Specific banding patterns of human chromosomes

A 25-year odyssey of genomic technology advances and structural variant discovery

This perspective focuses on advances in genome technology over the last 25 years and their impact on germline variant discovery within the field of human genetics. The field has witnessed tremendous technological advances from microarrays to short-read sequencing and now long-read sequencing. Each technology has provided genome-wide access to different classes of human genetic variation. We are now on the verge of comprehensive variant detection of all forms of variation for the first time with a single assay. We predict that this transition will further transform our understanding of human health and biology and, more importantly, provide novel insights into the dynamic mutational processes shaping our genomes.

Identification of cryptic balanced translocations in couples with unexplained recurrent pregnancy loss based upon embryonic PGT-A results

PURPOSE

The goal of this study is to determine whether any balanced translocation (BT) had been missed by previous karyotyping in patients with unexplained recurrent pregnancy loss (uRPL).

METHODS

This case series included 48 uRPL-affected couples with normal karyotypes. The embryos from these couples have all undergone preimplantation testing for aneuploidies (PGT-A). Based on the PGT-A's results, 48 couples could be categorized into two groups: 17 couples whose multiple embryos were detected with similar structural variations (SVs, segmental/complete) and 31 couples without such findings but who did not develop any euploid embryo despite at least three high-quality blastocysts being tested. The peripheral blood sample of each partner was then collected for mate-pair sequencing (MPseq) to determine whether any of them were BT carriers.

RESULTS

MPseq analyses identified 13 BTs in the 17 couples whose multiple embryos had similar SVs detected (13/17, 76.47%) and three BTs in the 31 couples without euploid embryo obtained (3/31, 9.7%). Among the 16 MPseq-identified BTs, six were missed due to the limited resolution of G-banding karyotyping analysis, and the rest were mostly owing to the similar banding patterns and/or comparable sizes shared by the two segments exchanged.

CONCLUSION

A normal karyotype does not eliminate the possibility of carrying BT for couples with uRPL. The use of PGT-A allows us to perceive the "carrier couples" missed by karyotyping analysis, providing an increased risk of finding cryptic BTs if similar SVs are always detected on two chromosomes among multiple embryos. Nonetheless, certain carriers with translocated segments of sub-resolution may still go unnoticed.

The delineation of the Wolf-Hirschhorn syndrome over six decades: Illustration of the ongoing advances in phenotype analysis and cytogenomic technology

Since Hirschhorn's description in 1961, the history and chronology of the clinical, cytogenetic, and molecular characterization of Wolf-Hirschhorn syndrome (WHS) elegantly demonstrates the remarkable advances in genetic technology over the last six decades that have paralleled the delineation of the phenotype. After mention in the Human Chromosome Newsletter of a child with a visible deletion of the top of a B chromosome group, 4-5, Hirschhorn and colleagues companioned their report with that of Wolf et al. in Humangenetik in 1965, and the condition was recognized and named. The 1960-1970s witnessed the description of many of the now classic chromosome disorders, including WHS, while HRB allowed for the recognition of chromosome syndromes with smaller deletions/duplications. FISH probes, developed in the next two decades, enabled the characterization of the critical region of WHS and improved clinical diagnosis with subtelomeric probes. Cytogenomic microarray in the early-mid 2000s led to both improved diagnosis of WHS patients and documentation of microdeletions of <5 megabases, helping to characterize the critical regions for specific component phenotypes (e.g., seizures, face). Recently exome sequencing technology has led to the discovery of WHS patients with WHSC1 loss of function variants, displaying some cardinal features of the phenotype (face, growth, and developmental delay).

Mitotic chromosomes

Our understanding of the structure and function of mitotic chromosomes has come a long way since these iconic objects were first recognized more than 140 years ago, though many details remain to be elucidated. In this chapter, we start with the early history of chromosome studies and then describe the path that led to our current understanding of the formation and structure of mitotic chromosomes. We also discuss some of the remaining questions. It is now well established that each mitotic chromatid consists of a central organizing region containing a so-called "chromosome scaffold" from which loops of DNA project radially. Only a few key non-histone proteins and protein complexes are required to form the chromosome: topoisomerase IIα, cohesin, condensin I and condensin II, and the chromokinesin KIF4A. These proteins are concentrated along the axis of the chromatid. Condensins I and II are primarily responsible for shaping the chromosome and the scaffold, and they produce the loops of DNA by an ATP-dependent process known as loop extrusion. Modelling of Hi-C data suggests that condensin II adopts a spiral staircase arrangement with an extruded loop extending out from each step in a roughly helical pattern. Condensin I then forms loops nested within these larger condensin II loops, thereby giving rise to the final compaction of the mitotic chromosome in a process that requires Topo IIα.

Genomic Diagnosis for Pediatric Disorders: Revolution and Evolution

Powerful, recent advances in technologies to analyze the genome have had a profound impact on the practice of medical genetics, both in the laboratory and in the clinic. Increasing utilization of genome-wide testing such as chromosomal microarray analysis and exome sequencing have lead a shift toward a "genotype-first" approach. Numerous techniques are now available to diagnose a particular syndrome or phenotype, and while traditional techniques remain efficient tools in certain situations, higher-throughput technologies have become the de facto laboratory tool for diagnosis of most conditions. However, selecting the right assay or technology is challenging, and the wrong choice may lead to prolonged time to diagnosis, or even a missed diagnosis. In this review, we will discuss current core technologies for the diagnosis of classic genetic disorders to shed light on the benefits and disadvantages of these strategies, including diagnostic efficiency, variant interpretation, and secondary findings. Finally, we review upcoming technologies posed to impart further changes in the field of genetic diagnostics as we move toward "genome-first" practice.

