Self-reference, closed circuits and the phototactic sensorimotor mechanism of the unicellular alga Euglena gracilis. An application to the study of nonlinear dynamics in microtubular structures

Contemporary biology still lacks a model capable of accounting for even the most basic phenomena involving microtubules (MT) such as for example intracellular transport and ciliary beating, not to speak of the function of MT in sensory and nerve cells.

As an example, vertebrate photoreceptors contain a cilium whose dynamic function is still unknown.

A new model of microtubular dynamics, developed by the author together with P. Zaborski and J. Tuszynski (Insinna et al., 1996) and based on classical nonlinear physics, is capable of accounting for most of the phenomena associated with cell motility.

Additionally, its heuristic capabilities contribute to shed a new light not only on the phototactic behavior of the Protozoan Euglena gracilis but also on the dynamic role of MT in vertebrate photoreceptors and their specific responses.

Some unicellular organisms such as Euglena gracilis display in fact simple perceptive functions (phototaxis) which imply the use of a primitive photoreceptor.

This unicellular offers the unique possibility to study the function of MT in simple forms of vision, laying ahead of the complexity of more sophisticated photoreceptor systems.

Euglena gracilis appears to be the prototype of a self-referential, dynamical sensory system, whose study might allow us to understand the evolution of more complex perceptive systems.