A recent paper published showed why snakes are so long and have so many ribs- humans have 12 pairs, but some snakes have up to 400! This is due to a regulatory factor called Oct4, which controls spinal development and the number of ribs.
Oct4 is found in the anterior (head)- end of the trunk of developing vertebrate embryos, and is a pluripotency factor. This means it maintains stem cells, and prevents them from differentiating into a specific cell lineage.
Oct4 is normally inhibited by GDF11. However, a deleterious mutation in mice GDF11 prevents it from functioning properly. Therefore, Oct4 is no longer inhibited, and it acts further towards the anterior (bottom) end of the embryo. In mutant mice, this creates a longer spine and more pairs of ribs.
…but not in snakes
In snakes, the GDF11 gene is fully functional. So what makes Oct4 so special in snakes, that it can overcome the inhibitory power of this GDF11? The researchers expressed the snake Oct4 gene and its surrounding DNA regions in mice, and found that these mice also developed a very long spine and more ribs.
It turns out that the snake Oct4 function is determined by these regions of non-coding DNA around the gene. This DNA interacts epigenetically with the Oct4 gene. Epigenetics – the science behind non-coding DNA regulating the expression of coding genes- is a very popular area of research currently, as there are many things that are not yet understood about genetic control and regulation. This non-coding region of DNA changes the duration of Oct4 expression during development (the longer the expression, the longer the trunk!). This gives snakes the easily identifiable phenotype that we all recognise.
Why is this important?
There is still a lot to find out about epigenetics, and how non-coding DNA can control gene expression. Further understanding of the development of the spine and ribs in vertebrates could be beneficial towards understanding human anatomy and helping with genetic spinal problems. This also advances what we know about gene regulatory networks, and how genes interact with each other at different timings throughout development.
The paper: Aires et al. Oct4 is a Key Regulator of Vertebrate Trunk Length Diversity. 2016. DOI: http://dx.doi.org/10.1016/j.devcel.2016.06.021