Homeobox protein goosecoid(GSC) is a homeobox protein that is encoded in humans by the GSC gene. Like other homeobox proteins, goosecoid functions as a transcription factor involved in morphogenesis. In Xenopus , GSC is thought to play a crucial role in the phenomenon of the Spemann-Mangold organizer. [5] Through lineage tracing and timelapse microscopy, the effects of GSC on neighboring cell fates could be observed. In an experiment that injected cells with GSC and observed the effects of uninjected cells, GSC recruited neighboring uninjected cells in the dorsal blastopore lip of the Xenopus gastrula to form a twinned dorsal axis, suggesting that the goosecoid protein plays a role in the regulation and migration of cells during gastrulation. [6] [5]
It is not clear how GSC conducts this organizational function. Errors in the formation of goosecoid protein in mice and humans have a range of consequences on the developing embryo typically in regions of neural crest cell derivatives, the hip and shoulder joints, and craniofacial development. Short stature, auditory canal atresia, mandibular hypoplasia, and skeletal abnormalities (SAMS) was thought to be a rare autosomal recessive developmental disorder, but through whole-exome sequencing, it was discovered that SAMS is the result of a mutation of the GSC gene. [7] The data collected from the whole-exome sequencing, as well as the phenotypical presentation of SAMS, indicates that in mammals, the goosecoid protein is involved with the regulation and migration of neural crest cell fates and other mesodermal patterning, notably joints like the shoulders and hips. [8]
The GSC gene defines neural-crest cell-fate specification and contributes to dorsal-ventral patterning. Over activation in Xenopus promotes dorso-anterior migration and dorsalization of mesodermal tissue of the cells along with BMP-4. [9] Conversely, loss-of-functions analysis indirectly prevented head formation in Xenopus [10] and head defects in zebrafish. [11] Although, knock-out studies in mice showed that the GSC gene is not required for gastrulation, knocking out the gene results in there still being a reduction of the base of the cranium. A mutation in the GSC gene in Drosophila is lethal. [12]
GSC gene promotes the formation of Spemann’s Organizer. This organizer prevents BMP-4 from inducing the ectoderm in the future head region of the embryo to become epidermis; it instead allows the future head region to form neural folds, which will eventually turn into the brain and spinal cord. For normal anterior development to occur, Spemann’s organizer cannot express the Xwnt-8 or BMP-4 transcription factors. GSC directly represses the expression of Xwnt-8 while indirectly repressing BMP-4. [13] The inhibition of Xwnt-8 and BMP-4 ensures that normal anterior development, promoted by Spemann’s organizer, can occur.
The expression of GSC occurs twice in development, first during gastrulation and second during organogenesis. [14] GSC is found in high concentrations in the dorsal mesoderm and endoderm during gastrulation. The later expression of GSC is confined to the head region. In the frog Xenopus, cells that express GSC become the pharyngeal endoderm, the head's mesoderm, ventral skeletal tissue of the head, and the notocord. [15]
A mutation in the GSC gene causes short stature, auditory canal atresia, mandibular hypoplasia, and skeletal abnormalities (SAMS). SAMS was previously thought to be an autosomal-recessive disorder but studies with molecular karyotyping and whole-exome sequencing (WES) has shown otherwise. [7]
Mutations in the Gsc gene can lead to specific phenotypes resulting from the second expression of the Gsc gene during organogenesis. Mice knock-out models of the gene express defects in the tongue, nasal cavity, nasal pits, inner ear, and external auditory meatus. [16] Neonate mice born with this mutation die within 24 hours due to complication with breathing and sucking milk, resulting from the craniofacial abnormalities caused by the mutation. Mutations to the Gsc gene in humans can lead to a condition known as SAMS syndrome, characterized by short stature, auditory canal atresia, mandibular hypoplasia, and skeletal abnormalities. [7] [17]
Due to its role as a transcription factor in cell migration during embryonic development, GSC has been looked into as a potential role-player in cancer development and metastasis, since embryonic development and cancer development share similar characteristics. GSC, along with other transcription factors like Twist, FOXC2, and Snail, induce epithelial to mesenchymal transitions by regulating the cell adhesion proteins E-cadherin, α-catenin and γ-catenin expression in epithelial cells. [18] Studies have shown that in highly metastatic ovarian, lung, breast, and other cancer cells, GSC is highly expressed early in the progression of the tumor. [19] Furthermore, high levels of GSC expression in cancer cells correlates with poor survival rates and thus can be used as a prognostic tool. [20] High expression of GSC also correlates with the chemoresistance of the cancer. Therefore, GSC “primes cells for the expression of aggressive phenotypes [19] ” and “may be the most potential biomarker of drug response and poor prognosis. [20] ”
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.
