library_construction_protocol: Frozen embryos were homogenized using the Pellet Pestle Cordless Motor (Kimble Cat. No. 749540-0000; Pellet Pestles Sigma Cat. No. Z359947). RNA was extracted from the homogenate using TRIzol Reagent (Thermo Fisher, Cat. No. 15596026), chloroform extraction and isopropanol precipitation.  RNA was resuspended in Nuclease Free Water (Ambion AM9930) and incubated over night before purification using the RNeasy Mini Kit (QIAGEN Cat. No. 74106).  After Qiagen clean up, RNA was quantified using NanoDrop ND1000v 3.5.2. Libraries for sequencing were made using TruSeq Stranded mRNA Library Prep (llumina 20020594).