Opening the Black Box of Late Neurodevelopment

“There's some reason to think that the earliest behaviors and the earliest circuits may have an outsized role overall in neurodevelopment and that what happens earliest on can have enduring effects on the developmental outcome at the individual,” says co-author Joshua Kaplan, professor at Harvard Medical School and Massachusetts General Hospital. 

The team discovered that early on, the embryo repeatedly flips over and then slows down its motion before showing mature, adult-like motion in the last phase of embryogenesis. During the phase right before hatching, embryos begin crawling, moving forward and backward, and, importantly, going through rhythmic patterns of rest. The authors termed this sleep-like behavior “slow wave twitch (SWT)”. 

This is the first paper to fully map out the movements happening in the last few hours of embryonic development in C. elegans and show a rhythmic, sleep-like state within that time period. Going forward, the team hopes to understand the function of SWT in aiding either development or neural circuit functioning.
 

Imaging Challenges and Solutions

C. elegans embryos are very delicate and sensitive to light, which creates a challenge for microscopy. When put under too much light, they arrest and stop developing, so many scientists, including senior author and MBL Fellow Hari Shroff, have adopted and developed light-sheet fluorescence microscopes (LSFM) that can image samples rapidly and gently while still capturing the whole 3D sample.

While LSFM and fluorescent markers on the sides of the developing animal, in principle, allow scientists to monitor its posture as it grows, tracking various parts of the animal during rapid embryo movement was still a challenge. 

Andrew Lauziere, co-first author, NIH Intramural Research Fellow and graduate student at University of Maryland, used the different points along what he calls a “little motion capture suit” on the embryo to build improved tracking software. Some parts of the animal move together, an assumption that allowed the modeling of movement to be more accurate than assuming independent movement. Still challenging to model are the animal’s fast jerks, which the imaging rate is not quite quick enough to capture, but the new computational tool Lauziere developed allows scientists to visualize and manually correct errors from automated tracking.

“One new technical contribution here was the development of a tracking framework that simultaneously accounted for correlated embryo movements, incorporated the animal anatomy, and permitted manual correction of errors caused by embryo jerking movements,” says Shroff, senior investigator at NIH at the time of the work and currently Senior Group Leader at Janelia Research Campus.