Abstract

The 13-lined ground squirrel (Ictidomys tridecemlineatus; 13LGS) has excellent daytime vision based on numerous cone photoreceptors in their retinas; a human-like lens and eye structure; and a markedly larger portion of occipital cortex devoted to visual inputs. Therefore, the 13LGS has been identified by the National Eye Institute as a valuable alternative rodent model for studying treatments of human visual disease.

In addition, the 13LGS is an invaluable model for exploring possible translation of its hypometabolic hibernation physiology to various aspects of human medicine, including blood banking, emergency brain and cardiac care, and manned spaceflight. Despite all these advantages of the 13LGS for multiple fields of biomedical research, the species’ embryonic and fetal development over ~27 days’ gestation remains undescribed.

This project tested the hypothesis that the Theiler Staging criteria established for laboratory mice can be applied to the 13LGS.

Multiple pre-implantation embryos (collected 1-4 days post-copulation), 16 fetuses, and 1 neonate were collected from UW Oshkosh Squirrel Colony specimens over several years and preserved. Using a dissecting microscope, their crown-rump measurements and gross anatomical features corresponding to Theiler Stating were documented.

The available pre-implantation embryos were found to span TS1-4, whereas the available fetuses spanned TS16-26. The neonatal specimen constituted TS27. The species’ characteristic stripe/spot pattern was visible in the skin by embryonic day 21, corresponding to TS24. To capture TS5-15, additional 13LGS specimens must be collected in future breeding seasons, but the images reported here represent about two-thirds of this useful model species’ prenatal development.

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