The function of the golgi apparatus in lactating cells of the balb/cCrgl mouse

123

In the mammary glands of lactating albino mice injected intravenously with 9, 10-oleic acid-3 H or 9,10-palmitic acid-5 H, it has been shown that the labeled fatty acids are incorporated into mammary gland glycerides. The labeled lipid in the mammary gland min after injection was in esterified form ( > 95%), and the radioautographic reaction was seen over the rough endoplasmic reticulum and over lipid droplets, both intracellular and intraluminal. At 10-60 min after injection, the silver grains were concentrated predominantly over lipid droplets. There was no concentration of radioactivity over the granules in the Golgi apparatus, at any time interval studied. These findings were interpreted to indicate that after esterification of the fatty acid into glycerides in the rough endoplasmic reticulum an in situ aggregation of lipid occurs, with acquisition of droplet form. The release of the lipid into the lumen proceeds directly and not through the Golgi apparatus, in contradistinction to the mode of secretion of casein in the mammary gland or of lipoprotein in the liver. The presence of strands of endoplasmic reticulum attached to intraluminal lipid droplets provides a structural counterpart to the milk microsomes described in ruminant milk INTRODUCTION

Section: Discussionsupporting

confidence: 67%

Lipid Synthesis, Intracellular Transport, and Secretion

Stein

1967

123

“…The 2minute pattern indicated that the site of protein synthesis was the rER . Presumably, as in other cells, protein synthesis took place in relation to ribosomes (38)(39)(40)(41)(42)(43)(44)(45)(46) . Between 2 and 10 min after tyrosine-3H injection, there was a sharp drop in the radioactivity of the rER, while the total radioactivity did not decrease .…”

Section: Production Of Proteinmentioning

confidence: 97%

The Elaboration of Protein and Carbohydrate by Rat Parathyroid Cells as Revealed by Electron Microscope Radioautography

Nakagami

Warshawsky

Leblond

1971

The parathyroid glands of young rats were radioautographed after a single injection of the protein precursor tyrosine-8H in the hope of identifying the sites of synthesis and migration of newly formed protein in the gland cells . The same procedure was used after injection of the glycoprotein precursor galactose3H . As early as 2 min after intravenous injection of tyrosine-1 H, the label was mainly found in the rough endoplasmic reticulum suggesting that cisternal ribosomes are sites of protein synthesis . By 5 and 10

“…The same sequence seems to operate in glandular cells specialized in the synthesis of proteins for export, provided the secretory product is quantized and stored temporarily in the cell in concentrated form. For example, radioautographic evidence suggests that the model applies to the mammary gland (Wellings and Philp, 1964), and to myelocytes (Fedorko and Hirsch, 1966). In cells in which there is no intracellular accumulation of secretory product or in which the latter accumulates within the ER cisternae (Ross and Benditt, 1965;Revel and Hay, 1963;Rifkind et al, 1962), the extent to which the Golgi complex is involved is not clear.…”

Section: Tory Proteinsmentioning

confidence: 99%

Intracellular Transport of Secretory Proteins in the Pancreatic Exocrine Cell

Jamieson

Palade

1967

592

106

In the previous paper we described an in vitro system of guinea pig pancreatic slices whose secretory proteins can be pulse-labeled with radioactive amino acids. From kinetic experiments performed on smooth and rough microsoines isolated by gradient centrifugation from such slices, we obtained direct evidence that secretory proteins are transported from the cisternae of the rough endoplasmic reticulum to condensing vacuoles of the Golgi complex via small vesicles located in the periphery of the complex. Since condensing vacuoles ultimately become zyniogen granules, it was of interest to study this phase of the secretory cycle in pulse labeled slices. To this intent, a zymogen granule fraction was isolated by differential centrifugation from slices at the end of a 3-min pulse with leucine-1 4C and after varying times of incubation in chase medium. At the end of the pulse, few radioactive proteins were found in this fraction; after +17 min in chaser, its proteins were half maximally labeled; they became maximally labeled between +37 and +57 min. Parallel electron microscopic radioautography of intact cells in slices pulse labeled with leucine-3H showed, however, that zymogen granules become labeled, at the earliest, +57 min post-pulse. We assumed that the discrepancy between the two sets of results was due to the presence of rapidly labeled condensing vacuoles in the zymogen granule fraction. To test this assumption, electron microscopic radioautography was performed on sections of zymogen granule pellets isolated from slices pulse labeled with leucine-3H and subsequently incubated in chaser. The results showed that the early labeling of the zymogen granule fractions was, indeed, due to the presence of highly labeled condensing vacuoles among the components of these fractions.