Scleraxis

SCX
Identifiers
Aliases	SCX, SCXA, SCXB, bHLHa48, LOC642658, scleraxis bHLH transcription factor
External IDs	OMIM: 609067; MGI: 102934; GeneCards: SCX
Gene location (Human) Chr. Chromosome 8 (human) Band 8q24.3 Start 144,266,453 bp End 144,268,481 bp
Gene location (Mouse) Chr. Chromosome 15 (mouse) Band 15 D3|15 35.92 cM Start 76,341,652 bp End 76,343,658 bp
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in thymus quadriceps femoris muscle right lobe of thyroid gland left lobe of thyroid gland Achilles tendon right hemisphere of cerebellum anterior pituitary muscle of thigh gonad ascending aorta Top expressed in digit toe metatarsal bones fifth metatarsal bone interventricular septum plantaris muscle cardiac muscle tissue of left ventricle fourth metatarsal bone extensor digitorum longus muscle finger More reference expression data BioGPS n/a
Gene ontology Molecular function RNA polymerase II cis-regulatory region sequence-specific DNA binding DNA binding sequence-specific DNA binding protein dimerization activity bHLH transcription factor binding E-box binding DNA-binding transcription activator activity, RNA polymerase II-specific protein heterodimerization activity DNA-binding transcription factor activity, RNA polymerase II-specific Cellular component transcription regulator complex nucleus Biological process cellular response to transforming growth factor beta stimulus positive regulation of collagen biosynthetic process cell differentiation regulation of transcription, DNA-templated chondrocyte differentiation regulation of cartilage development positive regulation of gastrulation collagen fibril organization tendon development tendon cell differentiation mesoderm formation cellular response to BMP stimulus negative regulation of apoptotic process Sertoli cell differentiation endochondral ossification transcription by RNA polymerase II BMP signaling pathway transcription, DNA-templated sclerotome development embryonic skeletal system development positive regulation of transcription, DNA-templated multicellular organism development deltoid tuberosity development cellular response to mechanical stimulus positive regulation of gene expression heart valve formation positive regulation of cartilage development heart valve morphogenesis tissue homeostasis positive regulation of cell population proliferation tendon formation skeletal muscle cell differentiation negative regulation of transcription, DNA-templated face morphogenesis positive regulation of transcription by RNA polymerase II Sources:Amigo / QuickGO
Orthologs Databases NCBI: entry; OMA: entry Species Human Mouse Entrez 642658 20289 Ensembl ENSG00000260428 ENSMUSG00000034161 UniProt Q7RTU7 Q64124 RefSeq (mRNA) NM_001008271 NM_001080514 NM_198885 RefSeq (protein) NP_001073983 NP_942588 Location (UCSC) Chr 8: 144.27 – 144.27 Mb Chr 15: 76.34 – 76.34 Mb PubMed search
Wikidata
View/Edit Human View/Edit Mouse

scleraxis homolog A (mouse)
Identifiers
Symbol	SCXA
NCBI gene	333927
HGNC	24312
OMIM	609067
UniProt	Q7RTU7
Other data
Locus	Chr. 8 q24.3
Search for Structures Swiss-model Domains InterPro

scleraxis homolog B (mouse)
Identifiers
Symbol	SCXB
NCBI gene	642658
HGNC	32322
RefSeq	XM_926116
Other data
Locus	Chr. 8 q24.3

The scleraxis protein is a member of the basic helix-loop-helix (bHLH) superfamily of transcription factors. In humans, scleraxis is encoded by the SCX gene.

Function

It is thought that early scleraxis-expressing progenitor cells lead to the eventual formation of tendon tissue and other muscle attachments. Scleraxis is involved in mesoderm formation and is expressed in the syndetome (a collection of embryonic tissue that develops into tendon and blood vessels) of developing somites (primitive segments or compartments of embryos).

Inducing scleraxis expression

The syndetome location within the somite is determined by FGF secreted from the center of the myotome (a collection of embryonic tissue that develops into skeletal muscle)- the FGF then induces the adjacent anterior and posterior sclerotome (a collection of embryonic tissue that develops into the axial skeleton) to adopt a tendon cell fate. This ultimately places future scleraxis-expressing cells between the two tissue types they will ultimately join.

Scleraxis expression will be seen throughout the entire sclerotome (rather than just the sclerotome directly anterior and posterior to the myotome) with an overexpression of FGF8, demonstrating that all sclerotome cells are capable of expressing scleraxis in response to FGF signaling. While the FGF interaction has been shown to be necessary for scleraxis expression, it is still unclear as to whether the FGF signaling pathway directly induces the syndetome to secrete scleraxis, or indirectly through a secondary signaling pathway. Most likely, the syndetomal cells, through careful reading of the FGF concentration (coming from the myotome), can precisely determine their location and begin expressing scleraxis. Much of embryonic development follows this model of inducing specific cell fates through the reading of surrounding signaling molecule concentration gradients.

Background

bHLH transcription factors have been shown to have a wide array of functions in developmental processes. More precisely, they have critical roles in the control of