LIM homeobox 1 is a protein that in humans is encoded by the LHX1 gene. [5] This gene encodes a member of a large protein family which contains the LIM domain, a unique cysteine-rich zinc-binding domain. The encoded protein is a transcription factor important for control of differentiation and development of neural and lymphoid cells. It is also key in development of renal and urogenital systems and is required for normal organogenesis. [6] A similar protein in mice is an essential regulator of the vertebrate head organizer. [5]
The Lim gene family is a subfamily of homeobox genes. [7] The homeobox genes are essential in organizing the body plan of an organism and all contain the same conserved homeodomain of amino acids. [8] Evidence that Lim-1 is essential to a developing organism is its conservation throughout evolution and presence in a variety of organisms. [7] The Lim-1 gene encodes a transcription factor which binds to the DNA of specific genes and functions to produce the needed gene product for development of the organism. [9] Lim-1 is important during early molecular development and is required in both primitive streak-derived tissue and visceral endoderm of the early embryo for development of a head. [10] Studies done using mutant organisms without the Lim gene results in organisms that develop no head structure at all support the essential role of the Lim-1 gene in formation of the head. [11] This gene has also been shown to play a crucial role in the formation of the female reproductive tract. [9] The gene is expressed in the developing Müllerian duct of females, and when the gene is knocked out no reproductive tract forms. [9] Recent studies have shown that Lim-1 mutations may be one cause of the Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome. [12] MRKH is characterized by defective development, or absence, of the uterus and upper part of the vagina in women with normal ovaries and karyotype. [12]
Lim-1’s expression is controlled in part by the sonic hedgehog-Gli signaling pathway. [6] Recent studies in mice have shown that Lim-1 silencing halts tumor growth and impairs tumor cell movement via inhibition of protein expression involved in metastatic spread. [6] Therefore, in tumor cells Lim-1 acts as an oncogene. [6] Thus, targeting Lim-1 can be a potential cancer therapy. In addition, Lim-1 is important in rodent renal development. [13] Lim-1 deficiency results in development of multicystic kidney, whereas, its expression can contribute to pathogenesis of nephroblastomas. [13] Also, Lim-1 plays a role in embryonic retinal development. [14] Lim-1 expression affects differentiation and maintenance of horizontal cells located in the retinal, thus, it could serve as a marker in studies of horizontal cell specification. [14]
Lim-1 (Lhx1) functions as a transcription factor necessary for regulating the production of coupling factors required for proper communication between the neurons located in the part of the brain responsible for regulation of circadian rhythms called the suprachiasmatic nucleus (SCN). [15] In mouse studies where Lim-1 transcription was restricted at some point during development in utero, the individual units within the subject’s molecular clock functioned properly but were unable to work together. [15] Communication of these units is required to match their release of clock proteins which begin a transcription cascade of many other proteins that produce functional responses in tissues. [15] The cyclic pattern of these responses is due to the feedback of the clock proteins and consequent changes to this transcription cascade. [15] Reduced Lim-1 expression leads to inadequate levels of proteins such as Vasoactive Intestinal Polypeptide (VIP) that work to produce the neuron coordination required for a regulated circadian rhythm. [15] The lack of such coupling factors causes the circadian clock to not function properly because the units within the SCN cannot match their release of clock proteins, and therefore their transcriptional cascades of proteins that cause changes in arousal do not align. [15]
A homeobox is a DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. Mutations in a homeobox may change large-scale anatomical features of the full-grown organism.
Neuronal PAS domain protein 2 (NPAS2) also known as member of PAS protein 4 (MOP4) is a transcription factor protein that in humans is encoded by the NPAS2 gene. NPAS2 is paralogous to CLOCK, and both are key proteins involved in the maintenance of circadian rhythms in mammals. In the brain, NPAS2 functions as a generator and maintainer of mammalian circadian rhythms. More specifically, NPAS2 is an activator of transcription and translation of core clock and clock-controlled genes through its role in a negative feedback loop in the suprachiasmatic nucleus (SCN), the brain region responsible for the control of circadian rhythms.
Aryl hydrocarbon receptor nuclear translocator-like 2, also known as Arntl2, Mop9, Bmal2, or Clif, is a gene.
Period circadian protein homolog 1 is a protein in humans that is encoded by the PER1 gene.
Pre-B-cell leukemia transcription factor 1 is a protein that in humans is encoded by the PBX1 gene. The homologous protein in Drosophila is known as extradenticle, and causes changes in embryonic development.
Homeobox protein Nkx-3.1, also known as NKX3-1, NKX3, BAPX2, NKX3A and NKX3.1 is a protein that in humans is encoded by the NKX3-1 gene located on chromosome 8p. NKX3-1 is a prostatic tumor suppressor gene.
Paired-like homeodomain transcription factor 2 also known as pituitary homeobox 2 is a protein that in humans is encoded by the PITX2 gene.
Homeobox protein MSX-2 is a protein that in humans is encoded by the MSX2 gene.
Homeobox protein Hox-A1 is a protein that in humans is encoded by the HOXA1 gene.
Hematopoietically-expressed homeobox protein HHEX is a protein that in humans is encoded by the HHEX gene and also known as Proline Rich Homeodomain protein PRH.
LIM/homeobox protein Lhx3 is a protein that in humans is encoded by the LHX3 gene.
Homeobox protein Hox-B4 is a protein that in humans is encoded by the HOXB4 gene.
T-cell leukemia homeobox protein 1 is a protein that in humans is encoded by the TLX1 gene, which was initially named HOX11.
Homeobox protein OTX2 is a protein that in humans is encoded by the OTX2 gene.
Homeobox protein Hox-D4 is a protein that in humans is encoded by the HOXD4 gene.
Paired related homeobox 1 is a protein that in humans is encoded by the PRRX1 gene.
Homeobox protein SIX5 is a protein that in humans is encoded by the SIX5 gene.
LIM homeobox transcription factor 1, alpha, also known as LMX1A, is a protein which in humans is encoded by the LMX1A gene.
Lim-1 is a homeobox transcription factor. This transcription factor is found in adults in the cerebellum, kidneys, and cerebrum, but plays a larger role in development of the fetal head and the female reproductive tract during gestation. During development it is found in the anterior visceral endoderm, is in tissues formed by the primitive streak, and is required in both tissues for head formation. Lim1 is a member of the LIM homeobox gene and encodes a 406 amino acid protein.
PBX/Knotted 1 Homeobox 2 (PKNOX2) protein belongs to the three amino acid loop extension (TALE) class of homeodomain proteins, and is encoded by PKNOX2 gene in humans. The protein regulates the transcription of other genes and affects anatomical development.
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