The success of any investigation of developing embryos relies on an ability to see developmental processes unfolding. As embryos are microscopic, three-dimensional, complex, delicate, often transparent, and constantly changing, seeing their development has long presented embryologists with fascinating visualization challenges. Devising methods for seeing them is a highly creative act that involves experimentation and the production of various representations and modes of analyzing them.

To explore how we see developing embryos, both historically and in the modern day, I investigated Edwin Grant Conklin’s 1897 cell lineage study of embryos of the marine slipper limpet Crepidula fornicata. In this study, Conklin followed almost every cell division from the fertilized egg all the way to the larval stage to show that entire tissue types and organs can be traced back to individual cells in the early embryo, a remarkable feat in observation and meticulous note-taking. For Conklin, seeing this developmental process required an intensive process that involved myriad materials, instruments, skills, and images. Furthermore, images were not only the most effective way to communicate his work, but drawings and sketches played a central role in his ability to see Crepidula embryos in the first place. 

To better understand Conklin's process and how visualization technologies shape how we see embryogenesis, I reconstructed Conklin's study of Crepidula embryos, both using his methods and modern ones. The main techniques Conklin used for studying cell lineage involved fixing and staining embryos and then drawing and sketching them with a camera lucida. Today, we can microinject individual blastomeres with lineage tracing proteins and dyes, perform antibody staining, photograph and live-image embryos, and even create interactive virtual reality and 3D-printed models. 

Above: Sketching from Conklin's Crepidula embryo slides (see photographs at top for examples of the embryos on these slides) with a camera lucida at the Marine Biological Laboratory in Woods Hole, MA. Below: Crepidula and their embryos in the lab.

3D-printed models of a 24-cell stage Crepidula embryo. Modeled from a z-stack of confocal microscope images. 

3D-printed models of a 24-cell stage Crepidula embryo. Modeled from a z-stack of confocal microscope images. 

 

An article and accompanying video featuring this project (by Hyacinth Empinado at STAT News) were published in STAT and Scientific American on February 22nd, 2017.