Cells move towards IR light source
Cells align perpendicular to cells on the other side of a coverslip
Guenter Albrecht-Buehler, Ph.D.: Fellow, Institute for Advanced Studies, Berlin
Robert Laughlin Rea Professor of Cell Biology: Northwestern University Medical School, Chicago
#2. Exploding cells
There is nothing more extreme than to explode. By exploding, the cell breaches plant defences.
Putting the ‘blast’ in ‘rice blast fungus’ – Appressoria in Magnaporthe grisea
Scanning Electron Microscopy Images of Guy11 and the cut2 Mutant at 10 and 24 hpi on Hydrophobic Plastic.
Bars = 10 μm.
Turgor pressure 10 Mpa, about the same as bullet impact. In biology, turgor pressure or turgidity is the pressure of the cell contents against the cell wall, in plant cells, determined by the water content of the vacuole, resulting from osmotic pressure.
Cross-section of appressorium of wild Magnaporthe grisea.
Life cycle of the rice blast fungus Magnaporthe oryzae. The rice blast fungus starts its infection cycle when a three-celled conidium lands on the rice leaf surface.The spore attaches to the hydrophobic cuticle and germinates, producing a narrow germ tube, which subsequently flattens and hooks at its tip before differentiating into an appressorium. The single-celled appressorium matures and the three-celled conidium collapses and dies in a programmed process that requires autophagy. The appressorium becomes melanized and develops substantial turgor. This translates into physical force and a narrow penetration peg forms at the base, puncturing the cuticle and allowing entry into the rice epidermis. Plant tissue invasion occurs by means of bulbous, invasive hyphae that invaginate the rice plasma membrane and invade epidermal cells. Cell-to-cell movement can initially occur by plasmodesmata. Disease lesions occur between 72 and 96 hours after infection and sporulation occurs under humid conditions; aerial conidiophores with sympodially arrayed spores are carried to new host plants by dewdrop splash.
Under Pressure: Investigating the Biology of Plant Infection by Magnaporthe oryza
Nicholas J. Talbot – University of Exeter
Richard A. Wilson – University of Nebraska – Lincoln
More general relevance of hydrostatic pressure: motility by ‘Belbbing’.
#1. Cells that eat your brain and control your mind
It turns out, it is not as bad for you.