Beyond Lineage-Specific Biologyrecent study has investigated the different cell types in the retina of mice. The research focused on the number of cells present in the retina. That may not sound very interesting, but the results were indeed eye-opening.
The researchers looked at 12 different types of cells in the retina, across 30 different strains of mice. Naturally they expected to find some fairly strong patterns. The population sizes for the different cell types should be similar. And if two different types of cell work together and perhaps are synaptically connected, then their cell counts should be correlated across the different strains. That is, if the count is a bit low for one of those cell types, then it should also be on the low side for the other type of cell.
But such patterns were not found. Instead the researchers were surprised to find all kinds of variability. The population sizes of the different cell types varied substantially with little correlation across the different strains.
The researchers also looked at which parts of the genome influence the population counts of the different cell types and concluded that multiple genes, acting differently in the different strains, are involved in specifying these population counts.
The study concluded that retinal assembly is far more flexible than thought. For instance, they concluded that the different retinal cells adjust their size and shape according to their local environment, including the density of the different types of cells around them.
What is emerging is a far more sophisticated retinal assembly process than was imagined. As one report summarized the study:
The circuitry of the central nervous system is immensely complex and, as a result, sometimes confounding. When scientists conduct research to unravel the inner workings at a cellular level, they are sometimes surprised by what they find.
Needless to say, this sort of variability between highly-related strains, and this level of sophistication and complexity, are inconsistent with evolutionary theory.