Is the Primary Cilium a Cell’s Antenna or Its Brain

Excerpt: “With the primary cilium at the center of cellular sensation, communication, movement, cell division, autophagy and decision making, it is clearly a hub of purposeful behavior in all cells including the neuron. Is it possible that the primary cilium is the brain of the cell?”

My comment: At the advent of sexual reproduction in yeasts, a cilium-like projection forms on one cell that enables two cells of different types (e.g., male and female) to stick together and exchange genetic material. The development of the different cell types is nutrient-dependent and pheromone-controlled and so is their sexual orientation.

The molecule that enables the exchange of genetic material is so similar to a GnRH molecule of mammals that it elicits an LH response from the cultured pituitary cells of the rat. In mammals and other vertebrates, differences in the pulsatile secretion of GnRH secretion enable the brain’s response to food odors and pheromones.

Thanks to Jon, we now have information on how differences in morphology may link the cilia of unicellular organisms to human brain development via conserved molecular mechanisms, which also link the epigenetic landscape via chemical sensation (e.g., “smelling”) to the physical landscape of DNA in the organized genome of species from microbes to man. Indeed, Lewis Thomas once wrote: “The act of smelling is remarkably like the act of thinking itself.”

Like Jon Lieff, Lewis Thomas may also have linked the brain of the cell to the human brain. Unlike Jon Lieff, Lewis Thomas was not familiar with the extant literature, which has only recently become available. Thus, we have Jon to thank for keeping us up-to-date.

Olfactory receptor cells have dendrites instead of cilia, and they are equipped with receptors for all sorts of chemical stimuli. The de novo creation of olfactory receptor genes in olfactory receptor neurons appears to link nutrient-dependent amino acid substitutions to differences in cell types of individuals and species in species from microbes to man. It is those differences that globally enable nutrient uptake and the metabolism of nutrients to species-specific pheromones that control the physiology of reproduction. Thus, the primary cilium of most cell types can be linked to the diversification of most, if not all, species that sexually reproduce.

Alternatively, mutations may be responsible for sex differences and the ecological, social, neurogenic, and socio-cognitive niche construction that is exemplified by species diversity and by organismal complexity. However, it seems to make more sense to think in terms of conserved molecular mechanisms, as Jon does, even if others must start by thinking about the primary cilium as the brain of the cell.