Lysosomal enzyme activities in different types of amniotic fluid cells measured by microchemical methods, combined with interference microscopy

Quantitative cytochemical analysis of (single) cultured cells

Human fibroblasts or amniotic fluid cells can be cultivated in special dishes with a bottom of thin transparent plastic foil. After quick freezing and freeze-drying small groups of cultured cells or single cells can be isolated by dissecting small pieces of plastic foil under the stereomicroscope. These can be incubated in (sub)microlitre volumes of substrate and the absorbance, fluorescence or radioactivity can be measured and expressed per cell. When absorbance is measured with a microscope spectrophotometer in 1-10 microliter, microcuvettes, the minimum amount of coloured product that can be determined is of the order of 10(-11) moles. Incubation under paraffin oil in 0.05 microliter of substrate, followed by fluorescence measurements in 1-5 microliter with a microscope fluorometer, allows down to 10(-14) mol of methylumbelliferone, which is the end-product in many analyses of lysosomal enzymes, to be detected. (Re)cycling procedures have an even greater sensitivity (10(-15)-10(-19)mol) but they are more complicated and limited to NAD(P)(H)-dependent reactions. Several radiometric procedures have also been adapted for the analysis of small numbers of cultured cells but most of them still require 10(4)-10(5) human fibroblasts. These microtechniques allow rapid prenatal diagnosis of at least 20 different genetic metabolic diseases to be made within 7-14 days after amniocentesis at the 14th-16th week of pregnancy. Enzyme assays on single cultured cells have also enabled complementation studies to be done on heterokaryons after hybridization of different types of mutant fibroblasts, as well as investigations of the intercellular exchange of lysosomal enzymes between normal and mutant cells.

Studies on the origin of human amniotic fluid cells by immunofluorescent staining of keratin filaments

Cultivated cells obtained by amniocentesis for antenatal diagnosis were examined for the presence of keratin filaments by immunofluorescent staining techniques. In primary cultures, cells in fibroblast type colonies do not possess keratin filaments whereas cells in epithelial type colonies show positive staining of keratin fibres. The majority of cells in amniotic fluid type colonies also stain positively with antikeratin antibody. After the primary cells have been subcultured, most of them appear fibroblastic yet stain positively with antikeratin antibody. The patterns formed by these stained fibres resemble those seen in primary cultures of amniotic fluid type cells. These results indicate that the amniotic fluid type cells (which predominate in primary cultures) and the majority of cells in subcultures (routinely used for antenatal diagnosis of genetic metabolic disorders) are epithelial in origin.

Separation of amniotic fluid cell types in primary culture by Percoll density gradient centrifugation

Amniotic fluid cells obtained by transabdominal amniocentesis at 15-17 weeks of gestation and cultured for 15 and 21 days were separated into three fractions by density gradient centrifugation in Percoll. Each fraction (or peak) corresponded to the following densities: peak A, 1.02-1.03 g/ml; peak B, 1.04-1.05; peak C, 1.05-1.06. Peak A was composed of both non-viable and viable cells; the latter adopted the morphology of epithelial cells in culture. Peak B contained a mixture of fibroblasts and epithelioid cells and peak C had only epithelioid cells. The variability of N-acetyl-beta-hexosaminidase and alkaline phosphatase activities was reduced in peaks B and C as compared to that of peak A and of unseparated cells suggesting that more defined and homogeneous cell types for enzymatic determinations can be obtained by centrifugation in Percoll density gradient. In prenatal diagnosis of biochemical defects, the separation of cells would permit a more precise diagnosis by eliminating enzyme variability due to the presence of different cell types or non-viable cells.

Cell genetic studies on propionyl-CoA carboxylase deficient cell lines

Thirteen propionyl-CoA carboxylase (PCC)-deficient fibroblast lines were analysed for complementation by examining the incorporation of [14C]propionate into trichloroacetic-acid insoluble cellular macromolecules of polyethylene-glycol-dimethyl-sulphoxide induced heterokaryons formed by fusion of mutant cell lines. Corrections for variations in the rate of protein synthesis of the heterokaryons and individual cell lines was made by measuring the incorporation of [3H]lysine, added simultaneously with the labelled propionate. Two distinct complementation groups were found in this sample of PCC-deficient cell lines. Evidence for intragenic complementation was not obtained.

