Mitotic Implantation of the Transcription Factor Prospero via Phase Separation Drives Terminal Neuronal Differentiation

Dev Cell. 2020 Feb 10;52(3):277-293.e8. doi: 10.1016/j.devcel.2019.11.019. Epub 2019 Dec 19.


Compacted heterochromatin blocks are prevalent in differentiated cells and present a barrier to cellular reprogramming. It remains obscure how heterochromatin remodeling is orchestrated during cell differentiation. Here we find that the evolutionarily conserved homeodomain transcription factor Prospero (Pros)/Prox1 ensures neuronal differentiation by driving heterochromatin domain condensation and expansion. Intriguingly, in mitotically dividing Drosophila neural precursors, Pros is retained at H3K9me3+ pericentromeric heterochromatin regions of chromosomes via liquid-liquid phase separation (LLPS). During mitotic exit of neural precursors, mitotically retained Pros recruits and concentrates heterochromatin protein 1 (HP1) into phase-separated condensates and drives heterochromatin compaction. This establishes a transcriptionally repressive chromatin environment that guarantees cell-cycle exit and terminal neuronal differentiation. Importantly, mammalian Prox1 employs a similar "mitotic-implantation-ensured heterochromatin condensation" strategy to reinforce neuronal differentiation. Together, our results unveiled a new paradigm whereby mitotic implantation of a transcription factor via LLPS remodels H3K9me3+ heterochromatin and drives timely and irreversible terminal differentiation.

Keywords: Drosophila melanogaster; H3K9me3; HP1; Prospero/Prox1; heterochromatin condensation; liquid-liquid phase separation; mitotic retention; neural precursors; neural stem cells; neuronal differentiation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Differentiation*
  • Chromatin Assembly and Disassembly
  • Chromosomal Proteins, Non-Histone / genetics
  • Chromosomal Proteins, Non-Histone / metabolism*
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism*
  • Drosophila melanogaster / genetics
  • Drosophila melanogaster / growth & development*
  • Drosophila melanogaster / metabolism
  • Female
  • Gene Expression Regulation
  • Heterochromatin / genetics
  • Heterochromatin / metabolism*
  • Histones / genetics
  • Histones / metabolism
  • Liquid-Liquid Extraction
  • Male
  • Mitosis*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Neurons / cytology*
  • Neurons / metabolism
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Nucleosomes
  • Phase Transition*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*


  • Chromosomal Proteins, Non-Histone
  • Drosophila Proteins
  • Heterochromatin
  • Histones
  • Nerve Tissue Proteins
  • Nuclear Proteins
  • Nucleosomes
  • Transcription Factors
  • heterochromatin protein 1, Drosophila
  • pros protein, Drosophila