Northwestern Medicine scientists have uncovered new details about how the spinal column forms in developing vertebrates, according to a study published in Developmental Cell.
While it has been understood that the development and segmentation of the vertebral column are controlled by oscillations in proteins and intercellular communication signals, the exact mechanisms underlying vertebral segmentation have remained mysterious.
The new findings will help scientists better understand how the spinal column develops and may inform therapies for congenital scoliosis, according to Ertuğrul Özbudak, PhD, the Robert Laughlin Rea Professor of Anatomy and senior author of the study.
Previous research from the Özbudak laboratory found that vertebral column segmentation involved two sets of molecular players: the first functions as a “clock,” controlling how frequently somites — embryonic precursors to the vertebral column — form. The second acts as a kind of molecular “knife,” deciding where to place the borders between somites.
“We found that these two molecular pathways are the key to how segment borders and numbers are specified in vertebrates,” said Özbudak, who is also professor of Cell and Developmental Biology.
In the current study, the scientists analyzed how the vertebral columns of zebrafish form in an effort to better understand how the different pathways interact.
First, investigators performed bimolecular fluorescence complementation assays to observe protein interactions in developing vertebrae embryos. They found that the “clock” proteins – Her1 and Her7 – directly interact with the phosphatase proteins Dusp4 and Dusp6.
Next, investigators inhibited the phosphatase activity of the Dusp proteins. They found that levels of phosphorylated ERK kinase did not oscillate as expected, and the zebrafish somites did not form proper boundaries.
“In this study, we have discovered the molecular link between the segmentation clock transcription factors and the ERK kinase, which is the molecular knife controlling segment boundary position,” Özbudak said. “These transcription factors have a so far unnoticed novel function: a post-translational function. They physically interact with the Dusp class of phosphatases and during this physical interaction, they stabilize those phosphatases and those phosphatases dephosphorylate and thereby inhibit the activity of the ERK kinase.”
The findings demonstrate that interactions between the two sets of proteins establish the fundamental body blueprint for vertebrates, Özbudak said. The results of the study also show that the two sets of molecular players can be altered via pharmaceutical means, which may be helpful in the future as scientists develop therapies for congenital scoliosis.
“The more we learn about the molecular missing links in between this process, the better the understanding of the cause and etiology of birth defects,” Özbudak said.
Moving forward, Özbudak will continue to study the unique protein interactions that regulate the development of important organs and tissues.
“We are trying to find out structurally how these molecules interact with each other,” Özbudak said. “What do they do to each other when they interact? Are there others that so far we’ve been missing from the picture? Those are the questions we’ll be following up.”
The study was funded by National Institutes of Health grant R01HD103623.