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PubMed1978

Cell death in the posterior necrotic zone (PNZ) of the chick wing-bud: a stereoscan and ultrastructural survey of autolysis and cell fragmentation.

The participation of lysosomes and cell profile changes were studied during mesenchymal cell death in the PNZ of forelimbs of the 4 1/2-day chick embryo. Lysosome participation was studied cytochemically using as substrate either beta-glycerophosphate or p-nitrophenylphosphate. Acid phosphatase (AP) is localized within the Golgi cisternae of the prospective dying cells, and small AP-positive autophagic vacuoles appear when degeneration commences. As degeneration by enzymic digestion proceeds, these vacuoles increase in size and appear to become autolytic since part of the AP activity seems to 'leak' out of the autophagic vacuoles. Next, the cells fragment and the fragments are then enclosed in heterophagic vacuoles of macrophages where digestion is completed. The SEM showed that these intracellular changes in degenerating cells are accompanied by changes in the cell surface structure. First, the degenerating cells lose the stellate appearance of healthy mesenchymal cells and become rounded and pitted, then constrictions appear and finally the cytoplasm breaks up into many small pieces. This final fragmentation may be an active process rather than a mere consequence of vacuolation.

Acid Phosphatase↗
PubMed1993

Muscle-specific calpain, p94, is degraded by autolysis immediately after translation, resulting in disappearance from muscle.

We previously identified a third type of the calpain large subunit named p94 as a cDNA whose mRNA is expressed exclusively in skeletal muscle at levels approximately 10-fold more abundant than those of the conventional calpain subunit. Rat skeletal muscle fractions were screened by two anti-peptide antibodies raised against two specific sequences in p94, but the p94 protein could not be found. To examine this apparent discrepancy between the amounts of mRNA and protein, wild-type p94 was expressed in COS cells. Although p94 mRNA was expressed normally in COS cells, only very small amounts of the protein and its presumed degradation products were detected by the antibodies described above. A series of COOH-terminal deletion mutants was constructed and expressed in COS cells and L8 cells, a rat myoblast cell line. When IS2, one of the specific regions of p94, was completely eliminated, the truncated p94 proteins were expressed normally, and the amount of the expressed proteins was at least 100-fold higher than with wild-type p94. Moreover, when site-directed mutagenesis was introduced to change the presumed active-site cysteine of p94 to serine or alanine, the mutated p94 proteins were highly expressed like the IS2-deleted mutants. These results indicate the following. 1) The mRNA for p94 is normally transcribed in COS, L8, and muscle cells; 2) the p94 protein becomes active in the cytosol immediately after translation; 3) the p94 protein virtually disappears from cells by autocatalytic degradation; and 4) the p94-specific IS2 region plays an important role in this degradation. In vitro translation experiments support this idea. Furthermore, p94 shows nuclear localization when expressed in COS cells. The physiological function of p94 in muscle is discussed on the basis of the analysis of these transfectants.

Amino Acid Sequence↗
PubMed1991

Auxin-enhanced glucan autohydrolysis in maize coleoptile cell walls.

Cell walls isolated from auxin-pretreated maize (Zea mays L.) coleoptile segments were assayed to disclose evidence for the existence of enhanced autolysis. To improve the sensitivity of the measurements and to facilitate kinetic analysis, isolated cell walls were consolidated within a small column, and the autolysis rate was directly determined from the sugar content of the effluent. This protocol revealed that the maximum rate of autohydrolysis of walls prepared from segments occurs within the first 2 hours and a steady decline commences almost immediately. Walls from indoleacetic acid pretreated segments (0.5-4 hours) released sugar at a higher rate initially (110-125% of controls) and the enhanced rate of autolysis continued for 6 to 8 hours, but then it became equivalent to that of the controls. Pretreatment of the segments at acidic pH had no effect on the measurable rates of autolysis. The (1-->3), (1-->4)-beta-d-glucan content of the walls and the extractable glucanase activities support the hypothesis that temporal enhancement of autohydrolysis is a function of auxin on enzyme activity. The progressive decline in autolysis during prolonged incubations is consistent with the decrease in the quantity of the beta-d-glucan in the wall. The relationship between glucan content and autolysis rate is supported by the observation that while glucose pretreatment of segments had only a small effect on initial autolysis rates, the presence of the sugar during pretreatment served to extend the interval over which higher rates of autolysis could be sustained. The results demonstrate that autolysis is related to auxin-induced wall metabolism in maize coleoptiles.

Journal Article↗