How do avian embryos resume development following diapause? A new role for TGF-β in regulating pluripotency-related genes

Avian embryos can halt their development for long periods at low temperature in a process called diapause and successfully resume development when reincubated at maternal body temperature. Successful resumption of development depends on different factors, including temperature. We have recently shown that embryos that enter diapause at 18 {degrees}C present a significant reduction in their ability to develop normally when put back into incubation, compared to embryos entering diapause at 12 {degrees}C. However, the mechanisms underlying these differences are unknown. To address this question, transcriptome analysis was performed to compare the effect of diapause temperature on gene expression, and to identify pathways involved in the process. Genetic comparison and pathway-enrichment analysis revealed that TGF-{beta} and pluripotency-related pathways are differentially regulated at the two temperatures, with higher expression at 12 {degrees}C compared to 18 {degrees}C. Investigating the involvement of the TGF-{beta} pathway revealed an essential role for BMP4 in regulating the expression of the transcription factors Nanog and Id2, which are known to regulate pluripotency and self-renewal in embryonic stem cells. BMP4 gain- and loss-of-function experiments in embryos in diapause at the different temperatures revealed the main role of BMP4 in enabling resumption of normal development following diapause. Collectively, these findings identify molecular regulators that facilitate embryos ability to undergo diapause at different temperatures and resume a normal developmental program.