Accumulating data suggest that the oligodendrocyte population includes morphological and biochemical subtypes. We recently reported that a polyclonal antiserum against an unknown antigen, the T4-O ...molecule, labels a subpopulation of chicken oligodendrocytes, obviously representing the type IV variety of Del Rio Hortega. The present study examines the developmental expression of the T4-O molecule in situ and in vitro. The results show that T4-O immunoreactive cells first appear at E15 in the ventral funiculus. But, oligodendrocytes cultured in vitro with or without neurones do not develop a T4-O immunoreactivity. We conclude that oligodendrocytes in the spinal cord of chicken embryos first express the T4-O molecule some time after onset of myelination, and that the T4-O immunoreactive phenotype does not develop in vitro.
Axonal pathology in myelin disorders Bjartmar, C; Yin, X; Trapp, B D
Journal of neurocytology,
04/1999, Letnik:
28, Številka:
4-5
Journal Article
Myelination provides extrinsic trophic signals that influence normal maturation and long-term survival of axons. The extent of axonal involvement in diseases affecting myelin or myelin forming cells ...has traditionally been underestimated. There are, however, many examples of axon damage as a consequence of dysmyelinating or demyelinating disorders. More than a century ago, Charcot described the pathology of multiple sclerosis (MS) in terms of demyelination and relative sparing of axons. Recent reports demonstrate a strong correlation between inflammatory demyelination in MS lesions and axonal transection, indicating axonal loss at disease onset. Disruption of axons is also observed in experimental allergic encephalomyelitis and in Theiler's murine encephalomyelitis virus disease, two animal models of inflammatory demyelinating CNS disease. A number of dysmyelinating mouse mutants with axonal pathology have provided insights regarding cellular and molecular mechanisms of axon degeneration. For example, the myelin-associated glycoprotein and proteolipid protein have been shown to be essential for mediating myelin-derived trophic signals to axons. Patients with the inherited peripheral neuropathy Charcot-Marie Tooth disease type 1 develop symptomatic progressive axonal loss due to abnormal Schwann cell expression of peripheral myelin protein 22. The data summarized in this review indicate that axonal damage is an integral part of myelin disease, and that loss of axons contributes to the irreversible functional impairment observed in affected individuals. Early neuroprotection should be considered as an additional therapeutic option for these patients.
Gametophytes of five geographically diverse populations of the moss Polytrichum commune ranging from Barrow, Alaska (71°N), to Gainesville, Florida (29°N), were grown under constant temperatures of ...5° and 20°C with 16 h of light each day. The net CO₂ exchange of the shoot tissue produced under these conditions was subsequently studied in relation to temperature. The following patterns were noted. (1) The maximum net photosynthetic rate decreased in P. commune populations from sites along a gradient of increasing latitude, except that highest rates were found in the temperature St. Hilaire population; the difference in photosynthetic rates between the extreme values was about sevenfold, (2) Cool growth conditions resulted in low maximum net CO₂ uptake rates. (3) The growth temperature affected the maximum net photosynthetic rate of low—latitude populations more than high—latitude populations. (4) The optimum temperatures for photosynthesis were equal to or higher than the growth temperatures. (5) The temperature at the center of the estimated optimal range for net CO₂ uptake was correlated with both preconditioning temperature and the latitude of origin. (6) The upper temperature compensation points, which were unusually high for bryophytes, were correlated positively with the preconditioning temperature and negatively with the latitude of origin. (7) Northern populations had dark—respiration rates which were equal to or lower than those of southern populations. (8) After low—temperature acclimation, the dark respiration increased only in the southernmost population.
