Publisher Summary The nucleolus is organized at the nucleolus-organizing region of the chromosomes, which are generally visible as secondary constriction regions in metaphase chromosomes. The chromatin within the constriction region is lost at interphase inside the nucleolar mass. The chromatin is highly extended at this stage. At the ultrastructural level, the nucleolus has at least three components: (1) a granular component consisting mainly of ribonucleoproteins (RNP) granules—pars granulosa, (2) a fibrillar component, consisting of RNP fibrils—pars fibrosa, and (3) chromatin elements. Chromatin elements may be present in three forms: (1) nucleolus-associated chromatin, which most likely does not take part in nucleolus formation; however, the possibility of its association with condensed inactive ribosomal cistrons, at least in some cells, cannot be overruled at present, (2) septalike intranucleolar chromatin, and (3) isolated or dispersed intranucleolar chromatin threads. Intranucleolar chromatin is often associated with the pars fibrosa. Identical components can also be found in isolated nucleoli. Studies on the nucleoli in giant chromosomes indicate that the intranucleolar chromatin in these nucleoli is present as puffs of different sizes. The nucleolar chromatin is not an autonomous structure of the nucleolus but is a continuous structure and part of the nucleolar chromosome.

The nucleolar structure.

Lists are presented of references to all known publications describing cell properties that serve to characterize (i) known strains of HeLa and purported human cell lines indicated as HeLa contaminants, (ii) strains of human cell lines contaminated with human but non-HeLa cells, and (iii) strains of cells contaminated by cells from one or more other species. Frequencies of cell cross-contaminations are cited and references are presented to relatively simple techniques that could serve to detect such contamination.

https://science.sciencemag.org/content/sci/212/4493/446.full.pdf

Cross-contamination of cells in culture

A list is presented of references to all known publications on properties which have served to relate strains of HeLa cells to each other as well as to indict other purported human cell lines as HeLa cell contaminants. Eleven additional cell lines not previously indicted are described. When they exhibit (i) type A (fast) mobility for glucose-6-phosphate dehydrogenase, (ii) phosphoglucomutase type 1 at locus 1 and locus 3, (iii) absence of a Y chromosome by fluorescent staining, and (iv) possession of a complex of trypsin-Giemsa banded marker chromosomes present in known HeLa cells, then cell substrates regardless of designation should be considered de facto strains of HeLa.

https://science.sciencemag.org/content/sci/191/4222/96.full.pdf

HeLa cultures defined.

I . Introduction . . . . . . . . . . . . . I1 . Synchrony in naturally occurring multinucleate cells . . . . . . . A . Protozoa . . . . . . . . . . . . . . . B . Algae . . . . . . . . . . . . . . . C . Fungi . . . . . . . . . . . . . . . D . Invertebrate somatic tissues . . . . . . . . . . . E . Germ cell formation . . . . . . . . . . . . F . Fertilization and co-ordination of pronuclei G . Early embryonic development . . . . . . . . . . . H . Cell multiplication in viwo and in witro

Nucleo-cytoplasmic interactions in the achievement of nuclear synchrony in dna synthesis and mitosis in multinucleate cells

Sous l'effet de certains composes, le nucleole presente des lesions morphologiques distinctes et caracteristiques. Ces lesions consistent en une segregation des composants nucleolaires en trois zones: granulaire, fibrillaire et amorphe, avec parfois apparition d'une quatrieme zone, plus contrastee, de nature inconnue. Dans le but de determiner la specificite de la lesion et d'en etablir si possible la signification biochimique, des cellules d'embryons de rat sont traitees par differents antimetabolites agissant au niveau I) des precurseurs du DNA et du RNA, II) des polynucleotides, III) du systeme de transcription DNA-RNA et IV) de la synthese des proteines. Les substances qui donnent la segregation nucleolaire agissent toutes par liaison au DNA et action au niveau de la transcription du RNA (Groupe III). Ce sont: la Nogalamycine, la Daunomycine, l'Echinomycine, la Chromomycine A3, la Proflavine, le bromure d'ethidium, ainsi que l'Azaserine a fortes doses. La sequence de l'apparition des lesions de segregation causees par ces inhibiteurs metaboliques se retrouve de facon constante si on choisit bien les doses et le temps de traitement. L'action de ces inhibiteurs ainsi que leur mode de liaison au DNA sont etudies. Une hypothese de travail est proposee qui tient egalement compte de l'action nucleolaire selective deja connue de certaines substances, telles que l'Actinomycine D, la nitroquinoline N-oxyde, la Mitomycine et l'Aflatoxine.



The phenomenon of nucleolar segregation: Specific action of certain antimetabolites



Certain compounds produce selective and characteristic morphologic changes within the nucleolus. These lesions consist of a decrease in size and of a segregation and redistribution of the nucleolar components into three zones, granular, fibrillar and amorphous; occasionally, a contrasted fourth zone appears. With intent to determine the specificity of the lesion and to analyse its biochemical significance, rat embryonic cells were treated with various kinds of antimetabolites acting at the level of the I) Precursors of DNA and RNA, II) Polynucleotides, III) DNA-RNA template system and IV) Protein synthesis. Antimetabolites that induce nucleolar segregation are compounds that bind to DNA and interfere with its template activity for the conduct of DNA-directed RNA synthesis by RNA polymerase (Group III). They are: Nogalamycin, Daunomycin, Echinomycin, Chromomycin A3, Proflavine, ethidium bromide and also Azaserine at high concentrations. The sequential appearance of the lesions is constant if the concentrations and time of treatment are adequate. The action of those metabolic inhibitors and their mode of binding to DNA are reviewed. A working hypothesis is proposed, taking also in consideration the already known selective nucleolar action of compounds such as Actinomycin D, 4-nitroquinoline N-oxide, Mitomycin-C and Aflatoxin.

Fredy F. Strasser

Papers

Nucleic Acid Synthetic Patterns in Synchronized Mammalian Cells

Nucleolar and Cytoplasmic Ribonucleic Acid Inhibition by Excess Thymidine

Phase contrast time-lapse cinematography of cultivated normal and psoriatic adult human skin.