The sarcoplasmic reticulum Ca2+-ATPase (SERCA) isoforms are normally expressed in coordination with the corresponding myosin heavy chain (MyHC) isoforms in the fibers of skeletal muscle but this coordination is often disrupted in pathological conditions. In the streptozotocin-induced diabetes of rats (stz-rats), the soleus muscle showed peripheral neuropathy and the SERCA2a level decreased in type I (slow-oxidative) fibers compared to the control muscles, whereas the expression of the corresponding slow MyHC1 did not change. No difference was found at the mRNA and protein levels of SERCA and MyHC isoforms in the whole soleus, except that the level of the SERCA2a protein specifically declined in stz-rats compared to the controls. This shows that the coordinated expression of SERCA2a and MyHC1 is disrupted at the SERCA2a protein level in the diabetic soleus. The results are in line with previous observations that regulators of the Ca-homeostasis may adapt faster to type I diabetes than the contractile elements.
This article summarizes current knowledge on the genetics and possible molecular mechanisms of human pathologies resulted from mutations within the genes encoding several myosin isoforms. Mutations within the genes encoding some myosin isoforms have been found to be responsible for blindness (myosins III and VIIA), deafness (myosins I, IIA, IIIA, VI, VIIA and XV) and familial hypertrophic cardiomyopathy (β cardiac myosin heavy chain and both the regulatory and essential light chains). Myosin III localizes predominantly to photoreceptor cells and is proved to be engaged in the vision process in Drosophila. In the inner ear, myosin I is postulated to play a role as an adaptive motor in the tip links of stereocilia of hair cells, myosin IIA seems to be responsible for stabilizing the contacts between adjacent inner ear hair cells, myosin VI plays a role as an intracellular motor transporting membrane structures within the hair cells while myosin VIIA most probably participates in forming links between neighbouring stereocilia and myosin XV probably stabilizes the stereocilia structure. About 30% of patients with familial hypertrophic cardiomyopathy have mutations within the genes encoding the β cardiac myosin heavy chain and both light chains that are grouped within the regions of myosin head crucial for its functions. The alterations lead to the destabilization of sarcomeres and to a decrease of the myosin ATPase activity and its ability to move actin filaments.
Aktyna i miozyna to białka kojarzone przede wszystkim z ich kluczową rolą w generacji skurczu mięśni. Natomiast poza izoformami charakterystycznymi dla mięśni są również izoformy aktyny i miozyny, które występują we wszystkich typach komórek i tkanek (patrz artykuł Suszek i współaut. w tym zeszycie KOSMOSU). Badania prowadzone w ostatnich dwóch dekadach wykazały niezbicie, że zarówno aktyna (i szereg białek wiążących aktynę) oraz liczne miozyny (przedstawiciele rodzin I, II, V, VI, XVI i XVIII) lokalizują się w jądrze komórkowym gdzie są zaangażowane w procesy transkrypcji i naprawy DNA, transport w nukleoplazmie oraz import i eksport jądrowy, a także w utrzymywanie architektury jądra. Niniejszy artykuł opisuje dotychczasowy stan wiedzy o roli układu akto-miozynowego w jądrze komórkowym.
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Actin and myosins are the proteins mainly known from their key roles in muscle contraction. However, besides typical muscle isoforms there are actins and myosins that are present in all cell and tissue types. Studies performed within the last two decades have irrefutably shown that both the cytoplasmic actin isoforms (along with numerous actin-binding proteins) as well as many myosins (representing class I, II, V, VI, XVI and XVIII) are present within the nucleus. They play important roles in nuclear processes as they are involved in transcription and DNA repair, intranuclear transport as well as nuclear import and export, and in maintenance of nuclear architecture. This article describes the current knowledge on the acto-myosin system in this biggest cellular compartment.
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