Sticking Together

You remember Kindergarten – that place where you left your home and entered an altered dimension in which the teacher ordered your world? At each time of the day there were different activities which required different levels of autonomy. Much of the day you spent in some group of students in which you all were working together on the same activity, but each student did their own work. Sometimes you were under more strict control – you know: hold hands with your partner and stay in a line. When recess came, you were much freer to roam and play as long as you stayed inside the boundaries. Finally, at the end of the day your teacher (much to his/her relief) let you loose to go home.

This common life experience forms a weak analogy for how the cells of your body cooperate to keep you functioning. Unlike a Kindergartner, individual cells do not change how much they stick together, but different types of cells have varying degrees of autonomy. Most of your cells stick together in what is known as a tissue – all the cells doing the same task, but each cell does its own work. These cells form adhesions between each other, but there are gaps in between the cells which allow interstitial fluids to pass in between them. These fluids carry nutrients, hormones, antibodies and many other proteins which tend to the needs of the cells.

Different tissues will cooperate to form different organs in the body. So, cardiac muscle, blood vessels, and nerves will all adhere together to form a heart. At its outer surfaces, however, a heart will not adhere to other organs outside of itself – the heart is separate from the nearby lungs. It is good to hold things in place, though, so a special tissue known as connective tissue can do this job, but the organs remain separate. For instance, the length of your digestive tract is held in place in the abdomen so that it doesn’t get tied up in knots (usually).

A few examples of the approximately 200 different types of cells found in the human body

Other cells need to stick together more closely. In the lining of the intestine, the cells making up the boundary between your body and the lumen of your gut (where all your food moves through) form what are known as “tight junctions”. These cells have adhesions which completely block the movement of any fluids from your food into the rest of your body. This forces everything which is absorbed from your food and drink to enter the blood stream and get carried to your liver where toxins can (hopefully) be destroyed.

Still other cells in the body have a great deal of autonomy. Your red blood cells move freely through your arteries, capillaries and veins, and thankfully, don’t stick together. Doing so can be both a help or a harm. When you get a cut, red blood cells get stuck in the network of fibers formed by blood proteins to form a clot to stop the bleeding – a scab. Blood clots that form within the blood vessels, however, can cause problems and even be fatal. White blood cells have even more autonomy as they are free to leave the blood stream and move in between all the cells of the body in search of foreign substances to destroy.

There are even cells produced by your body which are intended to have complete autonomy, leaving the body all together. Here of course, I am referring to the reproductive cells. In humans, this move to complete autonomy is more gradual than we see in other organisms. The growing embryo/fetus resides in a space that can technically be considered “outside” the body, but continues to be nurtured by the parent of those cells until the time of birth.

What is interesting is that, after fertilization, the cells which begin to be produced through cell division all stick together with the same degree of adhesion. As development proceeds, the cells begin to differentiate, and begin to alter the amount of adhesion they make with neighboring cells. This adhesion occurs because of a class of molecules embedded in the cell membrane – complex protein-carbohydrate molecules referred to as “receptors” – which extend from the cell’s cytoskeleton, through the membrane and extend into the intercellular space to connect with the receptors of neighboring cells.

Different types of membrane bound receptors used for cell adhesion [1]

There is a great deal of specificity in these receptors. There are hundreds of these glycoproteins coded for in the genome – all of which is found in every single type of cell – but each cell type will only make use of a certain few. The specificity for adhesion is accomplished not only by the type of receptor used, but the combinations and amount of receptors produced as well. In addition to helping the cells stick together, these receptors also play a role in cell-cell communication which influences cell growth, cell morphology, cell survival and gene expression.

Like the Kindergarten, there is something among cells that is ordering the “classroom” – controlling which cells stick together and how strongly do they adhere. The “teacher” in this case is what is referred to as a gene regulatory network (GRN). In addition to the recipes for each of these receptors being coded in your DNA, there are another series of proteins coded for in the genome which, when expressed, serve to initiate the production and placement of the specific receptors for specific types of cells. Just as there are proteins which signal the production of these receptor molecules, there are others needed to inhibit the production.

When GRNs are mapped out for any particular biochemical pathway, they take on the appearance of complex computer programming diagrams. Such organizational systems demand a high level of foresight. For instance, the gene for a receptor would be of no use (and therefore not exist in the genome) without the proteins needed to start and end its production. These promoter and inhibitor proteins, however, would not exist without the pre-existence of the gene for the receptor. Since the construction of receptors involves more than just the transcription of a single protein, multiple interdependent genes are involved in the process.

Mapping of the gene regulatory network for the adhesion associated with cancer cells [2]

The deeper question in all this is how did this level of organization come to exist. Even the simplest multi-celled organisms require these complex systems to obtain cell adherence. The foresight and planning needed for this resists any type of evolutionary explanation. Random mutations and natural selection can only operate to modify existing genes and respond to extant conditions, and are not able to produce genes which anticipate future needs. Furthermore, the presence of information, and even more so, the presence of complex information processing systems cannot be explained by the outworking of natural laws. To instantiate such high levels of organization, I think it is more reasonable to infer that a designing intelligence was involved than random molecular interactions. Our common experience tells us that information comes from intelligent sources. Further, the use and processing of information (like the ordering the activity of Kindergartners) is also indicative of intelligent agency. I would further suggest that the effort to map GRNs presumes upon this. While the designer does not need to be “in the room” to make all this function, a designer was certainly required to put it in place.

[1] Hynes RO. Cell adhesion: old and new questions. Trends Cell Biol. 1999 Dec;9(12):M33-7. PMID: 10611678.

[2] Selvaggio, G.; Chaouiya, C.; Janody, F. In Silico Logical Modelling to Uncover Cooperative Interactions in Cancer. Int. J. Mol. Sci. 2021, 22, 4897. ijms22094897

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