Neuromere

Neuromeres are morphologically or molecularly defined transient segments of the early developing brain. Rhombomeres are such segments that make up the rhombencephalon or hindbrain. More controversially, some argue that there exist early developmental segments that give rise to structures of the midbrain (mesomeres) and forebrain (prosomeres).

Neuromeres are the segments of the neural tube that establish the embryonic brain during development. They can then be divided up so that each is carrying different and unique genetic traits, expressing different features in development.

Neuromeres were first discovered in the beginning of the 20th century. Although researchers have long since recognized the different signs of differentiation during embryonic development, it was widely thought that neuromeres held no relation to the structure of the nervous system. Swedish neuroembyrologists Bergquist and Kallen clarified the role of neuromeres by conducting several studies showing that neuromeres are important in the development of the nervous system. These experiments consisted of studying the brains of different vertebrates during their development period. During embryonic development, neural crest cells from each neuromere prompt the development of the nerves and arteries, helping to support the development of craniofacial tissues. If gene expression goes wrong, it can have severe effects on the developing embryo, causing abnormalities like craniofacial clefts, also known as cleft palates. The anatomical boundaries of neuromers are determined by the expression of unique genes known as Hox genes in a particular zone. The Hox genes contain the 183-bp homeobox, which encodes a particular portion of the Hox proteins called the homeodomain. The homeodomain can then bind to other portions of DNA to regulate gene expression. These genes determine the basic structure and orientation of an organism after the embryonic segments have formed. The neural crest cells that are found outside of a given neuromere will express the same proteins as the cells that are found inside the neural tube. The genes that are being expressed fall into two categories, extracellular signaling proteins and intracellular transcription factors. The genes are able to perform different tasks at different times depending on the environment that may or not be changing as well as when they are being activated and expressed.

The neural crest was first discovered by Wilhelm His in 1868 when he was studying the embryo of a chick. He first named it Zwischenstrang, which literally translated to mean “intermediate cord.” The name neural crest develops from the neural folds during embryonic development. This is where the neural plate folds in on itself, forming the neural crest. Neural crest cells will eventually become portions of the peripheral nervous system. During development, the neural tube will considered the precursore to the spinal cord and the rest of the nervous system, eventually becoming the Central Nervous System.

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