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Three dimensional configuration of the secretory pathway and segregation of secretion granules in the yeast Saccharomyces cerevisiae

Alain Rambourg1, Catherine L. Jackson2,* and Yves Clermont3

1 Département de Biologie Cellulaire et Moléculaire, CEA/Saclay, F-91191 Gif-sur-Yvette, France
2 Cell Biology and Metabolism Branch, NICHD, NIH, Bldg. 18T, Room 101, 18 Library Drive, Bethesda, MD 20892-5430, USA
3 Department of Anatomy and Cell Biology, McGill University, 3640 University Street, Montréal, Québec, H3A 2B2, Canada



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  		Fig. 1. Three stereopairs of 0.20 µm thick sections of wild-type S. cerevisiae cells grown at 24°C. (a) Shows a nucleus (N) delimited by a lightly stained nuclear envelope in continuity with ER sheets or ribbons seen in side view (ER). One of these ER elements is continuous (arrow) with a strongly stained tubular network, probably a Golgi element (G). Another sheet of ER seen in face view (er) is in close proximity to another strongly stained tubular network showing more intensely stained nodular dilations (G). Intensely stained free secretion granules (SG) are interspersed throughout the cytoplasm. CW, cell wall. Magnification x18,800. (b) Lightly stained ER ribbons are seen in oblique or side views (ER). Strongly stained structures resembling secretion granules (white arrow) are observed at the left-hand extremity of an obliquely sectioned ER ribbon. Spherical membranous structures (V) resembling vacuoles are in close contact with the nuclear envelope. N, nucleus. Magnification x40,500. (c) A non-perforated ER sheet (ER) seen in face view is continuous at its periphery with lightly stained anastomosed tubules (arrows) forming a wide-meshed tubular network. At the right-hand side extremity of this network, there are more intensely stained dilations (arrowheads) that resemble secretion granules (SG). Magnification x74,000.

 


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  		Fig. 2. Tubular networks and secretion granules in 0.20 µm thick sections of wild-type S. cerevisiae cells. (a) A wide-meshed tubular network (arrows) is connected to an ER ribbon seen in side view (ER). Nodular dilations of variable staining are shown at arrowheads. Magnification x70,000. (b) A wide-meshed lightly stained tubular network (arrow) is seen just below the cell wall. Heavily stained dilations (arrowheads) are present at the intersections of tubules making up a Golgi network with narrower polygonal meshes (G). CW, cell wall. Magnification x66,800. (c) A tubular network (arrow) with dilations (arrowhead) is observed next to the subplasmalemmal ER (ER). The nucleus (N) is delimited by the lightly stained nuclear envelope. Magnification x72,600. (d) A wide-meshed tubular network (arrow) with an intensely stained dilation (arrowhead) is adjacent to the nucleus (N). ER, ER ribbon; SG, free secretion granules. Magnification x32,200. (e) Next to a tubular network (vertical arrow) seen side view there are secretion granules bridged by thin faintly stained tubules (arrowheads). A portion of the strongly reactive cell wall is seen at the bottom-right. V, small vacuole-like structure. Magnification x36,300. (f) Numerous secretion granules (SG) are clustered in the bud of a growing cell. Several granules are still connected (arrowhead). The cell wall is strongly stained (CW). Magnification x81,100.

 


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  		Fig. 3. Spherical and cylindrical structures in 0.20 µm thick sections of wild-type S. cerevisiae cells grown at 37°C. (a) A poorly perforated sheet of endoplasmic reticulum curves (ER) and forms a cylindrical structure (white arrow). A large, well-stained vacuole (V) is located adjacent to the nucleus (N). Magnification x38,500. (b) Three vacuole-like spherical structures (V) are connected to the nuclear envelope (N). The vacuole structure at the top-right is continuous with a sheet of unperforated ER (ER). A tubular network (arrow) is also labeled. Magnification x52,400. (c) Connected to the nuclear envelope, an unperforated ER sheet (ER) forms cylindrical structures (arrows). N, nucleus. Magnification x67,400.

 


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  		Fig. 4. erg6 strain treated for 5 minutes with BFA. (a) A tubular Golgi network with small dilations at the intersections of polygonal meshes (G) is seen next to a curved sheet of unperforated ER (er). At the left, a tubular network (white arrow) is seen in profile and is continuous with a portion of subplasmalemmal ER at the top-left. A small vacuole-like structure (V) is located next to the nucleus (N). Magnification x39,700. (b) Several small vacuole-like structures of variable staining densities (V) are in close contact with the nuclear envelope. At the bottom-left, one of these structures is continuous with an ER sheet (ER). A large intensely stained vacuole (*) is seen proximal to the nucleus (N). Magnification x38,500. (c) Next to the nucleus (N) and connected to a subplasmalemmal ER sheet (ER), there is a large tubular network (arrow) forming an ovoid mass. Light and dense vacuoles are also labeled (V). Magnification x40,100. (d) A tubular Golgi network with small dilations at the intersections of narrow, irregular meshes (G) is continuous at one side with a wide-meshed tubular network (arrow) and is connected on the right with a parallel array of anastomosed tubules (white arrow). N, nucleus. Magnification x43,350. (e) A parallel array of saccules (white arrow) is seen in proximity to an ER sheet (ER). A large vacuole is labeled (V). Magnification x82,100.

 


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  		Fig. 5. sec21-3 mutant maintained for 5 minutes (a) and 20 minutes (b) at 37°C, blocked for 20 minutes at 37°C and returned for 5 (c,d) or 10 minutes (e,f,g) to permissive temperature (24°C). (a) After 5 minutes at 37°C, tubular fragments with nodular dilations (arrowhead) are interspersed within the cytoplasm. An ovoid mass made up of interconnected short ribbon-like ER elements (*) is continuous with the nuclear envelope. V, small vacuole; N, nucleus; SG, free secretion granules. Magnification x40,800. (b) After 20 minutes at 37°C, the secretion granules and tubular fragments with or without dilations are no longer seen. A mass of interconnected ribbon-like ER elements (*) forms a bridge between the nuclear envelope and the subplasmalemmal ER at the top-right. Two vacuole-like structures (V) are present next to the nucleus (N). Magnification x35,400. (c) As early as 5 minutes after shifting the temperature down to 24°C, fenestrations (white arrow) and tubular networks (arrow) with dilations (arrowheads) are seen at the periphery of an unperforated sheet of ER, which is itself continuous with the subplasmalemmal ER (ER). Magnification x42,000. (d) After 5 minutes at 24°C, a tubular network (arrow) with more intensely stained dilations (arrowhead) is observed. SG, a free secretion granule; CW, cell wall. Magnification x48,000. (e) At 10 minutes after shifting the cells back to 24°C, numerous secretion granules (SG) are interspersed within the cytoplasm and accumulate in the bud on the right. At the center left, an ER sheet seen in face view shows peripheral tubules (arrow) and dilations (arrowheads) with size and staining properties similar to those of secretion granules. Magnification x59,100. (f) After 10 minutes at 24°C, a broken tubular network, presumably a Golgi element (G), with dilations of various sizes and staining intensities is observed at the top-left. SG, free secretion granules; ER, an ER sheet with a fenestrated periphery. Magnification x35,000. (g) Small poorly contrasted vacuole-like structures (*) accumulate inside or in close proximity to a large intensely reactive vacuole (V). Magnification x23,300.

 

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