Two moss species, Polytrichum commune Hedw. and P. alpinum Hedw. growing on the tundra near Barrow, Alaska, were studied with respect to biomass partitioning, above- and belowground carbohydrate ...reserves and stem respiration. The biomass of belowground parts constituted about 30% of the total living biomass in both species. Sugar concentrations were highest in the green shoots but starch concentration was highest in belowground parts. Respiration rates were similar in the belowground parts of both species and increased linearly with temperature over the temperature range observed. The proportion of the diel carbon gain by the aboveground shoot which was respired by the belowground parts sometimes exceeded 30%. This CO2 loss is considered to affect the pattern of both the diel and seasonal CO2 uptake and result in net seasonal dry matter accumulation of about 250 mg g-1 dry weight of the whole plant. /// У двух видов мхов Polytrichum commune и P. alpinum, растущих в тундре, в окрестностях Бэрроу на Аляске, определено распределение биомассы, запас углеводов в надземных и подземных частях и дыхание стеблей. Биомасса подземных частей составляет около 30% от общей живой биомассы у обоих видов. Концентрации сахаров максимальны в зеленых побегах, но содержание крахмала наибольшее в подземных частях. Интенсивность дыхания сходна в подземных частях у обоих видов, она находится в прямой линейной зависимости от температуры в определенных температурных пределах. Доля суточного потока углерода, потпебляемого надземными побегами, превышает 30%. Эта лотепя CO2 предположительно влияет на величину суточного и сезонного потребления CO2. Чистая продукция сухого вещества за сезон составляет около 250 мг/г сухого вещества для целого растения.
Microclimatic habitat conditions and diel field CO2 flux were studied in Polytrichum alpinum and P. commune during the 1973 growing season and again in the late autumn of 1974, near Barrow, Alaska. ...Incident photon flux density differed among the three different habitats a mesic meadow, polygon center and polygon rim while differences in moss surface temperature and water content were small. Diel CO2 flux remained positive during June and much of July in unshaded samples of both species while shaded samples of P. alpinum showed night respiration and reduced daytime CO2 uptake during much of the season. The proportion of the diel assimilate pool respired at night increased sharply from first sunset on 2 August. No regular seasonal changes in maximum net photosynthetic rate could be detected in either species. Samples of P. alpinum from the shaded mesic meadow reached light compensation at lower photon flux densities than did the samples from the more open low polygon centers, especially at higher temperatures. P. commune showed a greater temperature sensitivity in net photosynthesis than P. alpinum. A seasonal total CO2 uptake of 700-800 mg g-1 is estimated for nonshaded above-ground shoots. /// Микроклиматические условия и суточная интенсивность выделения CO2 исследована у Polytrichum alpinum и P. commune в течение вегетационного сезона 1973 г. и повторно - поздней осенью 1974 г. в окрестностях Бзрроу, на Аляске. Интенсивность потока фотонов различна в 3-х разных местообитаниях - на мезофитном лугу, в центре полигона и у края полигона, где различия температурь ы поверхности мха и содепжания влаги незначительны. Сыточное выделение CO2 остается положительной величиной в июне и в течение большей части июля в незатененных пробах обоих видов, а на затененных пробах P. alpinum обнаружено ночное дыхание и сокращенное потребление CO2 бнем б течение большей части сезона. Отношение пула сыточного потреболения к ночной респирации резко возрастает от первого захода солнца 2 августа. Не установлено регулярных сезонных изменений максимальной скорости чистого фотосинтеза у отдельных видов. Пробы P. alpinum из затененного мезофитного луга достигают световой компенсации при более низкой интенсивности потока фотонов в сравнении с пробани из более открытого и низкого центра, особенно при бысоких температурах. P. commune более чувствителен к температуре по показателям чистого фотосинтеза, чем P. alpinum. Определено общее сезонное потребление CO2, составляюцее 700-800 мг/г у незатененных надземных побегов.
Two tundra Polytrichum moss species were sampled in the field near Barrow, Alaska, three times during the growing season. Lipid, sugar, and starch concentrations of the green above ground shoots and ...below ground rhizomes were analyzed. Lipid and TNC (sugar + starch) concentrations were higher in Polytrichum commune growing on raised polygon rims than in Polytrichum alpinum. There were no significant differences between the two populations of P. alpinum. Green parts had significantly higher lipid concentrations than rhizomes in P. commune but not in P. alpinum. Both species had significantly higher sugar concentration in green shoots and higher starch concentrations in the rhizome and sugar concentration varied significantly in both species. Seasonal variation of TNC concentration levels were significant only in P. commune. A statistically significant positive relationship was found between lipid and TNC concentration while a stronger statistically significant negative relationship was found between sugar and starch concentration. The first is interpreted as an adaptation to drought in surface waxes and osmoticum while the second is interpreted as conversion indicator depending on tissue and use. Polytrichum mosses resemble evergreen vascular plants in their seasonal stability of these compound groups.
