Project description:Hindlimb and Forelimb-specific Tbox factors integrates their mode of action with distinct Hox factors resulting in different transcriptional outcomes. In addition, hindlimb-specific Tbx4, Hoxc10 and Pitx1 act on the same platform to target common putative downstream genes for hindlimb development
Project description:Development of the complex structure of the vertebrate limb requires carefully orchestrated interactions between multiple regulatory pathways and proteins. Among these, precise regulation of 5’ Hox transcription factor expression is essential for proper limb bud patterning and development. Here, we identified Geminin (Gmnn) as a novel regulator of this process. A conditional model of Gmnn deficiency resulted in loss or severe reduction of forelimb skeletal elements, while both the forelimb autopod and hindlimb were unaffected. 5’ Hox gene expression expanded into more proximal and anterior regions of embryonic forelimb buds in this Gmnn-deficient model. A second conditional model of Gmnn deficiency instead caused a similar but less severe reduction of hindlimb skeletal elements and hindlimb polydactyly, while not affecting the forelimb. An ectopic posterior Shh signaling center was evident in the anterior hindlimb bud of Gmnn-deficient embryos in this model. This center ectopically expressed Hoxd13, the Hoxd13 target Shh, and the Shh target Ptch1, while these mutant hindlimb buds also had reduced levels of the cleaved, repressor form of Gli3, a Shh pathway antagonist. Together, this work delineates a new role for Gmnn in modulating Hox expression to pattern the vertebrate limb.
Project description:During embryonic development, fields of progenitor cells form complex spatial structures through dynamic interactions with external signaling molecules. However, how complex signaling inputs are integrated to yield appropriate gene expression responses is poorly understood. For instance several critical signals have been well characterized in the early limb bud, including Sonic hedgehog (Shh) and Fibroblast growth Factor 8 (Fgf8). While the former is expressed in the distal posterior mesenchyme where it acts as the mediator of anterior to posterior (AP) patterning, the latter is produced by the apical ectodermal ridge (AER) at the distal tip of the limb bud and directs the outgrowth and the proximal to distal (PD) organization of the limb. Here we use cultured limb mesenchyme cells to try and assess the response of the target Hoxd genes to these two factors. We find that they act synergistically and that both factors are required to get activation of Hoxd13 in limb mesenchymal cells. However, the analysis of the enhancer landscapes flanking the HoxD cluster reveals that the bimodal regulatory switch observed in vivo is not fully achieved under these in vitro conditions, suggesting the requirement for other factors.
Project description:During embryonic development, fields of progenitor cells form complex spatial structures through dynamic interactions with external signaling molecules. However, how complex signaling inputs are integrated to yield appropriate gene expression responses is poorly understood. For instance several critical signals have been well characterized in the early limb bud, including Sonic hedgehog (Shh) and Fibroblast growth Factor 8 (Fgf8). While the former is expressed in the distal posterior mesenchyme where it acts as the mediator of anterior to posterior (AP) patterning, the latter is produced by the apical ectodermal ridge (AER) at the distal tip of the limb bud and directs the outgrowth and the proximal to distal (PD) organization of the limb. Here we use cultured limb mesenchyme cells to try and assess the response of the target Hoxd genes to these two factors. We find that they act synergistically and that both factors are required to get activation of Hoxd13 in limb mesenchymal cells. However, the analysis of the enhancer landscapes flanking the HoxD cluster reveals that the bimodal regulatory switch observed in vivo is not fully achieved under these in vitro conditions, suggesting the requirement for other factors.
