Smad1/Smad5 signaling in limb ectoderm functions redundantly and is required for interdigital programmed cell death.

School of Life Sciences, The Chinese University of Hong Kong, Hong Kong, PR China.
Developmental Biology (Impact Factor: 3.64). 03/2012; 363(1):247-57. DOI: 10.1016/j.ydbio.2011.12.037
Source: PubMed

ABSTRACT Bone morphogenetic proteins (BMPs) are secreted signals that regulate apical ectodermal ridge (AER) functions and interdigital programmed cell death (PCD) of developing limb. However the identities of the intracellular mediators of these signals are unknown. To investigate the role of Smad proteins in BMP-regulated AER functions in limb development, we inactivated Smad1 and Smad5 selectively in AER and ventral ectoderm of developing limb, using Smad1 or/and Smad5 floxed alleles and an En1(Cre/+) knock-in allele. Single inactivation of either Smad1 or Smad5 did not result in limb abnormalities. However, the Smad1/Smad5 double mutants exhibited syndactyly due to a reduction in interdigital PCD and an increase in interdigital cell proliferation. Cell tracing experiments in the Smad1/Smad5 double mutants showed that ventral ectoderm became thicker and the descendents of ventral En1(Cre/+) expressing ectodermal cells were located at dorsal interdigital regions. At the molecular level, Fgf8 expression was prolonged in the interdigital ectoderm of embryonic day (E) 13 Smad1/Smad5 double mutants, suggesting that the ectopic Fgf8 expression may serve as a survival signal for interdigital epithelial and mesenchymal cells. Our result suggests that Smad1 and Smad5 are required and function redundantly as intracellular mediators for BMP signaling in the AER and ventral ectoderm. Smad1/Smad5 signaling in the AER and ventral ectoderm regulates interdigital tissue regression of developing limb. Our mutants with defects in interdigital PCD could also serve as a valuable model for investigation of PCD regulation machinery.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The analysis of vertebrate limb bud development provides insight of general relevance into the signaling networks that underlie the controlled proliferative expansion of large populations of mesenchymal progenitors, cell fate determination and initiation of differentiation. In particular, extensive genetic analysis of mouse and experimental manipulation of chicken limb bud development has revealed the self-regulatory feedback signaling systems that interlink the main morphoregulatory signaling pathways including BMPs and their antagonists. It this review, we showcase the key role of BMPs and their antagonists during limb bud development. This review provides an understanding of the key morphoregulatory interactions that underlie the highly dynamic changes in BMP activity and signal transduction as limb bud development progresses from initiation and setting-up the signaling centres to determination and formation of the chondrogenic primordia for the limb skeletal elements.
    Seminars in Cell and Developmental Biology 04/2014; · 6.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: BMP signaling is pivotal for normal limb bud development in vertebrate embryos and genetic analysis of receptors and ligands in the mouse revealed their requirement in both mesenchymal and ectodermal limb bud compartments. In this study, we genetically assessed the potential essential functions of SMAD4, a mediator of canonical BMP/TGFß signal transduction, in the mouse limb bud ectoderm. Msx2-Cre was used to conditionally inactivate Smad4 in the ectoderm of fore- and hindlimb buds. In hindlimb buds, the Smad4 inactivation disrupts the establishment and signaling by the apical ectodermal ridge (AER) from early limb bud stages onwards, which results in severe hypoplasia and/or aplasia of zeugo- and autopodal skeletal elements. In contrast, the developmentally later inactivation of Smad4 in forelimb buds does not alter AER formation and signaling, but prolongs epithelial-mesenchymal feedback signaling in advanced limb buds. The late termination of SHH and AER-FGF signaling delays distal progression of digit ray formation and inhibits interdigit apoptosis. In summary, our genetic analysis reveals the temporally and functionally distinct dual requirement of ectodermal Smad4 during initiation and termination of AER signaling. © 2013 Wiley Periodicals, Inc.
    genesis 07/2013; · 2.04 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Interdigital cell death is a physiological regression process responsible for sculpturing the digits in the embryonic vertebrate limb. Changes in the intensity of this degenerative process account for the different patterns of interdigital webbing among vertebrate species. Here, we show that Reelin is present in the extracellular matrix of the interdigital mesoderm of chick and mouse embryos during the developmental stages of digit formation. Reelin is a large extracellular glycoprotein which has important functions in the developing nervous system, including neuronal survival; however, the significance of Reelin in other systems has received very little attention. We show that reelin expression becomes intensely downregulated in both the chick and mouse interdigits preceding the establishment of the areas of interdigital cell death. Furthermore, fibroblast growth factors, which are cell survival signals for the interdigital mesoderm, intensely upregulated reelin expression, while BMPs, which are proapototic signals, downregulate its expression in the interdigit. Gene silencing experiments of reelin gene or its intracellular effector Dab-1 confirmed the implication of Reelin signaling as a survival factor for the limb undifferentiated mesoderm. We found that Reelin activates canonical survival pathways in the limb mesoderm involving protein kinase B and focal adhesion kinase. Our findings support that Reelin plays a role in interdigital cell death, and suggests that anoikis (apoptosis secondary to loss of cell adhesion) may be involved in this process.
    Cell Death & Disease 09/2013; 4:e800. · 5.18 Impact Factor

Full-text (2 Sources)

Available from
Aug 7, 2014