Saturday, June 30, 2012

From Tadpole to Frog

Most of us have wondered at tadpoles ... why do their tails disappear as their legs appear? ... and how does that happen?

Last night I watched a movie suggested by a friend ... "Death by Design," described below.  It focuses on programmed cell death discussing the system of communication among the 50-100 trillion cells in our body.  One major point is that cells don't "just die," they receive a signal to die and have to take an action to set their death in motion.  Well now, this opens up a whole can of worms about who/what/how is doing that signaling ... who or what wrote the program?

And, it isn't just death that is operating on a program.  One segment of the movie talks about the life of a tadpole and the death of the tail cells that happens just as the new growth of leg cells begins.  The tail cells and the leg cells are signaled to start their engines ... one toward death and one toward growth.

One can be totally flummoxed by the beauty, mystery and symmetry of this system. Some sort of intelligence knows that a tail for fast swimming would make the tiny, unprotected tadpole more likely to survive tadpolehood, but in order to survive as a breeding frog, legs would be better.  Talk about intelligent design! (This is not intended to support the telelogical, anti-evolutionary theory of Intelligent Design.  While it would be hard to say that a creative force in the Universe does not exist ... it may look nothing like what we puny humans have designated "God.")

Back to cell death.  One statement in the movie explored the time line of development, saying that it took 3 billion years to develop from a single cell organism to a multi-cell organism.  I get impatient waiting for my tea water to boil, so this idea that it took so long to basically go from 1 to 2 is a little incomprehensible.

Watching the video below helped put that into perspective.  "One" wasn't just one free-floating, ignorant little cell.  The ones that survived were smart enough to find food, survive the conditions of the world around them, form into cooperative (although unconnected) groups and reproduce their little selves.  They developed a "tool kit" that prepared them for the shift to greater complexity.

In case you aren't completely befuddled by the beautiful complexity of life, consider these examples from Wikipedia on "Phenotopsis" (programmed death of organisms):

Mayfly – Adult mayflies have no functional mouth and die from malnutrition.[2]
Praying mantis – The male praying mantis ejaculates only after being decapitated by the female.[9]
Tick Adactyllidium – The initial food source of Adactyllidium tick larvae is the body tissues of their mother resulting in her death.[6]
Squid – Some male squid die immediately after mating. This provides an abundant food source for those predators that would prey on the eggs. [10]
Marsupial mice – Males die 2 weeks after reproducing from an overabundance of their own [pheromones].[6]
Salmon – Die soon after spawning.[11]

Septic shock – Infection by pathogens often results in death by sepsis. Sepsis, however, is not a result of toxins activated by the pathogen, rather it is directed by the organism itself. Similar to phenoptosis of E. Coli, this is a means to separate dangerously infected individuals from healthy ones. [5]

This seems to be enough food for thought on this beautiful morning on the Central Coast of California ... I'm off to see multicelled organisms in action on the beach.

More Info:

Death By Design/The Life and Times of Life and Times  (available from Netflix Instant Queue)
Pierre Golstein (Actor), Polly Matzinger (Actor), Peter Friedman (II) (Director), Jean-François Brunet (Director) | Rated: NR | Format: DVD
Death by Design, a witty, fast-paced documentary by Peter Friedman (working with French researcher Jean-Francois Brunet), concerns an unlikely but fascinating subject: programmed cell death. Taking us deep into the mysteries of cellular biology, Friedman reveals the arcane reasons why some cells suddenly and automatically kill themselves, apparently triggered by signals from surrounding cells. Friedman employs some impressive, microscopic cinematography, but he knows most people are not inclined to look at the building blocks of life even for an hour. So he makes clever, allegorical use of other bits of film--clips of cars driving on the freeway, animation, Busby Berkley musical numbers, Harold Lloyd--to underscore the major points. Wonderfully entertaining and enlightening, Death by Design makes the invisible a thing of kinetic beauty.

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