ERES (ER exit sites) and the "secretory unit concept"

The higher plant Golgi apparatus consists of hundreds of individual Golgi stacks which move along the cortical ER, propelled by the actomysin system. Anterograde and retrograde transport between the endoplasmic reticulum (ER) and the plant Golgi occurs over a narrow interface (around 500 nm) and is generally considered to be mediated by COP-coated vesicles. Previously, ER exit sites (ERES) have been identified on the basis of to localization of transiently expressed COPII-coat proteins. As a consequence it has been held that ERES in higher plants are intimately associated with Golgi stacks, and that both move together as an integrated structure: the "secretory unit". Using a new COPII marker, as well as YFP-SEC24 (a bona fide COPII coat protein), we have made observations on tobacco leaf epidermis at high resolution in the CLSM. Our data clearly shows that COPII fluorescence is associated with the Golgi stacks rather than the surface of the ER and probably represents the temporary accumulation of COPII vesicles in the Golgi matrix prior to fusion with the cis-Golgi cisternae. We have calculated the numbers of COPII vesicles which would be required to provide a typical Golgi-associated COPII-fluorescent signal as being much less than 20. We have discussed the consequences of this and question the continued usage of the term "secretory unit".     

Immunophenotyping of lymphocyte subsets in the third eyelid tissue in dogs (Canis familiaris): morphological, microvascular, and secretory aspects of this ocular adnexa

The third eyelid is an important adnexa of the eye. The objective of this study was to evaluate (i) morphological aspects (ii) vascularization, and (iii) the immunophenotype of lymphocyte subsets in the third eyelid of dogs. Flow cytometric analysis revealed the presence of three patterns concerning the immunophenotype of the third eyelid tissue. Dogs without ocular insult or deficient tear production might belong to one of the following immunophenotype patterns: I--the number of T-cells that expressed CD3(+) CD8(+) was higher than the number of cells that expressed CD3(+)CD4(+). II--the number of cells CD3(+)C4(+) was higher than the number of cells CD3(+)CD8(+) and in this case a higher number of cells that expressed CD19 were identified. III--Proximity of values of the cells that expressed CD3(+)CD4(+) and CD3(+)CD8(+). These data might suggest that the number of lymphocyte T cells alone should not be considered a direct indicator of the presence of an immune-based inflammation. Besides, a particular population of T-cells does not indicate a particular inflammatory state. The morphological study of the third eyelid revealed a rather uncommon angioarchitecture. The artery that irrigates the eyelid crosses almost the entire length of this structure to achieve its free border, and only then, ramificates deeply towards an inner segmental level. This spatial microvascular arrangement probably results from an adaptation to the fact that the third eyelid, in the medial cantus of the eye, is inwardly compressed into a tiny space. Efficient vascularization is achieved by allowing the first ramifications of the third eyelid artery to run straight to the top. Accini secretor cells of the third eyelid show a mucin content while tubuloacinar cells are mainly serous.