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The location of NORs and the nucleolar cycle in human cells. Nucleolus organizer regions (NORs) are chromosomal regions crucial for the formation of the nucleolus.In humans, the NORs are located on the short arms of the acrocentric chromosomes 13, 14, 15, 21 and 22, the genes RNR1, RNR2, RNR3, RNR4, and RNR5 respectively. [1]
A classic example of a syncytium is the formation of skeletal muscle.Large skeletal muscle fibers form by the fusion of thousands of individual muscle cells. The multinucleated arrangement is important in pathologic states such as myopathy, where focal necrosis (death) of a portion of a skeletal muscle fiber does not result in necrosis of the adjacent sections of that same skeletal muscle ...
Cell Biology in "The Biology Project" of University of Arizona. Centre of the Cell online; The Image & Video Library of The American Society for Cell Biology Archived 2011-06-10 at the Wayback Machine, a collection of peer-reviewed still images, video clips and digital books that illustrate the structure, function and biology of the cell.
Wnt signaling was first identified for its role in carcinogenesis, then for its function in embryonic development. The embryonic processes it controls include body axis patterning, cell fate specification, cell proliferation and cell migration. These processes are necessary for proper formation of important tissues including bone, heart and muscle.
In 1903, Nikolai K. Koltsov proposed that the shape of cells was determined by a network of tubules that he termed the cytoskeleton. The concept of a protein mosaic that dynamically coordinated cytoplasmic biochemistry was proposed by Rudolph Peters in 1929 [12] while the term (cytosquelette, in French) was first introduced by French embryologist Paul Wintrebert in 1931.
The Hox transcription factor family, for example, is important for proper body pattern formation in organisms as diverse as fruit flies to humans. [ 24 ] [ 25 ] Another example is the transcription factor encoded by the sex-determining region Y (SRY) gene, which plays a major role in determining sex in humans.
Furthermore, multinucleate cells are produced from specialized cell cycles in which nuclear division occurs without cytokinesis, thus leading to large coenocytes or plasmodia. In filamentous fungi , multinucleate cells may extend over hundreds of meters so that different regions of a single cell experience dramatically different microenvironments.
Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (the brain and the spinal cord) and in the peripheral nervous system that do not produce electrical impulses. The neuroglia make up more than one half the volume of neural tissue in the human body. [1]