Chemotaxis…taxis in molecular rivers

Remember the scene from Lion King…..

Scar: Now you wait here. Your father has a marvelous surprise for you. Simba: Oooh. What is it? Scar: If I told you, it wouldn’t be a surprise, now would it? Simba: If you tell me, I’ll still act surprised. Scar: Ho ho ho. You are such a naughty boy. Simba: Come on, Uncle Scar. Scar: No-no-no-no-no-no-no. This is just for you and your daddy. You know, a sort of… father-son… thing.

Then follows a stampede of gazillions of creatures rushing through the gorge…a sad ending, Mufasa the king of the Pride Lands the father of Simba is no more but Simba lives not only to tell his story but to write even more stories….

The circle of life kind of begins like that but at a miniature scale…

Creature participating in the stampede are no other than simba’s little brothers and sisters competing with each other to survive and thrive and leave their mark on this grand canvas of life. The only difference is that those participating in stampede are not beasty creatures with strong legs and muscles but unicellular organisms with wagging tails and they swim in molecular rivers instead of sprinting through the gorge.

The sprint itself is a fascinating story, we have talked about molecular rivers a lot now lets talk about taxis that run in these rivers. The process behind the epic sprint is called Chemotaxis.

Chemotaxis (chemo + taxis) is the movement of an organism in response to a chemical stimulus. Many life forms are known to direct their movements according to certain chemicals in their environment in order to find food, get away from the nasty chemicals or find their mate. This is one of the simplest mechanisms that enables many creatures to perform fundamental actions to sustain life at molecular level. The actions being…

1) Find prey

2) Avoid predator

3) Find mate

Chemotaxis is achieved in bacteria by integrating sensory signals received from receptors on their bodies and by modulating the direction of flagellar rotation in response, flagella is microscopic tail that serve the purpose of a rudder and propeller to steer and propel these tiny boats towards food or away from harms way.

E. coli, the bacteria that lives in our gut feeds itself using a similar mechanism, It has four transmembrane chemoreceptors, known as methyl-accepting chemotaxis proteins (MCPs). These MCP’s are sensor proteins that allows bacteria to detect concentrations of molecules in the extracellular matrix. Depending on what binds to these receptors bacteria will continue to either taxi towards it if it is food or taxi away from it if it is poisson.

We are not the only ones with five sense, Escherichia coli has same number of chemotaxis sensors. Trg,for ribose and galactose; Tar, for amino acid aspartate Tsr for amino acid serine; Tap, for taxi towards peptides and Aer for aerotaxis or taxi towards oxygen.

Our immune system works in a similar way the white blood cells very much behave like these bacteria, independent creatures swimming in the bloodstream towards the concentration gradient to find and eat their food.

Here is nice illustration of a neutrophil navigating its way trying to catch bacteria and bacteria is running away from it . BTW neutrophils are type of white blood cells, 50 to 80 percent of all the white bloods cells in our body are neutrophils.

Here is another one, showing how neutrophils respond to chemicals …

These little creatures don’t have sharp claws and teeth, they use a mechanism called phagocytosis to surround and eat their food, once again all this is mediated by the receptors on the membranes. It is the receptors that not only sense the food, but hold it in place while the organisms can morph itself to surround the prey and digest it.

Here is an example of phagocytosis in progress, an amoeba eating a paramecium, please advance the video by 30 seconds to watch the real action.

Now coming back to the stampede question, the greatest swim of our lives, the swim everyone can claim to have won by outcompeting their little unborn brothers and sisters is also empowered by chemotaxis.

The spermatozoa, little creatures whose only job is to carry the torch and light the cauldron of life, behave the same way as the bacterial creatures swimming in search of food. Spermatozoa swim towards the chemoattractant and orient their swimming direction up the concentration gradient towards the oocyte. The chemoattractant that forms the gradient is progesterone. Progesterone is secreted by cells that surround the oocyte and it leaves the chemical trail for spermatozoa to complete and complete their journey to deliver the biological payload for the egg to start life. So if Simba’s of the world survive, thrive and continue to sing this sonnet of epic proportions that we call life, it is all grounded in this simple script of chemotaxis that we inherited from our ancestral life forms.

There is another interesting aspect linked to the chemotaxis. Migration of embryonic stem cells to various body parts is also believed to be mediated by chemotaxis. Postmortem examination of patients who died from lymphocytic leukemia and received bone marrow transplants indicates that bone marrow cells migrate to the brain to form new neurons. How they ended up with this remarkable discovery is when they started questioning the presence of male neurons in brains of females.

Now when we look at individual actions of the cells floating around within our bodies , they all seem to have an independent existence, much like ants in a colony, most of the decisions they make are by following very simple rules, rules that were tested and tried for millions of years in nature’s lab, rules that were carefully calibrated to deal with dynamic nature of evolving ecosystem, rules that create the symbiotic harmony among all participating beneficiaries of the ecosystem.

Moreover the ecosystem that these gazillions of creatures are participating in seems to be governed by some special kind of creatures, creatures who have decided to migrate to this special place in our head and created the seat of democracy. Looks like these special creatures have dissolved the thinking ability of everything else around them and now everyone is singing to the same tune calling themselves as one, part of one big system that we often identify with ‘I’.

So where does it leave ‘I’, ‘I’ as in ‘in-charge’, in-charge of this magnificent, awe-inspiring colony of dedicated, committed, unwavering, faithful, skillful, diverse creatures with equally fascinating abilities to be part of this moving and evolving ecosystem.

Or if you are with a philosophical bend we are kind of moving temples with god neurons at the altar and rest of the cells as devotees following the sacred mantras, participating in elaborate rituals, dancing to the mystical tunes, while the gods pump the good stuff in synaptic cleft leaving all spellbound.

Ref: http://www.pnas.org/cgi/content/long/100/3/1364. Photo Courtsey : https://www.flickr.com/photos/donotlick/

Originally published at scriptgrandeur.wordpress.com on April 6, 2015.