Project description:Suppression of Meis genes in the distal limb bud is required for Proximal-Distal (PD) specification of the forelimb. Polycomb group (PcG) factors play a role in downregulation of retinoic acid (RA)-related signals in the distal forelimb bud, causing Meis repression. It is, however, not known if downregulation of RA-related signals and PcG-mediated proximal genes repression are functionally linked. Here, we reveal that PcG factors and RA-related signals antagonize each other to polarize Meis2 expression along the PD axis. With mathematical modeling and simulation, we propose that PcG factors are required to adjust the threshold for RA-related signaling to regulate Meis2 expression. Finally, we show that a variant Polycomb repressive complex 1 (PRC1), incorporating PCGF3 and PCGF5, represses Meis2 expression in the distal limb bud. Taken together, we reveal a previously unknown link between PcG proteins and downregulation of RA-related signals to mediate the phase transition of Meis2 transcriptional status during forelimb patterning.
Project description:Polycomb group (PcG) proteins play a pivotal role in epigenetically silencing development-related genes, restricting their expression to appropriate tissues. However, in some instances PcG target genes must also be dynamically regulated in response to developmental signals encountered during morphogenesis. Here we examine the role of PcG factors in early forelimb bud patterning, a process that relies on various morphogenetic signals. Depletion of Ring1 proteins, which are essential components of Polycomb repressive complex-1 (PRC1), led to dramatic deficiencies in forelimb formation and proximal-distal regionalization. Gene expression analysis identified Meis2 and Meis1 as critical PRC1 targets genes in early distal specification, with PcG proteins counteracting retinoic acid (RA) signaling to control their expression. Importantly, in this system, PcG factors appear to function by adjusting the threshold for RA signaling, revealing an unexpected role of polycomb proteins in dynamic gene regulation during development. [Affymetrix] Mouse E10.5 forelimb buds of Ring1A-KO, Ring1A/B-dKO and RA-treated wild type were used for RNA extraction and hybridization on Affymetrix microarrays. [Agilent] ChIP analysis of mouse E10.5 whole forelimb buds against anti-H3K27me3 antibody.
Project description:Polycomb group (PcG) proteins play a pivotal role in silencing developmental genes and help to maintain various stem and precursor cells and regulate their differentiation. PcG factors also regulate dynamic and complex regional specification, particularly in mammals, but this activity is mechanistically not well understood. In this study, we focused on proximal-distal (PD) patterning of the mouse forelimb bud to elucidate how PcG factors contribute to a regional specification process that depends on developmental signals. Depletion of the RING1 proteins RING1A (RING1) and RING1B (RNF2), which are essential components of Polycomb repressive complex 1 (PRC1), led to severe defects in forelimb formation along the PD axis. We show that preferential defects in early distal specification in Ring1A/B-deficient forelimb buds accompany failures in the repression of proximal signal circuitry bound by RING1B, including Meis1/2, and the activation of distal signal circuitry in the prospective distal region. Additional deletion of Meis2 induced partial restoration of the distal gene expression and limb formation seen in the Ring1A/B-deficient mice, suggesting a crucial role for RING1-dependent repression of Meis2 and likely also Meis1 for distal specification. We suggest that the RING1-MEIS1/2 axis is regulated by early PD signals and contributes to the initiation or maintenance of the distal signal circuitry. This SuperSeries is composed of the SubSeries listed below.
Project description:Polycomb group (PcG) proteins play a pivotal role in silencing of development-related genes and contribute to maintain various stem and precursor cells and regulate their differentiation. However, it is not well understood how PcG factors regulate dynamic and complex morphogenetic processes particularly in mammals. In this study, we focused on proximal-distal (PD) patterning of forelimb bud to elucidate how PcG factors contribute to regulation of morphogenetic processes that depends on developmental signals. Depletion of RING1 proteins, which are common components of both canonical and variant Polycomb repressive complex-1 (PRC1), led to dramatic deficiencies in forelimb formation. By using Ring1-deficient forelimb buds, we revealed the early defects in distal specification, which is due to the functional coupling of RING1 and retinoic acid (RA) signaling. RING1 activity is shown to antagonize with RA signals at Meis2 and likely Meis1, which are superior suppressors of distal formation program, in the prospective distal region of outgrowing forelimb bud. This study exhibits a first example showing how PcG factors interplay with developmental signals to mediate compartmentalization of elongating anlagen by regulating the expression of developmental genes.