Chromosome analyses and anchorage-independent growth of SV40-induced morphologically transformed epithelial cells from amniotic fluids

Epithelial cells from amniotic fluid cell cultures are morphologically transformed by simian virus 40, 20 to 30 d after infection. The cells of the transformed colonies are highly basophilic, have a high nuclear-to-cytoplasmic ratio, and show a dense growth pattern. The cells are virus producers, and ultimately, after continuous passage, the cell lines reach a crisis situation with no growth. Twelve morphologically transformed cell colonies were isolated from five different individuals for chromosome analyses after approximately 18 population doublings (second bottle passage). For all cell lines diploid cells were observed. Banding of the chromosomes revealed normal morphology of euchromatic and heterochromatic regions. The suggestion is made that chromosome alteration is not necessary, nor a prerequisite, for the morphologically transformed phenotype to be expressed and that the transformation process per se causes chromosomal instability. Tests for colony formation of the 12 cell lines in semisolid medium showed that different transformed colony isolates from the same individual donor of the cells either formed or did not form colonies in agar. The size of the colonies was also consistent within individuals as compared to between individuals. These limited results are suggestive of a dependence upon the genetic constitution of the individual donor of the cells for colony formation in soft agar.

Enhancement of human amniotic cell growth by Ficoll-Paque gradient fractionation

Ficoll-Paque isopycnic centrifugation was used as a preparative procedure for amniotic fluid (AF) cells prior to tissue culture. This technique serves to reduce contaminating erythrocytes and also enhances cell growth or mitotic indices. The technique described in this report yields three subfractions designated as a turbid interphase layer (F-2), a middle cell layer (F-3), and a bottom pellet (F-4). The middle cell layer (F-3) demonstrated better cell growth and higher mitotic index than any of the other fractions or control unfractionated amniotic fluid cells. The use of Ficoll-Paque isopycnic preparative centrifugation of amniotic fluid cells is a valuable adjunct in cell culture for cytogenetic analysis. This may be especially true when amniotic fluid contains large numbers of erythrocytes.

Microenzymatic assays for lysosomal enzymes in primary amniotic fluid cell cultures

A study of three lysosomal enzymes (hexosaminidase, beta-galactosidase and alpha-galactosidase) in normal primary amniotic fluid cell cultures using a microenzymatic assay is presented. No difference in enzyme activity was found between primary and amniotic cell cultures in passage number one. A progressive change in the proportions of hexosaminidase A and hexosaminidase B with time was demonstrated in culture. The feasibility of this procedure for the early prenatal diagnosis of disorders due to lysosomal enzyme deficiency is discussed.

Prenatal diagnosis of xeroderma pigmentosum (group C) using assays of unscheduled DNA synthesis and postreplication repair

The analysis of DNA repair processes is described in two pregnancies at risk for xeroderma pigmentosum. In both cases, excision repair (measured by unscheduled DNA synthesis) and postreplication repair were analyzed. An affected and an unaffected fetus were identified within 3 weeks after amniocentesis. The cells from the affected fetus were found to be deficient in excision DNA repair, whereas the PRR patterns were intermediate between those of normal and PRR deficient cells. This indicates the possibility of prenatal diagnosis of PRR deficient XP patients (XP variants).

A scanning microinterferometer with correction of errors caused by overlapping 'ghost' images

An experimental setup has been built to correct the errors caused by overlapping 'ghost' images when scanning and integrating measurements are carried out with the Jamin-Libedef interference microscope. First a reference field with the object, producing the 'ghost' image, is scanned and the values of the optical path difference (OPD) of each point in the reference field are stored in a computer. Subsequently, the OPD of the object to be measured is calculated for each point by adding the measuring result to the average OPD of five points, located around the corresponding point in the reference field. The applicability of the setup has been tested by measurements with Sepharose beads, Hela cells and the Zeiss microinterference refractometer. The difference between measurements on the same object with and without overlapping 'ghost' image was about 10%. The reproducibility was tested by repeated measurements on the same cell whereby a standard deviation of 1.1% was found.