Abstract
The homeodomain transcription factor Nkx2.2 is essential for pancreatic development and islet cell type differentiation. We have identified Tm4sf4, an L6 domain tetraspanin family member, as a transcriptional target of Nkx2.2 that is greatly upregulated during pancreas development in Nkx2.2(-/-) mice. Tetraspanins and L6 domain proteins recruit other membrane receptors to form active signaling centers that coordinate processes such as cell adhesion, migration and differentiation. In this study, we determined that Tm4sf4 is localized to the ductal epithelial compartment and is prominent in the Ngn3(+) islet progenitor cells. We also established that pancreatic tm4sf4 expression and regulation by Nkx2.2 is conserved during zebrafish development. Loss-of-function studies in zebrafish revealed that tm4sf4 inhibits α and β cell specification, but is necessary for ε cell fates. Thus, Tm4sf4 functional output opposes that of Nkx2.2. Further investigation of how Tm4sf4 functions at the cellular level in vitro showed that Tm4sf4 inhibits Rho-activated cell migration and actin organization in a ROCK-independent fashion. We propose that the primary role of Nkx2.2 is to inhibit Tm4sf4 in endocrine progenitor cells, allowing for delamination, migration and/or appropriate cell fate decisions. Identification of a role for Tm4sf4 during endocrine differentiation provides insight into islet progenitor cell behaviors and potential targetable regenerative mechanisms.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Amino Acid Sequence
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Animals
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Basic Helix-Loop-Helix Transcription Factors / genetics
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Basic Helix-Loop-Helix Transcription Factors / metabolism
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Cell Differentiation / physiology*
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Cell Line
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Cell Movement / physiology*
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Gene Expression Regulation, Developmental*
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Ghrelin / genetics
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Ghrelin / metabolism
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Homeobox Protein Nkx-2.2
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Homeodomain Proteins / genetics
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Homeodomain Proteins / metabolism*
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Humans
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Islets of Langerhans / cytology
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Islets of Langerhans / embryology*
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Islets of Langerhans / growth & development*
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Islets of Langerhans / metabolism
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Membrane Glycoproteins / genetics
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Membrane Glycoproteins / metabolism*
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Membrane Proteins / genetics
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Membrane Proteins / metabolism*
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Mice
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Mice, Knockout
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Molecular Sequence Data
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Nerve Tissue Proteins / genetics
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Nerve Tissue Proteins / metabolism
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Nuclear Proteins
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Sequence Alignment
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Stem Cells / cytology
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Stem Cells / physiology
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Transcription Factors / genetics
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Transcription Factors / metabolism*
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Zebrafish / anatomy & histology
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Zebrafish / embryology
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Zebrafish / growth & development
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Zebrafish / metabolism
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Zebrafish Proteins / genetics
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Zebrafish Proteins / metabolism*
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rho GTP-Binding Proteins / genetics
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rho GTP-Binding Proteins / metabolism
Substances
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Basic Helix-Loop-Helix Transcription Factors
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Ghrelin
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Homeobox Protein Nkx-2.2
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Homeodomain Proteins
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Membrane Glycoproteins
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Membrane Proteins
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NKX2-2 protein, human
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Nerve Tissue Proteins
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Neurog3 protein, mouse
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Nkx2-2 protein, mouse
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Nuclear Proteins
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Tm4sf4 protein, mouse
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Tm4sf4 protein, zebrafish
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Transcription Factors
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Zebrafish Proteins
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nkx2.2b protein, zebrafish
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rho GTP-Binding Proteins