Allocation of inner cell mass and trophectoderm cells to the preimplantation blastocyst of the domestic ferret, Mustela putorius furo

The growth of ferret preimplantation blastocysts in vivo, collected between 156 and 240 hr post coitum, was investigated. A technique, combining immunosurgery and differential fluorochrome staining, was used to discriminate between inner cell mass (ICM) and trophectoderm (TE) cells. Using the stains propidium iodide and bisbenzimide (Hoechst 33342), the ICM was stained blue and the TE was stained pink. The ICM and TE counts for 90 blastocysts, respectively, averaged 25 and 63 at 156 hr and increased exponentially to 2077 and 4137 at 240 hr. The Box‐Cox procedure was used for choosing a transformation that minimized the error sum of squares for a linear regression of Y (cell count) on X (time in hr). Logarithmic transformations of the ICM, TE and total cell count gave a good fit, but the following equations obtained by the Box‐Cox procedure provided the best fit, where Y is cell count and X is time in hours. For inner cell mass: Ŷ = [(176.06 + 2.45X)/–899.44 + 1]–3.33; trophectoderm: Ŷ = [(301.38 + 14.48X)/–6863.42 + 1]–10 ; and total: Ŷ = [(2266.97 = 17.0X)/–7837.21 + 1]–5. The R2 values were 0.73, 0.84, and 0.84, respectively. The exponential growth of the ferret embryo during the time interval that measurements were made fits the general pattern described for other mammalian embryos. This report is the first to characterize the pattern of cell allocation and growth in preimplantation blastocysts of the ferret, and the first such report for a carnivore. The pattern of in vivo development provides a standard for judging the quality of in vitro produced and matured ferret embryos and, concomitantly, a means to evaluate culture systems. J. Exp. Zool. 283:202–209, 1999. © 1999 Wiley‐Liss, Inc.