Relationship between illness-associated absence in day-care children and weather parameters.

This 5-year study demonstrated a statistically significant correlation between morbidity among children attending day-care centres and various weather parameters. The study was undertaken in south-central Sweden, where sharp seasonal contrasts in climatic and weather conditions occur. Illness-associated absence (IAA) decreased significantly when the weather was bright, sunny and warm, determined using average monthly weather parameters analysed over 60 months. This may be because good weather encourages outdoor activities which, in turn, reduce the risk of spreading respiratory tract infections as outdoor play areas are larger, body contact is less frequent, and any bacteria and viruses present will be readily dispersed. In multiple regression analysis, outdoor temperature was the most prominent parameter linked with IAA. This may reflect the behaviour of the staff with regard to various weather conditions. It is therefore to be recommended that children attending day-care centres should be allowed and encouraged to play outdoors when conditions allow.

Cell cycle progression in serum-free cultures of Sf9 insect cells: modulation by conditioned medium factors and implications for proliferation and productivity.

Cell cycle progression was studied in serum-free batch cultures of Spodoptera frugiperda (Sf9) insect cells, and the implications for proliferation and productivity were investigated. Cell cycle dynamics in KBM10 serum-free medium was characterized by an accumulation of 50-70% of the cells in the G(2)/M phase of the cell cycle during the first 24 h after inoculation. Following the cell cycle arrest, the cell population was redistributed into G(1) and in particular into the S phase. Maximum rate of proliferation (micro(N, max)) was reached 24-48 h after the release from cell cycle arrest, coinciding with a minimum distribution of cells in the G(2)/M phase. The following declining micro(N) could be explained by a slow increase in the G(2)/M cell population. However, at approximately 100 h, an abrupt increase in the amount of G(2)/M cells occurred. This switch occurred at about the same time point and cell density, irrespective of medium composition and maximum cell density. An octaploid population evolved from G(2)/M arrested cells, showing the occurrence of endoreplication in this cell line. In addition, conditioned medium factor(s) were found to increase micro(N,max), decrease the time to reach micro(N,max), and decrease the synchronization of cells in G(2)/M during the lag and growth phase. A conditioned medium factor appears to be a small peptide. On basis of these results we suggest that the observed cell cycle dynamics is the result of autoregulatory events occurring at key points during the course of a culture, and that entry into mitosis is the target for regulation. Infecting the Sf9 cells with recombinant baculovirus resulted in a linear increase in volumetric productivity of beta-galactosidase up to 68-75 h of culture. Beyond this point almost no product was formed. Medium renewal at the time of infection could only partly restore the lost hypertrophy and product yield of cultures infected after the transition point. The critical time of infection correlated to the time when the mean population cell volume had attained a minimum, and this occurred 24 h before the switch into the G(2)/M phase. We suggest that the cell density dependent decrease in productivity ultimately depends on the autoregulatory events leading to G(2)/M cell cycle arrest.

Absence due to illness among toddlers in day-care centres in relation to child group structure.

The present work demonstrates a close association between illness-associated absence among children below 4 y of age in day-care, and the age-related composition of the child groups. The study, which spanned a 4 y period and is based on illness-related absence from day-care in a Stockholm suburb, shows that morbidity decreases significantly among young children as age-integration in the groups is intensified. Absence due to illness was most common in toddler groups of infants up to 3 y of age. Among sibling groups of children in the age range 0-6 y, illness-related absence was lower among toddlers compared to toddlers in age-separated groups, and significantly lower in extended sibling groups in the age range 0-12 y. Morbidity among children older than 3 y was not affected in the same way by group structure.

Exponential growth, random transitions and progress through the G1 phase: computer simulation of experimental data.

