Fertilization triggers early proteomic symmetry breaking in mammalian embryos
Lisa K. Iwamoto-Stohl, Aleksandra A. Petelski, Baiyi Quan, Maciej Meglicki, Audrey Qiuyan Fu, Shoma Nakagawa, Breanna McMahon, Tingyu Wang, Saad Khan, Harrison Specht, Gray Huffman, Jason Derks, Sergi Junyent, Bailey A. T. Weatherbee, Antonia Weberling, Carlos W. Gantner, Rachel S. Mandelbaum, Richard J. Paulson, Lisa Lam, Tsui-Fen Chou, Nikolai Slavov, Magdalena Zernicka‐Goetz
Abstract
While non-mammalian embryos often rely on spatial pre-patterning, mammalian development has long been thought to begin with equivalent blastomeres. However, emerging evidence challenges this. Here, using multiplexed and label-free single-cell proteomics, we identify over 300 asymmetrically abundant proteins-many involved in protein degradation and transport-dividing mouse 2-cell-stage blastomeres into two distinct clusters, which we term alpha and beta. These proteomic asymmetries are detectable as early as the zygote stage, intensify by the 4-cell stage, and correlate with the sperm entry site, implicating fertilization as a symmetry-breaking event. Splitting 2-cell-stage embryos into halves reveals that beta blastomeres possess greater developmental potential than alpha blastomeres. Similar clustering and protein enrichment patterns found in human 2-cell embryos suggest this early asymmetry might be conserved. These findings uncover a previously unrecognized proteomic pre-patterning triggered by fertilization in mammalian embryos, with important implications for understanding totipotency and early lineage bias.