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Christopher A. Fraker Camillo Ricordi Luca Inverardi Juan Domínguez‐Bendala 《Biology of the cell / under the auspices of the European Cell Biology Organization》2009,101(8):431-440
Beyond its role as an electron acceptor in aerobic respiration, oxygen is also a key effector of many developmental events. The oxygen‐sensing machinery and the very fabric of cell identity and function have been shown to be deeply intertwined. Here we take a first look at how oxygen might lie at the crossroads of at least two of the major molecular pathways that shape pancreatic development. Based on recent evidence and a thorough review of the literature, we present a theoretical model whereby evolving oxygen tensions might choreograph to a large extent the sequence of molecular events resulting in the development of the organ. In particular, we propose that lower oxygenation prior to the expansion of the vasculature may favour HIF (hypoxia inducible factor)‐mediated activation of Notch and repression of Wnt/β‐catenin signalling, limiting endocrine cell differentiation. With the development of vasculature and improved oxygen delivery to the developing organ, HIF‐mediated support for Notch signalling may decline while the β‐catenin‐directed Wnt signalling is favoured, which would support endocrine cell differentiation and perhaps exocrine cell proliferation/differentiation. 相似文献
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Changes in Targeting Efficiencies of Proteins to Plant Microbodies Caused by Amino Acid Substitutions in the Carboxy-terminal Tripeptide 总被引:7,自引:0,他引:7
Hayashi Makoto; Aoki Masahiro; Kondo Maki; Nishimura Mikio 《Plant & cell physiology》1997,38(6):759-768
It has been demonstrated that the carboxyl terminus of microbodyenzymes functions as a targeting signal to microbodies in higherplants. We have examined an ability of 24 carboxy-terminal aminoacid sequences to facilitate the transport of a cytosolic passengerprotein, ß-glucuroni-dase, into microbodies in greencotyledonary cells of trans-genic Arabidopsis. Immunoelectronmicroscopic analysis revealed that carboxy-terminal tripeptidesequences of the form [C/A/S/P]-[K/R]-[I/L/M] function as amicrobody-targeting signal, although tripeptides with prolineat the first amino acid position and isoleucine at the carboxylterminus show weak targeting efficiencies. All known micro-bodyenzymes that are synthesized in a form similar in size to themature molecule, except catalase, contain one of these tripeptidesequences at their carboxyl terminus. (Received April 14, 1997; Accepted April 8, 1997) 相似文献
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Human chorionic gonadotropins (hCGs) highly purified from the urine of patients with trophoblastic diseases and of healthy pregnant women contain approximately four mucin-type sugar chains in one molecule. The structures of these sugar chains were studied comparatively by using a new sensitive method to obtain mucin-type sugar chains quantitatively as radioactive oligosaccharides from a small amount of glycoproteins. The mucin-type sugar chains of all hCGs include sialylated and nonsialylated Gal beta 1----3GalNAc and Gal beta 1----4GlcNAc beta 1----6(Gal beta 1----3)GalNAc. In the case of normal hCG and hydatidiform mole hCG, oligosaccharides containing the tetrasaccharide core occupy approximately 10% of the total mucin-type sugar chains. The ratio of the tetrasaccharide containing oligosaccharides is increased prominently to approximately 60% in choriocarcinoma hCG. The proportion in invasive mole hCG was also increased, but less than the proportion of choriocarcinoma hCG. 相似文献
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Functional expression of the calcium release channel from skeletal muscle ryanodine receptor cDNA 总被引:7,自引:0,他引:7
Combined patch-clamp and fura-2 measurements were performed to study the calcium release properties of Chinese hamster ovary (CHO) cells transfected with the rabbit skeletal muscle ryanodine receptor cDNA carried by an expression vector. Both caffeine (1-50 mM) and ryanodine (100 microM) induced release of calcium from intracellular stores of transformed CHO cells but not from control (non-transfected) CHO cells. The calcium responses to caffeine and ryanodine closely resembled those commonly observed in skeletal muscle. Repetitive applications of caffeine produced characteristic all-or-none rises in intracellular calcium. Inositol 1,4,5-trisphosphate (IP3) neither activated the ryanodine receptor channel nor interfered with the caffeine-elicited calcium release. These results indicate that functional calcium release channels are formed by expression of the ryanodine receptor cDNA. 相似文献
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Procathepsin H in kidney and liver microsomal lumen was identified to have a molecular mass of 41 kDa by immunoblot analysis. The proenzyme was then concentrated by applying the microsomal contents to a concanavalin A-Sepharose column. When the concanavalin A-adsorbed fraction was incubated at pH 4.0 at 20 degrees C, the activity measured with synthetic substrate increased 3.5 times over that of the control after 24 h incubation. Immunoblot analysis showed that acidic treatment caused the disappearance of procathepsin H. Thus the proenzyme might be processed to the mature enzyme under acidic conditions. The marked increase of enzymatic activity and the conversion of proenzyme were completely blocked with pepstatin which is a potent inhibitor of aspartic proteases. These results suggested that a protease for processing procathepsin H might be cathepsin D, a major lysosomal aspartic protease. Therefore, procathepsin H seems to be synthesized first in the enzymatically inactive form in endoplasmic reticulum and successively converted into the active form in lysosomes during biosynthesis. 相似文献
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