At a time of increasing knowledge of gene and molecular regulation of cell cycle progression, a re-evaluation is presented concerning a phenomenon discussed before the present expanding era of cell cycle research. 'Random transition' and exponential slopes of alpha- and beta-curves were conceived in the 1970s and early 1980s to explain cell cycle progression. An exponential behaviour of the beta-curve was claimed as being necessary and sufficient for a 'random transition' in the cell cycle. In our present work, similar slopes of those curves were shown to materialize when the increase in mass of single cells was set as exponential in a structured cell cycle model where DNA replication and increase in cell mass were postulated to be two loosely coupled subcycles of the cell cycle, without introducing any 'random transition'. Findings published in the 1980s demonstrating the effect of serum depletion of 3T3 Balb-c cells were simulated and the shallower slope of the alpha- and beta-curves found experimentally could be attributed to the reduced rate of exponential growth in cell mass, rather than to a reduced 'transition probability'.

Cell cycle progression: computer simulation of uncoupled subcycles of DNA replication and cell growth.

A computer simulation is presented for cell proliferation in a structured cell cycle model. The simulation takes into account the idea that DNA replication and cell growth are two loosely coupled subcycles. The simulation experiments performed offer an explanation for the close correlation often found in interdivision times of sister cell pairs and demonstrate that the exponential slope of the so-called beta-curve is linked to an exponential increase in cell mass. However, in synchronization experiments, a linear increase in mean mass of a cell population develops over time. A channel is opened for a genetic and growth rate influence extending from grandparent to granddaughter. Positive and negative time correlations close to zero still occurred for mother-daughter cell cycles. The computer program leaves two sites in the cell cycle available for gene, molecular and size checkpoints, one in G1 and one in G2. The simulation experiments bridge the gap between models considering (i) size control, (ii) transition probability, and (iii) inherited properties as interpretations of cell cycle progression and are applicable to embryonic cells with the potential to differentiate, somatic cells, and to the kinetics of activation of serum-starved cells. A G0 state is also defined.

The child group used as a reference system when analysing frequency of morbidity in day-care centres.

Morbidity frequency was analysed among children attending six day-care centres in a suburb of Stockholm, Sweden. Absence due to illness was calculated annually for each child and correlated with each child's own group. Thus a child was classified as "often sick" or "mainly healthy" in relation to the other children in the child's own group, constituting a reference system. In almost every group a "sick third" was found, whose absence due to illness was twice that of the rest of the group. Children from families of lower social standing, those with a relatively large number of siblings and those living in poor social conditions were found to be among those most often reported as sick. In such families, smoking was more commonplace. These parents more often lived in a rented apartment than in a single detached owner house. Multiple linear regression analysis revealed that young mothers and children with several siblings had the strongest correlation with absence due to illness of the proband child. Increasing maternal age revealed improvement vis-à-vis all socioeconomic parameters investigated, reflecting an improvement in standing correlated to less sick children.

Polyploidization by means of endoduplication in a human breast cancer cell line.

Near DNA diploid human adult solid tumors are often associated with certain near-tetraploid cells. In an established human breast cancer cell line, Hs578T, with a DNA index in the hyperdiploid region, polyploid cells appeared during exponential growth. Among clones generated from single cells and analyzed by the video time lapse technique, an intraclonal interdivision time (IDT) heterogeneity is presented that renders endoduplication a plausible explanation for the generation of the polyploid cells observed. This conclusion, drawn from our IDT analysis, is supported by curves drawn from counting grain-positive cells during continuous labeling with [3H]-thymidine. Our results are compared with a parallel analysis of the aneuploid human breast cancer cell line MDA-231, generating intraclonal IDT heterogeneity, due mainly to the mitotic instability of that line, as we reported previously.

Partition of protein and DNA during cytokinesis in human breast cancer cell lines.

Three human breast cancer cell lines (HTB-126, MDA-231, and HTB-122) with DNA index (DI) values between 1.26 and 1.72 were analysed together with a diploid mouse embryonal carcinoma cell line (PCC3) by a TV-video time-lapse technique (pedigree analysis). Cytochemical parameters (DNA and proteins) were studied in individual cells in a rapid scanning microspectrophotometer. Post-mitotic sister cell pairs were analysed after Feulgen-naphthol-yellow staining. The DI values of the cell lines were selected to reflect various well-known clinical ploidy entities differing in malignancy potentials. A mitotic disturbance of the partition of DNA and protein to daughter cells was found in particular in MDA-231 closest to the triploid DNA modal value (DI = 1.37). Duration of mitosis was considerably longer in the near triploid line compared to the other lines. The MDA-231 line was also least sensitive to suboptimal growth conditions. This report calls attention to a possible causality between mitotic error and intraclonal genotype and cell mass heterogeneity.

