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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.
The pineal gland is a small endocrine gland in the brain of most vertebrates. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles. The shape of the gland resembles a pine cone, which gives it its name. The pineal gland is located in the epithalamus, near the center of the brain, between the two hemispheres, tucked in a groove where the two halves of the thalamus join. It is one of the neuroendocrine secretory circumventricular organs in which capillaries are mostly permeable to solutes in the blood.
The paraventricular nucleus is a nucleus in the hypothalamus. Anatomically, it is adjacent to the third ventricle and many of its neurons project to the posterior pituitary. These projecting neurons secrete oxytocin and a smaller amount of vasopressin, otherwise the nucleus also secretes corticotropin-releasing hormone (CRH) and thyrotropin-releasing hormone (TRH). CRH and TRH are secreted into the hypophyseal portal system and act on different targets neurons in the anterior pituitary. PVN is thought to mediate many diverse functions through these different hormones, including osmoregulation, appetite, and the response of the body to stress.
Pinealocytes are the main cells contained in the pineal gland, located behind the third ventricle and between the two hemispheres of the brain. The primary function of the pinealocytes is the secretion of the hormone melatonin, important in the regulation of circadian rhythms. In humans, the suprachiasmatic nucleus of the hypothalamus communicates the message of darkness to the pinealocytes, and as a result, controls the day and night cycle. It has been suggested that pinealocytes are derived from photoreceptor cells. Research has also shown the decline in the number of pinealocytes by way of apoptosis as the age of the organism increases. There are two different types of pinealocytes, type I and type II, which have been classified based on certain properties including shape, presence or absence of infolding of the nuclear envelope, and composition of the cytoplasm.
The arcuate nucleus of the hypothalamus is an aggregation of neurons in the mediobasal hypothalamus, adjacent to the third ventricle and the median eminence. The arcuate nucleus includes several important and diverse populations of neurons that help mediate different neuroendocrine and physiological functions, including neuroendocrine neurons, centrally projecting neurons, and astrocytes. The populations of neurons found in the arcuate nucleus are based on the hormones they secrete or interact with and are responsible for hypothalamic function, such as regulating hormones released from the pituitary gland or secreting their own hormones. Neurons in this region are also responsible for integrating information and providing inputs to other nuclei in the hypothalamus or inputs to areas outside this region of the brain. These neurons, generated from the ventral part of the periventricular epithelium during embryonic development, locate dorsally in the hypothalamus, becoming part of the ventromedial hypothalamic region. The function of the arcuate nucleus relies on its diversity of neurons, but its central role is involved in homeostasis. The arcuate nucleus provides many physiological roles involved in feeding, metabolism, fertility, and cardiovascular regulation.
Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the gut, muscles, and heart.
Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins and encoded by the gene Opn4. In the mammalian retina, there are two additional categories of opsins, both involved in the formation of visual images: rhodopsin and photopsin in the rod and cone photoreceptor cells, respectively.
The epithalamus is a posterior (dorsal) segment of the diencephalon. The epithalamus includes the habenular trigone, the stria medullaris, and the pineal gland.
Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the correct structures form in the correct places of the body. For example, Hox genes in insects specify which appendages form on a segment, and Hox genes in vertebrates specify the types and shape of vertebrae that will form. In segmented animals, Hox proteins thus confer segmental or positional identity, but do not form the actual segments themselves.
Otic vesicle, or auditory vesicle, consists of either of the two sac-like invaginations formed and subsequently closed off during embryonic development. It is part of the neural ectoderm, which will develop into the membranous labyrinth of the inner ear. This labyrinth is a continuous epithelium, giving rise to the vestibular system and auditory components of the inner ear. During the earlier stages of embryogenesis, the otic placode invaginates to produce the otic cup. Thereafter, the otic cup closes off, creating the otic vesicle. Once formed, the otic vesicle will reside next to the neural tube medially, and on the lateral side will be paraxial mesoderm. Neural crest cells will migrate rostral and caudal to the placode.
