The spiny mouse (Acomys cahirinus), is a unique rodent species in which offspring (1-4 pups) of precocial nature are born after a relatively long pregnancy (39 days). Their precocity at birth has facilitated the use of the spiny mouse as an animal model for perinatology, however investigations into fertilisation, zygote cleavage and the early development of the spiny mouse embryo have not yet been conducted. This study describes and compares the in vivo pre-implantation development of the spiny mouse embryo with the normal mouse embryo (F1 hybrid) across the first 5 days of pregnancy.

We recovered embryos from naturally mated females at 12 hrly intervals, assessed stage of development and conducted measures of embryo dimensions such as whole embryo diameter, blastomere diameter, cell mass diameter and zona pellucida thickness at each developmental stage.

Delayed embryo development was observed for the spiny mouse when compared to the F1 mouse, however spiny mouse patterns of development more closely reflect that of the human embryo reported in the literature. The spiny mouse has a prolonged 4-8 cell stage which we hypothesise may coincide with the timing of embryonic genome activation in this species. The spiny mouse was also found to be significantly smaller than the F1 mouse in all embryo dimension parameters except zona pellucida thickness, which was significantly thicker for the spiny mouse. Interestingly, the ratio of zona pellucida thickness to embryo cell mass for the spiny mouse closely reflected that ratio for the human embryo.

Our study has highlighted several differences between spiny mouse and normal mouse preimplantation development, but noted some characteristics of the spiny mouse embryo, which may be useful in the study of human embryo development.