DNA and nuclear protein characteristics in non-neoplastic and neoplastic endometrial tissue.

Feulgen-DNA and nuclear protein (NP) measurements were performed on non-neoplastic and neoplastic endometrium. Non-neoplastic endometrial cells were exclusively characterized by euploid nuclear DNA content. The NP content may vary significantly in relation to the proliferative stage as reflected by a 2-3-fold increase NP/DNA ratio in growing as compared to growth arrested cells. Endometrial adenocarcinomas could be subdivided into euploid and aneuploid types. The euploid tumors were found to exhibit DNA and NP characteristics comparable with those of normal tissue. In contrast, aneuploid tumors showed DNA and NP characteristics indicating increased proliferative activity as well as a pronounced disorder between the DNA and protein cycle.

Dissociation of cellular protein and DNA content in mild and moderate dysplasia as a reflection of the degree of aneuploidy in cancer.

Tumor progression was analyzed in vivo. The bronchial epithelium in five beagle dogs was weekly treated by 20-methylcholanthrene (20-MC). Bronchial cells were harvested before each application of the drug. The cytologic criteria used in the diagnostic procedure were based on a grading developed for Papanicolaou-stained preparations of human squamous bronchial epithelium. The cells were then destained and restained by Feulgen-naphthol yellow S technique. An increased variation in the protein/DNA ratio was an early event in tumorigenesis; it occurred even before aneuploid cells appeared in mild dysplasia, as compared with the control cells. A large increase in the coefficient of variation (CV) in the protein/DNA ratio in mild dysplasia vis-a-vis the control cells was positively correlated to the degree of aneuploidy occurring later in tumorigenesis. These results were compared with the findings in breast cancer cells from patients with near-diploid, aneuploid and near-tetraploid tumors. The CV in the protein/DNA ratio was significantly higher in the aneuploid tumors, indicating an increased dissociation between cell growth and DNA synthesis.

Partition of protein (mass) to sister cell pairs at mitosis: a re-evaluation.

Since the 1960s it has been thought that there is to some extent a difference in the partition of mass to daughter cells at mitosis. Recent studies using modern techniques give further support to such a phenomenon, which has become almost an axiom in cell biology. It has been suggested that such unequal distribution of metabolic constituents at mitosis contributes to the dispersion in cell generation times. In the present work, PCC3 embryonal carcinoma (EC) cells were studied as undifferentiated G1 sister pairs by microspectrophotometry (MSP) following Feulgen-Naphthol Yellow staining (FNYS), in order to evaluate their protein content. Despite the considerable intraclonal intermitotic time heterogeneity found in undifferentiated PCC3 EC cells, it was concluded thta the postmitotic difference in mass (protein) between sister cell pairs exerts a minimal influence upon the cell population mass variability, whereas it was deduced to have an influence upon variation in interphase time duration when comparing sister cell pairs. This offers a cell-physiological explanation to the randomly distributed difference repeatedly found between sister cell generation times. Furthermore, there was no correlation seen between the mass difference found between sister cell pairs postmitotically and the size of the mother cell.

Evidence for an intraclonal random shift between two types of cell cycle times in an embryonal carcinoma cell line.

In a recent paper we reported the discovery of an intraclonal bimodal-like cell cycle time variation within the multipotent embryonal carcinoma (EC) PCC3 N/1 line growing in the exponential phase in the undifferentiated state. The variability was found to be localized in the G1 period. Furthermore, an inverse relation between cell size and cell generation time was found in the cell system analysed. It was suggested that the bimodal-like intraclonal time variability previously reported was attributable to an intraclonal shift between two types of cell-growth-rate cycles and that the cell-growth cycle has a supramitotic character, being dissociated from the DNA-division cycle. The growth rate heterogeneity in the cell population was found to need three cell cycles to reach full dispersion in time. This was assumed to be due to a decreased inheritance from sister cell pairs to second cousin cell pairs. Thus, the interesting feature is that in one and the same multipotent cell line there was evidence for an intraclonal instability with a random shift between two types of cell cycle differing in the duration of their G1 period.