PDX1, also known as insulin promoter factor 1, is a transcription factor in the ParaHox gene cluster. In vertebrates, Pdx1 is necessary for pancreatic development, including β-cell maturation, and duodenal differentiation. In humans this protein is encoded by the PDX1 gene, which was formerly known as IPF1. The gene was originally identified in the clawed frog Xenopus laevis and is present widely across the evolutionary diversity of bilaterian animals, although it has been lost in evolution in arthropods and nematodes. Despite the gene name being Pdx1, there is no Pdx2 gene in most animals; single-copy Pdx1 orthologs have been identified in all mammals. Coelacanth and cartilaginous fish are, so far, the only vertebrates shown to have two Pdx genes, Pdx1 and Pdx2.
POU is a family of eukaryotic transcription factors that have well-conserved homeodomains. The Pou domain is a bipartite DNA binding domain found in these proteins.
Homeobox protein OTX2 is a protein that in humans is encoded by the OTX2 gene.
Nodal homolog is a secretory protein that in humans is encoded by the NODAL gene which is located on chromosome 10q22.1. It belongs to the transforming growth factor beta superfamily. Like many other members of this superfamily it is involved in cell differentiation in early embryogenesis, playing a key role in signal transfer from the primitive node, in the anterior primitive streak, to lateral plate mesoderm (LPM).
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. 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.
The Nodal signaling pathway is a signal transduction pathway important in regional and cellular differentiation during embryonic development.
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.
The dorsal tegmental nucleus (DTN), also known as dorsal tegmental nucleus of Gudden (DTg), is a group of neurons located in the brain stem, which are involved in spatial navigation and orientation.
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.
References
- ↑ "Entrez Gene: BSX brain-specific homeobox".
- ↑ Ferrier, David E. K. (14 April 2016). "Evolution of Homeobox Gene Clusters in Animals: The Giga-Cluster and Primary vs. Secondary Clustering". Frontiers in Ecology and Evolution. 4. doi: 10.3389/fevo.2016.00036 .
- ↑ Cremona, M; Colombo, E; Andreazzoli, M; Cossu, G; Broccoli, V (January 2004). "Bsx, an evolutionary conserved Brain Specific homeoboX gene expressed in the septum, epiphysis, mammillary bodies and arcuate nucleus". Gene Expression Patterns. 4 (1): 47–51. doi:10.1016/S1567-133X(03)00151-0. PMID 14678827.
- ↑ Sakkou, M; Wiedmer, P; Anlag, K; Hamm, A; Seuntjens, E; Ettwiller, L; Tschöp, MH; Treier, M (June 2007). "A role for brain-specific homeobox factor Bsx in the control of hyperphagia and locomotory behavior". Cell Metabolism. 5 (6): 450–63. doi: 10.1016/j.cmet.2007.05.007 . PMID 17550780.
- ↑ D'Autilia, S.; Broccoli, V.; Barsacchi, G.; Andreazzoli, M. (22 March 2010). "Xenopus Bsx links daily cell cycle rhythms and pineal photoreceptor fate". Proceedings of the National Academy of Sciences. 107 (14): 6352–6357. Bibcode:2010PNAS..107.6352D. doi: 10.1073/pnas.1000854107 . PMC 2852004 . PMID 20308548.
- ↑ Schredelseker, Theresa; Driever, Wolfgang (1 July 2018). "Bsx controls pineal complex development". Development. 145 (13): dev163477. doi: 10.1242/dev.163477 . PMID 29945867.
- ↑ Duboc, Véronique; Dufourcq, Pascale; Blader, Patrick; Roussigné, Myriam (23 November 2015). "Asymmetry of the Brain: Development and Implications". Annual Review of Genetics. 49 (1): 647–672. doi:10.1146/annurev-genet-112414-055322. PMID 26442849.