Biomedical subjects

K L Ligon

Publications and source records attributed to K L Ligon.

4 recordsLinked to original sources

PubMed1996

Cooperative transcriptional activation by the neurogenic basic helix-loop-helix protein MASH1 and members of the myocyte enhancer factor-2 (MEF2) family.

Establishment of skeletal muscle and neural cell types is controlled by families of myogenic and neurogenic basic helix-loop-helix (bHLH) proteins, respectively. Myogenic bHLH proteins have been shown to activate skeletal muscle transcription in collaboration with members of the myocyte enhancer factor-2 (MEF2) family of MCM1-agamous-deficiens-serum response factor (MADS)-box transcription factors, which are expressed in differentiated myocytes and neurons. Here, we show that the neurogenic bHLH protein MASH1 interacts with members of the MEF2 family and that this interaction, mediated by the DNA binding and dimerization domains of these factors, results in synergistic activation of transcription through either the MASH1 or the MEF2 DNA binding site. Consistent with their involvement in activation of neuronal gene expression, members of the MEF2 family are expressed in P19 embryonal carcinoma cells that have been induced to form neurons following treatment with retinoic acid. These results suggest that members of the MEF2 family perform similar roles in synergistic activation of transcription in myogenic and neurogenic lineages by serving as cofactors for cell type-specific bHLH proteins.

Animals↗

PubMed1995

Paraxis: a basic helix-loop-helix protein expressed in paraxial mesoderm and developing somites.

During vertebrate embryogenesis, cells from the paraxial mesoderm coalesce in a rostral-to-caudal progression to form the somites. Subsequent compartmentalization of the somites yields the sclerotome, myotome, and dermatome, which give rise to the axial skeleton, axial musculature, and dermis, respectively. Recently, we cloned a novel basic helix-loop-helix (bHLH) protein, called scleraxis, which is expressed in the sclerotome, in mesenchymal precursors of bone and cartilage, and in connective tissues. Here we report the cloning of a bHLH protein, called paraxis, which is nearly identical to scleraxis within the bHLH region but diverges in its amino and carboxyl termini. During mouse embryogenesis, paraxis transcripts are first detected at about Day 7.5 postcoitum within primitive mesoderm lying posterior to the head and heart primordia. Subsequently, paraxis expression progresses caudally through the paraxial mesoderm, immediately preceding somite formation. Paraxis is expressed at high levels in newly formed somites before the first detectable expression of the myogenic bHLH genes, and as the somite becomes compartmentalized, paraxis becomes downregulated in the myotome. Paraxis and scleraxis are coexpressed in the sclerotome, but paraxis expression declines soon after sclerotome formation, whereas scleroaxis expression increases in the sclerotome and its derivatives. The sequential expression of paraxis and scleraxis in the paraxial mesoderm and somites suggests that these bHLH proteins may comprise part of a regulatory pathway involved in patterning of the paraxial mesoderm and in the establishment of somitic cell lineages.

Amino Acid Sequence↗

PubMed1995

Scleraxis: a basic helix-loop-helix protein that prefigures skeletal formation during mouse embryogenesis.

Members of the basic helix-loop-helix (bHLH) family of transcription factors have been shown to regulate growth and differentiation of numerous cell types. Cell-type-specific bHLH proteins typically form heterodimers with ubiquitous bHLH proteins, such as E12, and bind a DNA consensus sequence known as an E-box. We used the yeast two-hybrid system to screen mouse embryo cDNA libraries for cDNAs encoding novel cell-type-specific bHLH proteins that dimerize with E12. One of the cDNAs isolated encoded a novel bHLH protein, called scleraxis. During mouse embryogenesis, scleraxis transcripts were first detected between day 9.5 and 10.5 post coitum (p.c.) in the sclerotome of the somites and in mesenchymal cells in the body wall and limb buds. Subsequently, scleraxis was expressed at high levels within mesenchymal precursors of the axial and appendicular skeleton and in cranial mesenchyme in advance of chondrogenesis; its expression pattern in these cell types foreshadowed the developing skeleton. Prior to formation of the embryonic cartilaginous skeleton, scleraxis expression declined to low levels. As development proceeded, high levels of scleraxis expression became restricted to regions where cartilage and connective tissue formation take place. Scleraxis bound the E-box consensus sequence as a heterodimer with E12 and activated transcription of a reporter gene linked to its DNA-binding site. The expression pattern, DNA-binding properties and transcriptional activity of scleraxis suggest that it is a regulator of gene expression within mesenchymal cell lineages that give rise to cartilage and connective tissue.

Amino Acid Sequence↗

PubMed1994

Smooth muscle myosin heavy chain exclusively marks the smooth muscle lineage during mouse embryogenesis.

We cloned a portion of the mouse smooth muscle myosin heavy chain (SM-MHC) cDNA and analyzed its mRNA expression in adult tissues, several cell lines, and developing mouse embryos to determine the suitability of the SM-MHC promoter as a tool for identifying smooth muscle-specific transcription factors and to define the spatial and temporal pattern of smooth muscle differentiation during mouse development. RNase protection assays showed SM-MHC mRNA in adult aorta, intestine, lung, stomach, and uterus, with little or no signal in brain, heart, kidney, liver, skeletal muscle, spleen, and testes. From an analysis of 14 different cell lines, including endothelial cells, fibroblasts, and rhabdomyosarcomas, we failed to detect any SM-MHC mRNA; all of the cell lines induced to differentiate also showed no detectable SM-MHC. In situ hybridization of staged mouse embryos first revealed SM-MHC transcripts in the early developing aorta at 10.5 days post coitum (dpc). No hybridization signal was demonstrated beyond the aorta and its arches until 12.5 to 13.5 dpc, when SM-MHC mRNA appeared in smooth muscle cells (SMCs) of the developing gut and lungs as well as peripheral blood vessels. By 17.5 dpc, SM-MHC transcripts had accumulated in esophagus, bladder, and ureters. Except for blood vessels, no SM-MHC transcripts were ever observed in developing brain, heart, or skeletal muscle. These results indicate that smooth muscle myogenesis begins by 10.5 days of embryonic development in the mouse and establish SM-MHC as a highly specific marker for the SMC lineage. The SM-MHC promoter should therefore serve as a useful model for defining the mechanisms that govern SMC transcription during development and disease.

Amino Acid Sequence↗