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The pinocytosis of 125I-labelled poly(vinylpyrrolidone), [14C]sucrose and colloidal [198Au]gold by rat yolk sac cultured in vitro.

ABSTRACT: The rates of uptake of 125I-labelled poly(vinylpyrrolidone), [14C]sucrose and colloidal [198Au]gold by 17.5-day rat yolk sac cultured in vitro were studied. Over a 6.5h period each substrate was accumulated at a constant and reproducible rate of approx. 2microliter/h per mg of protein. After accumulation in vitro, the three substances were released from the tissue into substrate-free medium at low rates. Sucrose present in the medium at concentrations up to 10 mg/ml was without effect on the accumulation of either [14C]sucrose or 125I-labelled poly(vinylpyrrolidone), but at higher concentrations inhibited the uptake of both substrates. Some batches of colloidal [198Au]gold had a significantly higher Endocytic Index (up to 5 microliter/h per mg of protein). The Endocytic Index of such a batch decreased with increasing substrate concentration, but colloidal gold did not decrease the Endocytic Index of 125I-labelled poly(vinylpyrrolidone). It is concluded that the three substrates enter the yolk sac by pinocytosis in the liquid phase. Those batches of colloidal [198Au]gold with higher Endocytic Indices are considered to enter also by adsorption on membrane binding-sites.

SUBMITTER: Roberts AV

PROVIDER: S-EPMC1183757 | biostudies-other | 1977 Nov

REPOSITORIES: biostudies-other

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Project description:BackgroundThe yolk sac (YS) is an extra-embryonic tissue that surrounds the yolk and absorbs, digests and transports nutrients during incubation of the avian embryo as well as during early term mammalian embryonic development. Understanding YS functions and development may enhance the efficient transfer of nutrients and optimize embryo development. To identify temporal large-scale patterns of gene expression and gain insights into processes and mechanisms in the YS, we performed a transcriptome study of the YS of chick embryos on embryonic days (E) E13, E15, E17, E19, and E21 (hatch).Results3547 genes exhibited a significantly changed expression across days. Clustering and functional annotation of these genes as well as histological sectioning of the YS revealed that we monitored two cell types: the epithelial cells and the erythropoietic cells of the YS. We observed a significant up-regulation of epithelial genes involved in lipid transport and metabolism between E13 and E19. YS epithelial cells expressed a vast array of lipoprotein receptors and fatty acid transporters. Several lysosomal genes (CTSA, PSAP, NPC2) and apolipoproteins genes (apoA1, A2, B, C3) were among the highest expressed, reflecting the intensive digestion and re-synthesis of lipoproteins in YS epithelial cells. Genes associated with cytoskeletal structure were down-regulated between E17 and E21 supporting histological evidence of a degradation of YS epithelial cells towards hatch. Expression patterns of hemoglobin synthesis genes indicated a high erythropoietic capacity of the YS between E13 and E15, which decreased towards hatch. YS histological sections confirmed these results. We also observed that YS epithelial cells expressed high levels of genes coding for plasma carrier proteins (ALB, AFP, LTF, TTR), normally produced by the liver.ConclusionsHere we expand current knowledge on developmental, nutritional and molecular processes in the YS. We demonstrate that in the final week of chick embryonic development, the YS plays different roles to support or replace the functions of several organs that have not yet reached their full functional capacity. The YS has a similar functional role as the intestine in digestion and transport of nutrients, the liver in producing plasma carrier proteins and coagulation factors, and the bone marrow in synthesis of blood cells.

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The pinocytosis of 125I-labelled poly(vinylpyrrolidone), [14C]sucrose and colloidal [198Au]gold by rat yolk sac cultured in vitro.

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