'How organisms convert 2D patterns into 3D'

Hosts: Prof Kees Weijer & Prof Rastko Sknepnek

Venue: MSI Small Lecture Theatre, SLS

Abstract

The question "How are organisms formed?" is one of the central questions in developmental biology. In the past 30 years, embryological experiments and mathematical modeling studies have revealed the mechanisms by which individual genes are expressed in specific regions, the so-called principles of pattern formation. However, most of these principles deal only with the division of a two-dimensional fixed field into regions. In actual morphogenetic phenomena, however, pattern formation and field expansion and deformation proceed simultaneously. Because it is extremely difficult to mathematically model or simulate such a complex phenomenon in which two or more different elements affect each other, the 3D morphogenesis of organisms is still not well understood to this day.

However, let us change our thinking a bit here. The fact that it is difficult to simulate a phenomenon in which a large number of elements affect each other should mean that such a system should not work well in a real organism. Put another way, for the stable progression of actual morphogenesis, it should be more convenient for the patterning, expansion, and deformation elements to occur on different time schedules so that they do not affect each other. In fact, there are examples of complex forms produced in such a manner.

Adult Japanese beetles have large, very intricately shaped horns, which are not present during the larval stage, but appear suddenly when the beetle metamorphoses into a pupa. Horn precursors are present in the head of the larva. The precursor is made up of a single cell layer, but has a complex pattern of wrinkles. During the molt to pupa, the larva uses the pressure of body fluids to stretch the wrinkles like a balloon being inflated, resulting in the instantaneous appearance of a huge horn. Since the wrinkles in the precursor are basically uniform in spacing and depth, once the wrinkle pattern is determined, the 3D morphology when inflated will be determined. In other words, this system can create complex 3D forms from simple 2D patterns.

In my seminar, I will explain in detail the 3D morphogenetic technique of this beetle. I will also introduce organisms that produce complex morphology using methods quite different from this beetle's method. Please stay tuned.