show Abstracthide AbstractA biochemical explanation of development from the fertilized egg to the adult anatomy requires an understanding of the complement of proteins and RNAs expressed over time during embryogenesis. Here we present a comprehensive characterization of protein and mRNA dynamics across early development in Xenopus. Surprisingly, we find that most proteins change very little and duplicated genes are expressed similarly. While the correlation between mRNA levels and protein expression is poor, a mass action kinetics model parametrized by the protein synthesis and degradation rates regresses protein dynamics to RNA dynamics, corrected for initial protein concentration. This study provides a rich resource for developmental biologists, unveiling detailed data for absolute levels of ~10K proteins and ~28K transcripts via convenient web portal. It underscores the lasting impact of maternal dowry, finds surprisingly few cases where degradation alone drives a change in protein level, and highlights the importance of transcription in shaping the proteome. Overall design: mRNA from 18 samples each at a different developmental stage. Libraries were constructed using RNA enriched for mRNA by Poly(A) extraction using Dynabeads (invitrogen) and the EpiCenter ScripSeq kit V1 using 50-300ng input RNA, and 10 cycles amplification.