Enucleated L929 mouse fibroblasts support invasion and multiplication of Shigella flexneri 5a

Invasive bacteria can induce their own uptake and specify their intracellular localization; hence it is commonly assumed that proximate modulation of host cell transcription is not required for infection. However, bacteria can also modulate, directly or indirectly, the transcription of many host cell genes, whose role in the infection may be difficult to determine by global gene expression. Is the host cell nucleus proximately required for intracellular infection and, if so, for which pathogens and at what stages of infection? Enucleated cells were previously infected with Toxoplasma gondii, Chlamydia psittaci, C. trachomatis, or Rickettsia prowazekii. We enucleated L929 mouse fibroblasts by centrifugation in the presence of cytochalasin B, and compared the infection with Shigella flexneri M90T 5a of nucleated and enucleated cells. Percent infection and bacterial loads were estimated with a gentamicin suppression assay in cultures fixed and stained at different times after infection. Enucleation reduced by about half the percent of infected cells, a finding that may reflect the reduced endocytic ability of L929 cytoplasts. However, average numbers of bacteria and frequency distributions of bacterial numbers per cell at different times were similar in enucleated and nucleated cells. Bacteria with actin-rich tails were detected in both cytoplasts and nucleated cells. Lastly, cytoplasts were similarly infected 2 and 24 h after enucleation, suggesting that short-lived mRNAs were not involved in the infection. Productive S. flexneri infection could thus take place in cells unable to modulate gene transcription, RNA processing, or nucleus-dependent signaling cascades.

Intracellular distribution of vitamins B12 and vitamin B12 coenzyme (5,6 dimethylbenzimidazole cobamide) in normal and injured rat liver

Our study on the intracellular distribution of B12 and DBC on a normal and injured liver following the administration of these labelled test materials show that (1) with increasing interval, the pattern of distribution of these two closely related compounds in the various cellular fractions will simulate each other; (2) chromatography of B12 and DBC obtained from soluble fractions exhibited nearly identical Rf values; both findings lend support to our belief that the conversion of vitamin B12 to 5,6 dimethylbenzimidazole cobamide coenzyme took place; (3) in an injured liver, the initial uptake of either B12 or DBC activity is significantly different from the uptake, in almost all cellular fractions, of an intact liver; however, with prolonged interval, the pattern of distribution of B12 and DBC among the individual fractions will eventually be identical. (Summary)

Identification and localisation of resectable tumours in the liver.

With the currently available various imaging procedures, as small a tumor as 1 cm in diameter is detectable. However, such small tumors are detectable only in patients with cirrhosis who frequently develop hepatocellular carcinoma (HCC) in the Far East, by a regularly scheduled follow-up as generally practiced in Japan and Taiwan. The preoperative assessment of resectability and tolerable size of resection has improved with the modern liver function tests and imaging diagnosis. In this presentation, emphasis will be placed on the diagnosis of localization of a tumor within the liver rather than on the detection of tumors by imaging which has already been extensively documented.