A mathematical model of in vivo bovine blastocyst developmental to gestational Day 15

Abstract

Bovine embryo growth involves a complex interaction between the developing embryo and the growth-promoting potential of the uterine environment. We have previously established links between embryonic factors (embryo stage, embryo gene expression), maternal factors (progesterone, body condition score), and embryonic growth to 8 d after bulk transfer of Day 7 in vitro-produced blastocysts. In this study we recovered blastocysts on Days 7 and 15 after artificial insemination to test the hypothesis that in vivo and in vitro embryos follow a similar growth program. We conducted our study using 4 commercial farms and repeated our study over 2 yr (2014, 2015), with data available from 2 of the 4 farms in the second year. Morphological and gene expression measurements (196 candidate genes) of the Day 7 embryos were measured and the progesterone concentration of the cows were measured throughout the reproductive cycle as a reflection of the state of the uterine environment. These data were also used to assess the interaction between the uterine environment and the developing embryo and to examine how well Day 7 embryo stage can be predicted from the Day 7 gene expression profile. Progesterone was not a strong predictor of in vivo embryo growth to Day 15. This contrasts with a range of Day 7 embryo transfer studies which demonstrated that progesterone is a very good predictor of embryo growth to Day 15. Our analysis demonstrates that in vivo embryos are 3 times less sensitive to progesterone than in vitro-transferred embryos (up to Day 15). This highlights that caution must be applied when extrapolating the results of in vitro embryo transfer studies to the in vivo situation. The similar variance in measured and predicted (based on Day 15 length) Day 7 embryo stage indicate low stochastic perturbations for in vivo embryo growth (large stochastic growth effects would generate a significantly larger standard deviation in measured embryo length on Day 15). We also identified that Day 7 embryo stage could be predicted based on the Day 7 gene expression profile (58% overall success rate for classification of 5 embryo stages). Our analysis also associated genes with each developmental stage and demonstrates the high level of temporal regulation of genes that occurs during early embryonic development.

Embryo development and survival in peripubertal ewe lambs

“…Therefore, the single sample collected at the time of embryo collection in the Day 14 group in the present study may not have been sufficient to observe relationships between progesterone concentrations and conceptus length. In addition, the relationship between progesterone concentrations and length of the conceptus on Day 15 of pregnancy was much weaker when examined in bovine embryos that were developed in vivo following artificial insemination (Shorten et al 2018b) than in embryos produced in vitro and transferred to the uterus on Day 7; this is more consistent with our study, where no correlation was observed on Day 14 following natural mating. Changes in other steroids may also regulate conceptus length.…”

Symposium review: Selection for fertility in the modern dairy cow—Current status and future direction for genetic selection

“…There is also the potential for bacterial toxins arising from the diseased uterus to cause inflammation within the ovary and reduce oocyte competence (Bromfield et al, 2015;Ribeiro et al, 2016). Shorten et al (2018) reported that approximately 65% of inseminated dairy cows had a viable embryo 1 wk after AI (Shorten et al, 2018). The low percentage of pregnant cows 1 wk after AI is perhaps explained by a low-quality oocyte with fertilization failure or poor developmental competence within the oviduct during the first week after AI.…”

FABP4 mediates endoplasmic reticulum stress and autophagy to regulate endometrial epithelial cell function during early sheep gestation

“…IFN-τ is a pregnancy recognition signal that acts on the endometrium to maintain the continuous production of P4 by the ovaries. Additionally, it regulates the genes related to embryonic implantation and growth [11,12]. During pregnancy, the endometrium and embryos of sheep produce prostaglandins including prostaglandin F2α(PGF2α) and prostaglandin E2(PGE2).…”