A versatile cryopreservation method for peri-gastrulation squamate embryos optimised using the veiled chameleon (C. calyptratus)

Stem cell technologies have become a vital component of conservation efforts around the globe. Biobanks and pluripotent stem cell lines help to ensure species and their genetic diversity are preserved. These efforts have however, focussed mostly on mammals and birds, and the cryopreservation protocols for embryos and cells were developed decades ago laying the basis for artificial reproductive techniques for species conservation. With over 20% of non-avian reptile species facing extinction, it is imperative to establish protocols for reptiles to ensure species preservation and also to facilitate the establishment of new reptile model organisms to match the standard of mammals. Here, we have generated a cryopreservation method for preserving early gastrulating veiled chameleon embryos as a representative squamate species. To this end, we first developed a tissue culture method for maintaining cells extracted from peri-gastrulation chameleon embryos and then tested different cryopreservation methods altering the concentration of the penetrating cryoprotectant DMSO and assessing the effect of the addition of non-penetrating cryoprotectants Trehalose and Sucrose. We then optimised a protocol for whole embryo vitrification in 20% DMSO with added Trehalose or Sucrose that can easily be adapted for fieldwork. Taken together, our method not only provides a protocol for conservation efforts but also lays the basis for mechanistic studies of early squamate embryo development by enabling cryopreservation of whole embryos in a fieldwork setting, which facilitates their live transport back to a laboratory for functional experiments or molecular analyses.