Scleraxis
Encyclopedia
The scleraxis protein
is a member of the basic-helix-loop-helix
(bHLH) superfamily of transcription factor
s. Currently two genes ( and respectively) have been identified to code for identical scleraxis proteins.
s lead to the eventual formation of tendon tissue and other muscle attachments. Scleraxis is involved in mesoderm
formation and is expressed in the syndetomal (embryonic tissues that develop into tendon and blood vessels) compartment of developing somite
s (primitive segments or compartments of embryos).
processes. More precisely, they have critical roles in the control of cellular differentiation
, proliferation
and regulation of oncogenesis. To date, 242 eukaryotic
proteins belonging to the HLH superfamily have been reported. They have varied expression patterns in all eukaryotes from yeast to humans.
Structurally, bHLH proteins are characterised by a “highly conserved domain containing a stretch of basic amino acid
s adjacent to two amphipathic α-helices
separated by a loop”.
These helices have important functional properties, forming part of the DNA binding and transcription activating domains. With respect to scleraxis, the bHLH region spans amino acid residues 78 to 131. A proline rich region is also predicted to lie between residues 161-170. A stretch of basic residues, which aids in DNA binding, is found closer to the N terminal end of scleraxis.
HLH proteins that lack this basic domain have been shown to negatively regulate the activities of bHLH proteins and are called inhibitors of differentiation (Id). Basic HLH proteins function normally as dimers and bind to a specific hexanucleotide DNA sequence (CAANTG) known as an E-box
thus switching on the expression of various genes involved in cellular development and survival.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
is a member of the basic-helix-loop-helix
Basic-helix-loop-helix
A basic helix-loop-helix is a protein structural motif that characterizes a family of transcription factors.- Structure :The motif is characterized by two α-helices connected by a loop. In general, transcription factors including this domain are dimeric, each with one helix containing basic amino...
(bHLH) superfamily of transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
s. Currently two genes ( and respectively) have been identified to code for identical scleraxis proteins.
Function
It is thought that early scleraxis expressing progenitor cellProgenitor cell
A progenitor cell is a biological cell that, like a stem cell, has a tendency to differentiate into a specific type of cell, but is already more specific than a stem cell and is pushed to differentiate into its "target" cell...
s lead to the eventual formation of tendon tissue and other muscle attachments. Scleraxis is involved in mesoderm
Mesoderm
In all bilaterian animals, the mesoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and endoderm , with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme , mesothelium, non-epithelial blood corpuscles and...
formation and is expressed in the syndetomal (embryonic tissues that develop into tendon and blood vessels) compartment of developing somite
Somite
A somite is a division of the body of an animal. In vertebrates this is mainly discernible in the embryo stage; in arthropods it is a characteristic of a hypothetical ancestor.- In vertebrates :...
s (primitive segments or compartments of embryos).
Background
bHLH transcription factors have been shown to have a wide array of functions in developmentalDevelopmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
processes. More precisely, they have critical roles in the control of cellular differentiation
Cellular differentiation
In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...
, proliferation
Cell growth
The term cell growth is used in the contexts of cell development and cell division . When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two "daughter cells"...
and regulation of oncogenesis. To date, 242 eukaryotic
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
proteins belonging to the HLH superfamily have been reported. They have varied expression patterns in all eukaryotes from yeast to humans.
Structurally, bHLH proteins are characterised by a “highly conserved domain containing a stretch of basic amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s adjacent to two amphipathic α-helices
Alpha helix
A common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...
separated by a loop”.
These helices have important functional properties, forming part of the DNA binding and transcription activating domains. With respect to scleraxis, the bHLH region spans amino acid residues 78 to 131. A proline rich region is also predicted to lie between residues 161-170. A stretch of basic residues, which aids in DNA binding, is found closer to the N terminal end of scleraxis.
HLH proteins that lack this basic domain have been shown to negatively regulate the activities of bHLH proteins and are called inhibitors of differentiation (Id). Basic HLH proteins function normally as dimers and bind to a specific hexanucleotide DNA sequence (CAANTG) known as an E-box
E-box
An E-box is a DNA sequence which usually lies upstream of a gene in a promoter region. It is a transcription factor binding site where the specific sequence of DNA, CANNTG, is recognized by proteins that can bind to it to help initiate its transcription. Once transcription factors bind to...
thus switching on the expression of various genes involved in cellular development and survival.