Abstract
The bone morphogenetic protein (BMP) signaling pathway regulates multiple steps of hematopoiesis, mediated through receptor-regulated Smads, including Smad1 and Smad5. Here, we use loss-of-function approaches in zebrafish to compare the roles of Smad1 and Smad5 during embryonic hematopoiesis. We show that knockdown of Smad1 or Smad5 generates distinct and even opposite hematopoietic phenotypes. Embryos depleted for Smad1 have an increased number of primitive erythrocytes, but fail to produce mature embryonic macrophages. In contrast, Smad5-depleted embryos are defective in primitive erythropoiesis, yet have normal numbers of macrophages. Loss of either Smad1 or Smad5 causes a failure in the generation of definitive hematopoietic progenitors. To investigate the mechanism behind these phenotypes, we used rescue experiments and found that Smad5 is unable to rescue the Smad1 loss-of-function phenotype, indicating that the 2 highly related proteins have inherently distinct activities. Microarray experiments revealed that the 2 proteins redundantly regulate the key initiators of the hemato-vascular program, including scl, lmo2, and gfi1. However, each also regulates a remarkably distinct genetic program, with Smad5 uniquely regulating the BMP signaling pathway itself. Our results suggest that specificity of BMP signaling output, with respect to hematopoiesis, can be explained by differential functions of Smad1 and Smad5.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Basic Helix-Loop-Helix Transcription Factors / biosynthesis
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Basic Helix-Loop-Helix Transcription Factors / genetics
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Bone Morphogenetic Proteins / genetics
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Bone Morphogenetic Proteins / metabolism
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DNA-Binding Proteins / biosynthesis
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DNA-Binding Proteins / genetics
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Embryo, Nonmammalian / cytology
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Embryo, Nonmammalian / metabolism
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Erythrocytes / cytology
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Erythrocytes / metabolism
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Gene Expression Profiling
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Gene Expression Regulation, Developmental / physiology*
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Hematopoiesis / physiology*
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Hematopoietic Stem Cells / cytology
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Hematopoietic Stem Cells / metabolism*
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LIM Domain Proteins
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Macrophages / cytology
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Macrophages / metabolism
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Metalloproteins / biosynthesis
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Metalloproteins / genetics
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Oligonucleotide Array Sequence Analysis
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Proto-Oncogene Proteins / biosynthesis
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Proto-Oncogene Proteins / genetics
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Signal Transduction / physiology
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Smad1 Protein / genetics
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Smad1 Protein / metabolism*
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Smad5 Protein / genetics
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Smad5 Protein / metabolism*
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T-Cell Acute Lymphocytic Leukemia Protein 1
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Transcription Factors
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Zebrafish / embryology*
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Zebrafish / genetics
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Zebrafish Proteins / biosynthesis
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Zebrafish Proteins / genetics
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Zebrafish Proteins / metabolism*
Substances
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Basic Helix-Loop-Helix Transcription Factors
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Bone Morphogenetic Proteins
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DNA-Binding Proteins
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LIM Domain Proteins
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Metalloproteins
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Proto-Oncogene Proteins
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Smad1 Protein
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Smad5 Protein
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T-Cell Acute Lymphocytic Leukemia Protein 1
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Transcription Factors
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Zebrafish Proteins
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gfi1ab protein, zebrafish
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lmo2 protein, zebrafish
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smad5 protein, zebrafish
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tal1 protein, zebrafish