Prenatal diagnosis of trisomy 13 on fetal cells obtained from maternal blood after minor enrichment.

In a pilot study to establish fetal nucleated red blood cell (NRBC) detection in maternal blood, trisomy 13 was diagnosed by FISH analysis at 11 weeks' gestation. The NRBCs were detected after a single-step ficoll density gradient enrichment. In blood samples taken both before and after CVS, 52 and 80 NRBCs, respectively, were found to be positive for fetal haemoglobin. In 47 per cent of these cells, FISH analysis for X and Y chromosomes confirmed the fetal sex. Moreover, 48 per cent of these NRBCs showed three fluorescent signals for a chromosome 13 probe, which confirmed the diagnosis of trisomy 13, previously detected at CVS karyotyping. This is the first report of non-invasive prenatal diagnosis of trisomy 13, i.e., pre-CVS, in the first trimester. The high number of fetal NRBCs detected indicates a connection with aneuploidy, probably due to early impairment of the feto-maternal barrier.

Development of a preparation and staining method for fetal erythroblasts in maternal blood: simultaneous immunocytochemical staining and FISH analysis.

In order to detect fetal nucleated red blood cells (NRBCs) in maternal blood, a protocol was developed which aimed at producing a reliable staining method for combined immunocytochemical and FISH analysis. The technique had to be suitable for eventual automated screening of slides. Chorionic villi washings, cord blood, and maternal blood samples were used for this study. After a density gradient separation and centrifugal cytology, slides were stained either with 3,3-diaminobenzidin (DAB), a marker for heme, or with antibodies against the gamma-chain of fetal hemoglobin (HbF). FISH analysis for both X- and Y-chromosomes was performed on the same slides. Cytocentrifugation provided a controlled cell density on the slides with good cell morphology. Both the DAB and HbF staining were suitable for manual screening of large numbers of slides. The HbF staining, although supposed to be more specific for fetal NRBCs, appeared to be more sensitive to minor changes in preparation. We were eventually able to combine HbF staining with FISH analysis, and produced a detection efficiency of >85% for both X- and Y-chromosome signals. This preparation protocol simplifies the detection of NRBCs in maternal blood. Immunocytochemical staining and FISH analysis can be performed on the same cell with good image contrast, thus facilitating both manual and automated image analysis. This will facilitate the use of this approach for prenatal diagnosis.

Fetal cell detection in maternal blood: a study in 236 samples using erythroblast morphology, DAB and HbF staining, and FISH analysis.

A protocol to detect fetal nucleated red blood cells (NRBCs) was tested in 217 pregnant women and in 19 nonpregnant controls. All the pregnant women were sampled after chorionic villus sampling (CVS); 20 were also sampled pre-CVS. NRBC recognition was based upon morphology by using staining of hemoglobin with 3,3-diaminobenzidin (DAB) or by immunocytochemical staining for fetal hemoglobin (HbF). This was combined with FISH analysis for both the X- and Y-chromosomes on the same cells. Progressive refinement of the methods increased the number of cases where NRBCs were detected from 53% (DAB) to 75% and 78% for DAB and HbF staining, respectively, with on average 43 NRBCs (range, 1-220). DAB gave a slightly higher yield than HbF in the lower cell count range (<25). In 6 out of 18 controls, NRBCs were detected with DAB, vs. 1 out of 19 (5%) with HbF. FISH analysis in 41 cases resulted in correct sex prediction in 80% (DAB) and 89% (HbF), respectively. Our data demonstrated an increase of cases with NRBCs (30% to 75%), as well as a rise of the mean number of NRBCs (6 to 29 cells), after CVS. We conclude that DAB staining is a straightforward way to screen for the presence of NRBCs in maternal blood, but is not specific for NRBCs of fetal origin. HbF immunophenotyping is a reliable marker for fetal NRBCs, which detected slightly fewer NRBCs than DAB-staining, but improved sex prediction and significantly reduced false-positive results. CVS at 10-13 weeks of gestation causes a significant increase of NRBCs in maternal blood. These data indicate that further refinement of NRBC detection is needed before application of noninvasive prenatal diagnosis using maternal blood is feasible.

Saponin pre-treatment in pre-embedding electron microscopic in situ hybridization for detection of specific RNA sequences in cultured cells: a methodological study.

We describe a method for detection of specific RNA targets in cultured cells at the electron microscopic (EM) level using pre-embedding in situ hybridization (ISH). The specimens were monitored by reflection-contrast microscopy (RCM) before processing for EM. A good balance between preservation of ultrastructure and intensity of hybridization signals was obtained by using mild aldehyde fixation followed by saponin permeabilization. Digoxigenin-labeled probes were used for detection of human elongation factor (HEF) mRNA in HeLa cells, immediate early (IE) mRNA in rat 9G cells, and 28S rRNA in both cell lines. The hybrids were detected immunocytochemically by the peroxidase/diaminobenzidine (DAB) method or by ultra-small gold with silver enhancement. Comparison of these methods favored the peroxidase/DAB system. The accessibility of RNA in the different cell compartments was dependent on the extent of cross-linking during primary fixation even after permeabilization with saponin. By using the most optimal ISH protocol and the peroxidase/DAB system, we detected 28S rRNA over all ribosomes in the cytoplasm but not in the nucleoli, and IE mRNA in a large spot with many smaller spots around it in the nucleoplasm as well as in speckles over the cytoplasm. The sensitivity of the method is such that HEF housekeeping gene transcripts were detected in the cytoplasm.

Monitoring morphology and signal during non-radioactive in situ hybridization procedures by reflection-contrast microscopy and transmission electron microscopy.

We analyzed the effects of steps in RNA in situ hybridization (ISH) procedures on morphology and hybridization signal with reflection-contrast microscopy (RCM) and transmission electron microscopy (TEM). In chessboard experiments, a range of fixatives containing formaldehyde, glutaraldehyde, or both, and various permeabilization protocols, including ethanol and pepsin treatment, were investigated. A transfected rat fibroblast cell line that harbors an inducible human cytomegalovirus immediate early (IE) transcription unit, and specific probes for 28S ribosomal RNA and IE messenger RNA were used for this purpose. Probes were labeled with digoxigenin and hybrids were detected with anti-digoxigenin F(ab)2 fragments conjugated to horseradish peroxidase, followed by diaminobenzidine/H2O2 reaction. Effects of fixation and pre-treatments on RNA detection efficiency and morphology were monitored by RCM on whole cells. After Epon embedding and ultra-thin cross-sectioning, the corresponding TEM images were obtained. With the pre-treatments analyzed, it appeared impossible to find an acceptable balance between ISH signals and preservation of ultrastructural morphology: when good signal-to-noise ratios are obtained, the ultrastructural morphology is already deteriorated. We discuss the parameters that influence the fragile balance between high RNA detection efficiency and good preservation of ultrastructure and the benefit of RCM monitoring in the development and procedures for pre-embedding electron microscopic ISH.