Researchers show fruit fly embryos follow precise, optimal development plan

An international research team discovered that a mathematically optimal model could predict the development pathway of a fruit fly (Drosophila) embryo and found that the embryo's decoding of gap gene expression data in its development closely approximates that of their optimal theoretical model. 

This study demonstrates that it is possible to make correct predictions about biological systems from theoretical principles.

The prevailing view is that the embryo's correct positioning develops over time in successive layers that correct for errors. In contrast the researchers show that the fruit fly embryo precisely decodes gap gene expression profiles that infer positional identity to cells from the beginning stage of the embryo.

The researchers were looking at the mechanisms involved in how the embryo precisely positions its legs, antennae and other body features, including the stripe pattern on its back. They found that the embryo used the available positional information in the optimal way out of many possible decoding strategies.

The research team was able to determine that cells in the embryo collect GPS-like packets of information so that they know their position in the embryo with an accuracy of 1%. The act of the cell knowing its position within the embryo allows for it to know if it should become a leg or a wing.

They created mutations in specific cells to cause defects in development and then used their mathematically optimal model to predict the embryos decoding of the defective information to determine where the defects would show up. Specifically, the researchers looked at the genes involved in the embryo responsible for the striped segmentation pattern.

This involves gap genes and pair-rule genes. Gap genes take their name from what happens if one of them has a defect that causes a "gap" in the usual body plan. Pair-rule genes are also defined by what happens when there is a mutation in the gene, changing the normal striped pattern.

The gap genes are pre-programmed by the genes of the mother fly, which embed signaling instructions in each egg. The four gap genes have a particular spatial pattern in the cell that encodes information. This information is decoded by enhancers and directs the pair-rule genes in the creation of the striped pattern.

The research showed not only that the fruit fly embryo decoded its genetic information precisely and optimally, but also that researchers could mathematically model the embryo's use of its coded information.

Drosophila are often used in biology as model systems because they multiply rapidly and have a short life cycle. Also about 60% of human genes are similar to those of fruit flies. 

The research work, carried out at Princeton University, appeared in the journal Cell, Feb. 7, 2019.

“The information required to specify precise cell locations--and therefore what body parts they will become--is present and utilized at the earliest stages of development in fruit flies. This contrasts with the prevailing view that the position of the cells is refined slowly over time," research team leader Thomas Gregor, associate professor of physics and the Lewis-Sigler Institute for Integrative Genomics, told the Princeton University News Office. “This research gives us a look at how genetic networks encode information, how networks work together and how they do the computations they can do. There are genetic networks that do all sorts of things in biology, so this is certainly a rich area for further exploration.”