Rat thyroid lobes incubated with mannose-1 H, galactose-3H, or leucine-3 H, were studied by radioautography . With leucine-3 H and mannose-3H, the grain reaction observed in the light microscope is distributed diffusely over the cells at 5 min, with no reaction over the colloid . Later, the grains are concentrated towards the apex, and colloid reactions begin to appear by 2 hr . With galactose-1H, the reaction at 5 min is again restricted to the cells but it consists of clumped grains next to the nucleus . Soon after, grains are concentrated at the cell apex and colloid reactions appear in some follicles as early as 30 min . Puromycin almost totally inhibits incorporation of leucine 3H and mannose-3H, but has no detectable effect on galactose 3H incorporation during the 1 st hr . Quantitation of electron microscope radioautographs shows that mannose 3H label localizes initially in the rough endoplasmic reticulum, and by 1-2 hr much of this reaction is transferred to the Golgi apparatus . At 3 hr and subsequently, significant reactions are present over apical vesicles and colloid, while the Golgi reaction declines . Label associated with galactose 3H localizes initially in the Golgi apparatus and rapidly transfers to the apical vesicles, and then to the colloid . These findings indicate that mannose incorporation into thyroglobulin precursors occurs within the rough endoplasmic reticulum ; these precursors then migrate to the Golgi apparatus, where galactose incorporation takes place . The glycoprotein thus formed migrates via the apical vesicles to the colloid .

No abstract

The fact that the transfer of amphibians between black and white backgrounds causes the 'melanocyte-stimulating hormone (MSH) cells' of the pars intermedia of the pituitary to undergo considerable morphological change has been established for some time. The application of morphometric techniques to the 'MSH cells' of Xenopus has permitted the quantitative analysis of these changes at the ultrastructural level. Of the nine classes of organelle selected for analysis in these cells, three, namely nucleus, plasma membrane and dense bodies, showed no statistically significant changes. The remaining classes of organelle all showed significant changes in the percentage of the total cell volume that they occupied, although not all the organelles changed at the same rate. Transfer of animals from a white to a black background for up to 12 days was associated with increase in the percent volume of rough endoplasmic reticulum, Golgi membranes, Golgi granules and mitochondria and with a decrease in the percent volume of the fibrous granules. Return of animals to a white background after 6 days on a black background produced a reversal of the above changes with return to, or close to, white background (control) levels. This quantitative ultrastructural approach also highlights discrepancies in both the rate and magnitude of the changes in some of the organelles and related non-morphological parameters previously reported, e.g. the size of the rough endoplasmic reticulum and the rate of incorporation of labelled amino acid into protein; or the numbers of fibrous granules and the levels of detectable pituitary MSH. Some possible interpretations of these discrepancies are discussed.

No abstract

Summary.-A chromogenic substrate assay for the plasminogen activator (PA) activity of Lewis lung carcinoma cells has been developed. The cells were incubated with plasminogen, the activation of which to plasmin was measured by the amidolysis of the chromogenic substrate S-2251. This was routinely performed as a 4h serum-free assay, but a variation lasting 24h, in medium supplemented with plasminogen-free inhibitor-reduced serum, produced similar results. The assay also detected PA released into the medium. PA activity was proportional to cell density, and the assay was non-toxic to the cells.Assays were performed on cultures derived from primary and metastatic tumours. Host cells were effectively eliminated from such cultures but, because of an initial phase of tumour-cell death, PA assays were not carried out until cultures became established. No consistent difference was detected between PA levels in primary and metastatic cultures. However, these cultures were shown to be atypical of the parent tumour; they grew slowly when reinjected at the primary site, and their metastatic potential was impaired.