Homeobox

PRRX1 is part of the paired family of homeobox proteins. PRRX1 functions as a transcription co-activator, enhancing the DNA-binding activity of serum response factor, a protein required for the induction of genes by growth and differentiation factors. PRRX1 also regulates muscle creatine kinase, and therefore has a part in the establishment of diverse mesodermal muscle types. The protein binds to an A/T-rich element in the muscle creatine enhancer. Among the diseases associated with PRRX1 are agnathia-otocephaly complex, and pleomorphic liposarcoma.

NK3 Homeobox1 (NKX3-1) is a homeobox-containing transcription factor, which binds preferentially the consensus sequence 5'-TAAGT[AG]-3' and may act as a transcriptional repressor. The NKX3-1 transcription factor functions as a negative regulator of epithelial cell growth in prostate tissue. NKX3-1 has an imperative role in normal prostate development, regulating proliferation of glandular epithelium and in the formation of ducts in prostate. In addition, NKX3-1 functions as a tumor suppressor controlling prostate carcinogenesis, as shown by its ability to inhibit proliferation and invasion activities of PC-3 prostate cancer cells. Abnormal expression of NKX3-1 is linked with prostate tumor progression.

DLX3 belongs to the Distal-less (Dlx) family of genes which includes at least 6 different members. DLX3 plays a regulatory role in the development of the ventral forebrain and also in craniofacial patterning and morphogenesis. Mutation in DLX3 is correlated with Trichodentoosseous syndrome which is an autosomal dominant condition. DLX3 is located in a tail-to-tail configuration with another member of the gene family on the long arm of chromosome 17.

Homeobox C11 (HOXC11) is a member of the Abd-B homeobox family. The homeobox genes encode well conservedfamily of transcription factors that play a vital role in morphogenesis in all multicellular organisms. HOXC11is one of numerous homeobox HOXC genes placed in a cluster on chromosome 12. HOXC11 attaches to a promoterelement of the lactase-phlorizin hydrolase. HOXC11 also takes part in early intestinal development. An alternativelyspliced variant encoding a shorter isoform has been defined however, its full-length nature has not been determined.

HOXB13 is a transcription factor and a member of the homeobox gene family which are extremely conserved in vertebrates and vital for vertebrate embryonic development. HOXB13 is involved in fetal skin development and cutaneous regeneration. In mice, a similar gene displayed temporal and spatial colinearity in the main body axis of the embryo, however it was not expressed in the secondary axes, implying that it has a roles in body patterning along the axis.

Homeobox A9 (HOXA9) is a member of the Abd-B homeobox family. The HOXA9 protein is a transcription factor with a key role in both haemopoiesis and leukaemia. High levels of HOXA9 expression in haemopoietic cells is a distinctive feature of acute myeloid leukaemia (AML), and may be sufficient to cause this disease. HOXA9 overexpression noticeably expands hematopoietic stem cells. The HOXA9 gene is part of the A cluster on chromosome 7 and encodes a DNA-binding transcription factor which regulates gene expression, morphogenesis, and differentiation. HOXA9 is a sequence-specific transcription factor which is part of a developmental regulatory system, which provides cells with specific positional identities on the anterior-posterior axis. HOXA9 is essential for induction of E-selectin and VCAM-1, on the endothelial cells surface at sites of inflammation.

Homeodomain-only protein (HOPX) functions via its interaction with SRF, thus modulating the expression of SRF-dependent cardiac-specific genes and cardiac development. HOPX inhibits SRF-dependent transcription either by hindering SRF binding to DNA or by engaging histone deacetylase (HDAC) proteins which prevent transcription by SRF. HOPX is a homeodomain protein which lacks certain conserved residues required for DNA binding. HOPX overexpression causes cardiac hypertrophy.

The homeobox protein family of transcription factors has many members that take part in developmental processes such as HHEX. HHEX is known to interact with Promyelocytic leukemia protein and expression in specific hematopoietic lines indicates that this protein is involved in hematopoietic differentiation.

Homeobox protein MOX-2 (MEOX2) is a part of a family of nonclustered, diverged homeobox genes which are expressed in overlapping patterns in the paraxial mesoderm and its derivatives. MEOX2 participates in the regulation of vertebrate limb myogenesis. MEOX2 also takes part in mesoderm induction and its earliest regional specification, somitogenesis, myogenic and sclerotomal differentiation. Mutations in the related mouse MEOX2 are related with craniofacial and/or skeletal abnormalities, in addition to neurovascular dysfunction observed in Alzheimer's disease.