Early mouse development seen in real time
Posted by Heather Ray, on 15 January 2013
Developmental biologists have long relied on the power of observation to understand how embryos develop. In addition, pharmacologic and genetic manipulation of embryos gives us clues as to the mechanisms involved in proper developmental processes. The ability to combine embryo manipulation with observation of embryonic development in real time has been possible for quite some time when using model organisms that develop externally, such as chicks, frogs and zebrafish. However, for those of us that use a mammalian model system, the technology to observe development in real time has lagged way behind. How we long for a way to watch organ systems develop and cell populations migrate and differentiate in the early embryo. While we have many sophisticated genetic tools to study these types of processes, we are limited to looking at simple “snapshots” of time based on when the embryos are dissected and fixed. The task of generating a robust confocal microscopy-based live imaging platform for early mouse embryos was taken on by R’ada Massarwa, a post-doc in the Niswander lab and the culmination of this work was recently published in Development (2013 Jan;140(1):226-36).
During the creation of this live imaging system, she chose to observe the process of neural tube closure, which occurs between days 8.5 and 10.0 of embryonic growth (E8.5-E10.0) in the mouse. Following dissection and experimental setup, the embryos are able to survive up to 16 hours of live imaging. Thus, by performing a series of experiments in which embryos were dissected at increasing somite stages, the entire process of neural tube closure was observed. This type of careful sequential experimentation also showed that the culture and imaging system did not interfere with the proper growth and movement of the tissues. The result: beautiful movies that not only show us how the neural tube develops, but also highlight all the exciting possibilities that this system brings to the study of early mammalian development.
We have been using this system to study neural tube closure, but there are many other tissues and organs that develop during these time periods (E8.5-E10.5) that are amenable to imaging including the heart, face, limbs and neural crest. By using tissue-specific Cre- recombinase reporter strains, the behavior of individual cell types can now be observed in real time in the early mammalian embryo. Also, combining fluorescent reporter strains with genetic knock-out strains and imaging the mutant embryos as the phenotype begins and progresses can provide a much better understanding of how the loss of gene function affects a developmental process. This system also provides access to the embryo itself for pharmacologic and physical manipulation. Overall, the potential for what can be learned using this live embryo imaging system is incredible. We are excited to share this technology with the scientific community and we look forward to seeing how all of you are able to use it to your advantage. Happy imaging!
Massarwa R. & Niswander L. (2012). In toto live imaging of mouse morphogenesis and new insights into neural tube closure, Development, 140 (1) 226-236. DOI: 10.1242/dev.085001
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