| dc.contributor.author | Abran, Daniel. | en_US |
| dc.date.accessioned | 2014-10-21T12:35:02Z | |
| dc.date.available | 1991 | |
| dc.date.issued | 1991 | en_US |
| dc.identifier.other | AAINN71471 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55259 | |
| dc.description | Myeloid bodies (MBs) are organelles which are continuous with the smooth endoplasmic reticulum (SER) membranes within the retinal pigment epithelium (RPE) of a number of lower vertebrates. Also, MB numbers in the RPE of the newt have been temporally correlated with phagocytosis of outer segment (OS) disc membranes in previous studies. To test the hypothesis that MBs are directly involved in OS lipid metabolism, I compared the phospholipid composition of a MB-enriched subcellular fraction of chick retinal pigment epithelium (RPE) with that of chick rod outer segments (ROS). The major phospholipids found in MBs were phosphatidylcholine and phosphatidylethanolamine which represented 43% and 34% of the total MB lipids respectively. Sphingomyelin and phosphatidylinositol comprised the remaining detectable phospholipids in MBs. The fatty acyl chain composition of all detected phospholipids showed that the long-chain polyunsaturated fatty acids, 20:4 n-6, 22:5 n-3 and 22:6 n-3, accounted for more than 45% of the fatty acids in MB membranes. The ROS contained, in addition to the phospholipids found in MBs, phosphatidylserine and lyso-phosphatidyl-choline. Further, the distribution of the fatty acids in ROS phospholipids differed substantially from the ones in MBs, especially for 22:6 n-3 and 22:5 n-3. The results from this study demonstrated that chick MBs had a different phospholipid and fatty acid composition than chick ROS. However, they both represent a significantly enriched pool of essential polyunsaturated fatty acids. | en_US |
| dc.description | I also examined the effects on MBs of eliminating the source of OS membrane lipids (neural retina removal) and of the subsequent return of OS (retinal regeneration) in the newt (Notophthalmus viridescens) in order to further characterize the origin and functional significance of these organelles. Light and electron microscopic analysis demonstrated that within six days of neural retina removal, MBs disappeared from the RPE. By the sixth week of regeneration, rudimentary photoreceptor OS were present MBs were still absent from the RPE. However, at this time, the SER in some areas of the RPE cells had become flattened, giving rise to small (0.5 $\mu$m long), two to four layer-thick lamellar units which we have described as MB templates. Small MBs were first observed one week later, at the seventh week of retinal regeneration. | en_US |
| dc.description | This study has revealed that newt MBs are specialized areas of SER. It also showed that contact between functional photoreceptors and the RPE is essential to the presence of MBs in the RPE cell. Although the phospholipid and fatty acid analysis of chick MBs did not conclusively establish the expected link between MBs and ROS, it pioneered an isolation protocol for MBs and provided invaluable information on MB membrane composition as well as suggesting a possible role for MBs in the recycling of essential fatty acids from photoreceptor OS. These findings will, I hope, offer new directions to the search for MBs function in the RPE. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1991. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Biology, Cell. | en_US |
| dc.subject | Chemistry, Biochemistry. | en_US |
| dc.title | Phospholipid composition and genesis of myeloid bodies of the retinal pigment epithelium. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