Project description:Polycomb group (PcG) proteins play a pivotal role in silencing of development-related genes and contribute to maintain various stem and precursor cells and regulate their differentiation. However, it is not well understood how PcG factors regulate dynamic and complex morphogenetic processes particularly in mammals. In this study, we focused on proximal-distal (PD) patterning of forelimb bud to elucidate how PcG factors contribute to regulation of morphogenetic processes that depends on developmental signals. Depletion of RING1 proteins, which are common components of both canonical and variant Polycomb repressive complex-1 (PRC1), led to dramatic deficiencies in forelimb formation. By using Ring1-deficient forelimb buds, we revealed the early defects in distal specification, which is due to the functional coupling of RING1 and retinoic acid (RA) signaling. RING1 activity is shown to antagonize with RA signals at Meis2 and likely Meis1, which are superior suppressors of distal formation program, in the prospective distal region of outgrowing forelimb bud. This study exhibits a first example showing how PcG factors interplay with developmental signals to mediate compartmentalization of elongating anlagen by regulating the expression of developmental genes.
Project description:Polycomb group (PcG) proteins play a pivotal role in silencing of development-related genes and contribute to maintain various stem and precursor cells and regulate their differentiation. However, it is not well understood how PcG factors regulate dynamic and complex morphogenetic processes particularly in mammals. In this study, we focused on proximal-distal (PD) patterning of forelimb bud to elucidate how PcG factors contribute to regulation of morphogenetic processes that depends on developmental signals. Depletion of RING1 proteins, which are common components of both canonical and variant Polycomb repressive complex-1 (PRC1), led to dramatic deficiencies in forelimb formation. By using Ring1-deficient forelimb buds, we revealed the early defects in distal specification, which is due to the functional coupling of RING1 and retinoic acid (RA) signaling. RING1 activity is shown to antagonize with RA signals at Meis2 and likely Meis1, which are superior suppressors of distal formation program, in the prospective distal region of outgrowing forelimb bud. This study exhibits a first example showing how PcG factors interplay with developmental signals to mediate compartmentalization of elongating anlagen by regulating the expression of developmental genes.
Project description:Polycomb group (PcG) proteins play a pivotal role in epigenetically silencing development-related genes, restricting their expression to appropriate tissues. However, in some instances PcG target genes must also be dynamically regulated in response to developmental signals encountered during morphogenesis. Here we examine the role of PcG factors in early forelimb bud patterning, a process that relies on various morphogenetic signals. Depletion of Ring1 proteins, which are essential components of Polycomb repressive complex-1 (PRC1), led to dramatic deficiencies in forelimb formation and proximal-distal regionalization. Gene expression analysis identified Meis2 and Meis1 as critical PRC1 targets genes in early distal specification, with PcG proteins counteracting retinoic acid (RA) signaling to control their expression. Importantly, in this system, PcG factors appear to function by adjusting the threshold for RA signaling, revealing an unexpected role of polycomb proteins in dynamic gene regulation during development.
Project description:Vertebrate limbs develop by integrating signals that control patterning along three main orthogonal axes. Flank-produced retinoic acid (RA) is initially required for limb induction and establishment of the apical ectodermal ridge (AER), a distal signaling center that produces fibroblast growth factors (FGFs), which are essential for limb growth and distalization. Once the AER is established, RA:FGF antagonism determines the restricted expression of a set of genes that control limb proximodistal patterning. Essential for this antagonism is the activation by FGF of the RA-degrading enzyme CYP26B1 in the distal limb bud. In addition, sonic hedgehog produced from the zone of polarizing activity (ZPA) is essential for distal limb anteroposterior patterning and contributes to RA reduction by cooperating in CYP26B1 activation. Meis transcription factors are expressed in the proximal limb bud, are activated by RA and can regulate proximodistal limb development; however, the mechanisms underlying their activity remain unknown. Here we studied Meis function in the mouse limb bud through Meis2 conditional overexpression and elimination of Meis1 and Meis2. We found that Meis activity is first required for limb bud initiation and the proper establishment of the AER and ZPA signaling centers, and subsequently for the development of proximal limb structures. Functional genomic analyses reveal that Meis is an important conveyor of the RA:FGF antagonism through the regulation of components of the RA and FGF signaling pathways, including CYP26B1. In addition, Meis regulates a set of proximal limb genes controlling proximodistal patterning and differentiation. Our work reveals a regulatory module essential for limb patterning and potentially co-opted in other patterning processes involving RA:FGF antagonism.
Project description:To investigate into the evolutionary conversation of the single-cell transcriptome of human fetal limbs, especially the principles of forelimb and hindlimb specification and proximal-distal axis establishment, we collected the forelimbs and hindlimbs of mouse embryos matching human samples. We dissected the limbs to separate proximal, middle and distal parts and generated single-cell RNA-seq data of more than 70,000 cells. Combining this dataset with our human data, we are able to see highly conserved limb cell types and limb axis drivers.