Mammalian genomes are partitioned into domains that replicate in a defined 
temporal order. These domains can replicate at similar times in all cell types 
(constitutive) or at cell type-specific times (developmental). Genome-wide 
chromatin conformation capture (Hi-C) has revealed sub-megabase topologically 
associating domains (TADs), which are the structural counterparts of replication 
domains. Hi-C also segregates inter-TAD contacts into defined 3D spatial 
compartments that align precisely to genome-wide replication timing profiles. 
Determinants of the replication-timing program are re-established during early 
G1 phase of each cell cycle and lost in G2 phase, but it is not known when TAD 
structure and inter-TAD contacts are re-established after their elimination 
during mitosis. Here, we use multiplexed 4C-seq to study dynamic changes in 
chromatin organization during early G1. We find that both establishment of TADs 
and their compartmentalization occur during early G1, within the same time frame 
as establishment of the replication-timing program. Once established, this 3D 
organization is preserved either after withdrawal into quiescence or for the 
remainder of interphase including G2 phase, implying 3D structure is not 
sufficient to maintain replication timing. Finally, we find that developmental 
domains are less well compartmentalized than constitutive domains and display 
chromatin properties that distinguish them from early and late constitutive 
domains. Overall, this study uncovers a strong connection between chromatin 
re-organization during G1, establishment of replication timing, and its 
developmental control.