Gastrulation is the stage in the early embryonic development of most animals, during which the blastula, or in mammals the blastocyst, is reorganized into a two-layered or three-layered embryo known as the gastrula. Before gastrulation, the embryo is a continuous epithelial sheet of cells; by the end of gastrulation, the embryo has begun differentiation to establish distinct cell lineages, set up the basic axes of the body, and internalized one or more cell types including the prospective gut.
The primitive node is the organizer for gastrulation in most amniote embryos. In birds, it is known as Hensen's node, and in amphibians, it is known as the Spemann-Mangold organizer. It is induced by the Nieuwkoop center in amphibians, or by the posterior marginal zone in amniotes including birds.
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Chordin is a protein with a prominent role in dorsal–ventral patterning during early embryonic development. In humans it is encoded for by the CHRD gene.
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Growth/differentiation factor 5 is a protein that in humans is encoded by the GDF5 gene.
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Homeobox protein OTX2 is a protein that in humans is encoded by the OTX2 gene.
Homeobox protein GBX-2 is a protein that in humans is encoded by the GBX2 gene.
NK3 homeobox 2 also known as NKX3-2 is a human gene. It is a homolog of bagpipe (bap) in Drosophila and therefore also known as Bapx1. The protein encoded by this gene is a homeodomain containing transcription factor.
In avian gastrulation, Koller's sickle is a local thickening of cells at the posterior edge of the upper layer of the area pellucida called the epiblast. Koller's sickle is crucial for avian development, due to its critical role in inducing the differentiation of various avian body parts. Koller's sickle induces primitive streak and Hensen's node, which are major components of avian gastrulation. Avian gastrulation is a process by which developing cells in an avian embryo move relative to one another in order to form the three germ layers.
The Nodal signaling pathway is a signal transduction pathway important in regional and cellular differentiation during embryonic development.
Edward Michael De Robertis is an American embryologist and Professor at the University of California, Los Angeles. His work has contributed to the finding of conserved molecular processes of embryonic inductions that result in tissue differentiations during animal development. He was elected to the National Academy of Sciences in 2013, worked for the Howard Hughes Medical Institute for 26 years, and holds a Distinguished Professor at the University of California, Los Angeles. In 2009 Pope Benedict XVI appointed De Robertis to a lifetime position in the Pontifical Academy of Sciences, and in 2022 Pope Francis appointed him Councillor of the Academy for four years.
Retinal homeobox protein Rx also known as retina and anterior neural fold homeobox is a protein that in humans is encoded by the RAX gene. The RAX gene is located on chromosome 18 in humans, mice, and rats.
Xbra is a homologue of Brachyury (T) gene for Xenopus. It is a transcription activator involved in vertebrate gastrulation which controls posterior mesoderm patterning and notochord differentiation by activating transcription of genes expressed throughout mesoderm. The effects of Xbra is concentration dependent where concentration gradient controls the development of specific types of mesoderm in Xenopus. Xbra results of the expression of the FGF transcription factor, synthesized by the ventral endoderm. So while ventral mesoderm is characterized by a high concentration of FGF and Xbra, the dorsal mesoderm is characterized by a reunion of two others transcription factors, Siamois and XnR, which activates the synthesis of Goosecoid Transcription Factor. Goosecoid enables the depletion of Xbra. In a nutshell, high concentrations of Xbra induce ventral mesoderm while low concentration stimulates the formation of a back.
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The Spemann-Mangold organizer is a group of cells that are responsible for the induction of the neural tissues during development in amphibian embryos. First described in 1924 by Hans Spemann and Hilde Mangold, the introduction of the organizer provided evidence that the fate of cells can be influenced by factors from other cell populations. This discovery significantly impacted the world of developmental biology and fundamentally changed the understanding of early development.
The dorsal lip of the blastopore is a structure that forms during early embryonic development and is important for its role in organizing the germ layers. The dorsal lip is formed during early gastrulation as folding of tissue along the involuting marginal zone of the blastocoel forms an opening known as the blastopore. It is particularly important for its role in neural induction through the default model, where signaling from the dorsal lip protects a region of the epiblast from becoming epidermis, thus allowing it to develop to its default neural tissue.
A developmental signaling center is defined as a group of cells that release various morphogens which can determine the fates, or destined cell types, of adjacent cells. This process in turn determines what tissues the adjacent cells will form. Throughout the years, various development signaling centers have been discovered.