Growth rate regulation and random transition. A study performed on embryonal carcinoma cell lines. I.

Analyses of cell-cycle characteristics of the three embryonal carcinoma (EC) cell lines F9, PCC3 N/1 and PCC4 Azal, have been performed. The three lines reflect successive stages in early mouse embryogenesis as regards cell surface antigens and cell-cycle characteristics. In an attempt to understand changes in cell-cycle characteristics occurring during early embryogenesis, the two-random transition probability (TP) model was applied to the EC-cell system--and particularly to the F9 line. By utilizing an intraclonal heterogeneity in intermitotic times found in these EC lines, a growth-regulating point was introduced as a modification of the two-random TP model. The modified model was found to be very useful when demonstrating the cell-cycle growth kinetics of the F9 line. The model is used in an accompanying paper to extend the analysis of cell-cycle characteristics in undifferentiated EC cells.

Cell growth and cell division: dissociated and random initiated? A study performed on embryonal carcinoma cell lines. II.

The 'random transition probability' cell-cycle models have so far failed to convincingly link the transition events with phenomena describable by biochemical methods. The study presented was carried out on the F9 and PCC3 N/1 embryonal carcinoma (EC) cell lines. We now report an extended analysis of the two-random transition probability (TP) model and preliminary results are presented showing that the deterministic L period in that model can be regarded as reflecting the 'cell-growth cycle'. Evidence is presented that suggests that the 'cell-growth cycle' is a supramitotic deterministic phase--i.e. starting in one cell cycle and being completed in the next following G1 period and dissociated from the 'DNA-division cycle'. This phenomenon makes an interesting contribution to the old knowledge of a stepwise G1 prolongation during early embryogenesis in yielding a mechanism by which the cell can alter the ratio of nucleus to cytoplasm prior to the onset of gene expression.

A comparative study of the cell cycles of nullipotent and multipotent embryonal carcinoma cell lines during exponential growth.

Three embryonal carcinoma (EC) cell lines F9, PCC4 Azal, and PCC3 N/1 with a common origin from the transplantable ascites teratoma OTT6050 were analyzed with regard to cell cycle characteristics during exponential growth in the undifferentiated state. The three lines, in the sequence mentioned, have been shown to represent successive stages in early normal mouse embryogenesis from morula to blastocyst, as reflected in their cell surface antigens. In the multipotent lines an increased intraclonal variability in intermitotic times was found when analyzing family trees. In the PCC3 N/1 line the distribution was almost bimodal. The increased intermitotic time variability was found to be represented in the G1 period that varied from less than 1 hr up to about 6 hr in the PCC3 N/1 line, with a mean value of 3.4 hr. The G1 period of the F9 line had a range of only 3.5 hr, with a mean value of 1.5 hr. The S-G2 period was found to be very similar in length in all three lines.

Morphology of live seminal and postcoital cervical spermatozoa and its bearing on human fertility.

Various seminal variables were studied in two groups of infertile couples and in one fertile control group. Sperm morphology was emphasized. Patients with normal postcoital tests and sperm counts exceeding 5 mill/ml were selected and followed prospectively. The two clinical groups could then be identified: a. couples who were persistently infertile during the 3 years of observation and whose infertility was not explained by the clinical investigation, and; b. couples where conception was achieved during the period of observation, either spontaneously or after treatment of the woman. In the latter group all the variables of semen analysis were identical with those of the control group. Differences between the two groups of infertile patients were noted only with respect to the morphology of live spermatozoa of the semen sample and of postcoital spermatozoa within the cervical secretion. It is concluded that these two variables of sperm evaluation are of prognostic significance with regard to future fertility.