Project description:Vertebrate appendage patterning is programmed by Hox-TALE factors-bound regulatory elements. However, it remains enigmatic which cell lineages are commissioned by Hox-TALE factors to generate regional specific pattern and whether other Hox-TALE co-factors exist. In this study, we investigated the transcriptional mechanisms controlled by the Shox2 transcriptional regulator in limb patterning. Harnessing an osteogenic lineage-specific Shox2 inactivation approach we show that despite widespread Shox2 expression in multiple cell lineages, lack of the stylopod observed upon Shox2 deficiency is a specific result of Shox2 loss of function in the osteogenic lineage. ChIP-Seq revealed robust interaction of Shox2 with cis-regulatory enhancers clustering around skeletogenic genes that are also bound by Hox-TALE factors, supporting a lineage autonomous function of Shox2 in osteogenic lineage fate determination and skeleton patterning. Pbx ChIP-Seq further allowed the genome-wide identification of cis-regulatory modules exhibiting co-occupancy of Pbx, Meis, and Shox2 transcriptional regulators. Integrative analysis of ChIP-Seq and RNA-Seq data and transgenic enhancer assays indicate that Shox2 patterns the stylopod as a repressor via interaction with enhancers active in the proximal limb mesenchyme and antagonizes the repressive function of TALE factors in osteogenesis. RNA sequencing profiling the transcriptome of Shox2+ in the developing limb
Project description:Meis1 and Meis2 are highly similar homeodomain transcription factors that regulate organogenesis through cooperation with Hox proteins. Overexpression experiments have suggested an essential role for Meis factors in limb proximo-distal patterning; however, loss-of-function experiments supporting this notion have not been reported. Meis1 and Meis2 are coexpressed during limb development, first in the lateral plate mesoderm, before limb induction, and then they become restricted to a proximal domain of the growing limb bud. Here, we report that complete double conditional Meis1/2 inactivation in the lateral plate mesoderm leads to limb agenesis. Meis factors cooperate with Tbx factors in this function, extensively co-binding with Tbx to genomic sites and co-regulating enhancers of fgf10, a critical factor in limb initiation. Limbs with three deleted Meis alleles develop a complete PD set of limb skeletal elements, but show proximal-specific skeletal hypoplasia and agenesis of posterior skeletal elements. This failure in posterior skeletal element specification reveals an early role of Meis factors in establishing the limb AP prepattern required for Shh activation at later stages. Our results uncover novel roles for Meis transcription factors in early limb development and identify their involvement in new molecular interaction networks that regulate organogenesis.
Project description:Meis1 and Meis2 are highly similar homeodomain transcription factors that regulate organogenesis through cooperation with Hox proteins. Overexpression experiments have suggested an essential role for Meis factors in limb proximo-distal patterning; however, loss-of-function experiments supporting this notion have not been reported. Meis1 and Meis2 are coexpressed during limb development, first in the lateral plate mesoderm, before limb induction, and then they become restricted to a proximal domain of the growing limb bud. Here, we report that complete double conditional Meis1/2 inactivation in the lateral plate mesoderm leads to limb agenesis. Meis factors cooperate with Tbx factors in this function, extensively co-binding with Tbx to genomic sites and co-regulating enhancers of fgf10, a critical factor in limb initiation. Limbs with three deleted Meis alleles develop a complete PD set of limb skeletal elements, but show proximal-specific skeletal hypoplasia and agenesis of posterior skeletal elements. This failure in posterior skeletal element specification reveals an early role of Meis factors in establishing the limb AP prepattern required for Shh activation at later stages. Our results uncover novel roles for Meis transcription factors in early limb development and identify their involvement in new molecular interaction networks that regulate organogenesis
Project description:While Hox genes encode for similar transcription factors (TFs), they induce different fates across body axes. We sought to understand how Hox TF genomic binding preferences relate to their patterning activities during neuronal differentiation. To generate the required neuronal diversity for locomotor activity, Hox TFs specify spinal motor neuron and interneuron subtypes along the rostro-caudal axis. Our data revelated that Hoxc6 and Hoxc8 of the central group induce limb-innervating fates by binding to the same sites. On the other hand, the posterior group Hox genes assign different positional identities: Hoxc9 (thoracic), Hoxc10 (limb-innervating) and Hox13 (axial elongation termination) by binding to distinct sites with the same primary motif. We find that their genomic binding distributions are explained by differential abilities to bind to previously inaccessible chromatin. Thus, the vertebrate posterior Hox expansion and its associated patterning diversification is the product of their differential abilities to associate with less accessible chromatin.