Several methods may be used to assess stem cell competence, including the expression of cell surface markers and telomerase activity. We hypothesized that mitochondrial characteristics might be an additional and reliable way to verify stem cell competence. In a multipotent, adult monkey stromal stem cell line, previously shown to differentiate into adipocytes, chondrocytes, and osteocytes, we found that several mitochondrial properties change with increasing passage number in culture. Cells from the earliest passage (P11) versus those from a later passage (P17) are characterized by: (a) a much higher percentage of cells (85% vs. 18%) with a perinuclear arrangement of mitochondria; (b) a much lower percentage of cells (1% vs. 57%) with an aggregated mitochondrial arrangement, in which mitochondria appear to coalesce into large clumps; (c) a much lower percentage of cells with lipid droplets (1% vs. 36%), suggesting less differentiation into adipocytes; (d) a 5.6-fold lower ATP content per cell (0.45 vs. 2.51 pmoles ATP/cell; and (e) a 10-fold higher rate of oxygen consumption (37.8 vs. 3.8 nmoles O2/min/10(3) cells), indicating a higher metabolic activity. Collectively, these data indicate that the perinuclear arrangement of mitochondria, accompanied by a low ATP/cell content and a high rate of oxygen consumption, may be valid indicators of stem cell differentiation competence, while departures from this profile indicate that cells are differentiating or perhaps becoming senescent. These results represent the first characterization of mitochondrial properties reported for a primate stem cell line.
The current status of knowledge about mitochondrial properties in mouse, monkey and human embryonic, adult and precursor stem cells is discussed. Topics include mitochondrial localization patterns, oxygen consumption and ATP content in cells as they relate to the maintenance of stem cell properties and subsequent differentiation of stem cells into specific cell types. The significance of the perinuclear arrangement of mitochondria, which may be a characteristic feature of stem cells, as well as the expression of mitochondrial DNA regulatory proteins and mutations in the mitochondrial stem cell genome is also discussed.
The opening of excised Samnea saman pulvini is promoted by prolonged blue or far-red irradiation. Far-red effects are attributed partially but not completely to lowering of the Pfr level. Two hours of continuous or pulsed blue light or pulsed far-red Ught (total dosage = 2.2 x 1018 quanta per square centimeter in all cases) also phase shifts the rhythm in Samanea while two hours of continuous blue Ught phase shifts the rhythm in the related plant Albizzia julibrissin. The same pigments appear to regulate opening and rhythmic phase shifting. The blue light-induced phase response curve has smafler advance and delay peaks and differs in shape from the curve induced by brief red light pulses absorbed by phytochrome. The blue absorbing pigment has not been identified, but it does not appear to be phytochrome acting in a photoreversible mode.
Rhythmic changes in the light reactions of Euglena gracilis have been found which help to explain the basic reactions effected in the circadian rhythm of 02 evolution. Diurnal changes in the slope of light intensity plots indicated that the maximal rate of photosynthesis changed throughout the circadian cycle. No evidence was obtained consistent with the premise that changes in chlorophyl content, as measured by total chlorophyl or chlorophyUl a/b ratio, or photosynthetic unit size are responsible for this rhythm.The rate of light-induced electron flow through the entire electron chain (H20 to methyl viologen) was rhythmic both in whole cells and in isolated chloroplasts, and the highest rate of electron flow coincided with the highest rate of 02 evolution. The individual activities of photosystem I (reduced form 2,6-dichlorophenol-indophenol to methyl viologen) and photosystem II (H20 to 2,6"dichlorophenol-indophenol) did not, however, change significantly with time of day, suggesting that the coordination of the two photosystems may be the site of circadian control. Evidence consistent with this concept was obtained from studies of low temperature emission from systems I and II folowing preillumination with system I or II light.A circadian rhythm of photosynthetic 02 evolution has been observed in several eukaryotic organisms (16) including Euglena (22). The mechanisms responsible for this rhythm have been investigated but never fully elucidated. Steady-state 02 evolution in whole cells is a function of both the light reactions and the enzyme activities of the Calvin cycle. The photosynthetic rhythm, however, does not seem attributable to rhythmic changes in the activity of any Calvin cycle enzyme (8, 15,22). Therefore, the light reactions would appear to be the most probable oscillator-controlled part of photosynthesis.Many
A circadian rhythm of 02 evolution has been found in E.glena gracilis, Klebs strain Z. The rhythm persists for at least 5 days in constant dim ligt and temperature, but damps out in constant bright libt. The phase of this rhythm can be shifted by a pulse of bright lght and the period length is not changed over a 10 C span of growth temperature.The 02 evolution rhythm is found in both logrthmic and stationary phase cultures, but CO2 uptake is dearly rhythmic only in stationary phase cultures.The activity of glyceraldebyde-3-phosphate debydrogenase was not rhythmic as previoudy reported (Walther and Edmunds [19731 Plant Physiol. 51: 250258). Carbonic anhydrase activity was rhythmic when the cultures were ma ned der a lght-dark cycle with the highest enzyme activity coinciding with the fastest rate of 02 evolution. However, the rhythm in carbonic anhydrase activity diappeared under constant conditions. Changes in the activities of these two enzymes are tberefore not responsible for the rhythmic changes in photosynthetic capacty.Circadian rhythms in photosynthesis have been observed in several algae and higher plants (12). The mechanism(s) responsible for the rhythms of 02 evolution and CO2 fixation have never been resolved, even though most aspects of the light and dark reactions have been investigated (3,11,(17)(18)(19)22). This problem has been reinvestigated using the single cell alga Euglena gracilis in an attempt to explain how the 02 evolution rhythm is regulated.Daily oscillations in photosynthesis have been reported for Euglena (22), but it was not established that a persistent circadian rhythm was involved. This investigation shows by several criteria that the rhythm of 02 evolution in Euglena can be circadian. A careful description of this rhythm is given here since this work is the basis for several forthcoming papers dealing with the mechanism of the photosynthetic rhythm.Several investigators have tried to determine if rhythmic changes in the activity of the Calvin cycle enzymes are responsible for the photosynthesis rhythm (3,11,19,22). The activity of ribulose-1,5-bisP carboxylase is not rhythmic in Euglena (4,22) or other algae (3, 11). Walther and Edmunds reported that
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