Cellular and genomic approaches for exploring structural chromosomal rearrangements

Human chromosomes are arranged in a linear and conserved sequence order that undergoes further spatial folding within the three-dimensional space of the nucleus. Although structural variations in this organization are an important source of natural genetic diversity, cytogenetic aberrations can also underlie a number of human diseases and disorders. Approaches for studying chromosome structure began half a century ago with karyotyping of Giemsa-banded chromosomes and has now evolved to encompass high-resolution fluorescence microscopy, reporter-based assays, and next-generation DNA sequencing technologies. Here, we provide a general overview of experimental methods at different resolution and sensitivity scales and discuss how they can be complemented to provide synergistic insight into the study of human chromosome structural rearrangements. These approaches range from kilobase-level resolution DNA fluorescence in situ hybridization (FISH)-based imaging approaches of individual cells to genome-wide sequencing strategies that can capture nucleotide-level information from diverse sample types. Technological advances coupled to the combinatorial use of multiple methods have resulted in the discovery of new rearrangement classes along with mechanistic insights into the processes that drive structural alterations in the human genome.

Challenges in identifying large germline structural variants for clinical use by long read sequencing

Genomic structural variations, previously considered rare events, are widely recognized as a major source of inter-individual variability and hence, a major hurdle in optimum patient stratification and disease management. Herein, we focus on large complex germline structural variations and present challenges towards target treatment via the synergy of state-of-the-art approaches and information technology tools. A complex structural variation detection remains challenging, as there is no gold standard for identifying such genomic variations with long reads, especially when the chromosomal rearrangement in question is a few Mb in length. A clinical case with a large complex chromosomal rearrangement serves as a paradigm. We feel that functional validation and data interpretation are of outmost importance for information growth to be translated into knowledge growth and hence, new working practices are highlighted.

Generation of the induced human pluripotent stem cell lines CSSi009-A from a patient with a GNB5 pathogenic variant, and CSSi010-A from a CRISPR/Cas9 engineered GNB5 knock-out human cell line

GNB5 loss-of-function pathogenic variants cause IDDCA, a rare autosomal recessive human genetic disease characterized by infantile onset of intellectual disability, sinus bradycardia, hypotonia, visual abnormalities, and epilepsy. We generated human induced pluripotent stem cells (hiPSCs) from skin fibroblasts of a patient with the homozygous c.136delG frameshift variant, and a GNB5 knock-out (KO) line by CRISPR/Cas9 editing. hiPSCs express common pluripotency markers and differentiate into the three germ layers. These lines represent a powerful cellular model to study the molecular basis of GNB5-related disorders as well as offer an in vitro model for drug screening.

Angle-resolved light scattering of single human chromosomes: experiments and simulations

Angle-resolved light scattering measurements of human metaphase chromosomes were compared to the results of numerical light scattering simulations with geometrical models based on atomic force microscopy (AFM) measurements of the same chromosomes. The simulations were conducted using the discrete dipole approximation method (DDA), which solves Maxwell's equations for induced dipoles, positioned in a discrete lattice. A remarkable agreement between the light scattering simulations and measurements of all 6 studied chromosomes was found. Additionally, the influence of small changes in the orientation of a complex scatterer geometry on its angle-resolved scattering pattern is shown. A method is presented to approximate such variations in the scatterer's orientation by a linear shift of the angular scattering pattern. This method provides an initial guess on the scatterers orientation, reducing the amount of simulations needed considerably. It was validated on simulations of a cuboid and successfully applied in the evaluation of the chromosome measurements.

Traditional Prenatal Diagnosis: Past to Present

In the nearly 60 years since prenatal diagnosis for genetic disease was first offered, the field of prenatal diagnosis has progressed far past rudimentary uterine puncture to provide fetal material to assess gender and interpret risk. Concurrent with the improvements in invasive fetal sampling came technological advances in cytogenetics and molecular biology that widened both the scope of genetic disorders that could be diagnosed and also the resolution at which the human genome could be interrogated. Nowadays, routine blood work available to all pregnant women can determine the risk for common chromosome abnormalities; chorionic villus sampling (CVS) and amniocentesis can be used to diagnose nearly all conditions with a known genetic cause; and the genome and/or exome of a fetus with multiple anomalies can be sequenced in an attempt to determine the underlying etiology. This chapter will discuss some of the major advances in prenatal sampling and prenatal diagnostic laboratory techniques that have occurred over the past six decades.

Synthesis, convergence, and differences in the entangled histories of cytogenetics in medicine: A comparative study of Canada and Mexico

Most historians of science and medicine agree that medical interest in genetics intensified after 1930, and interest in the relationship of radiation damage and genetics continued and expanded after World War II. Moreover, they maintain that the synthesis and convergence of human genetics and cytological techniques in European centers resulted in their dissemination to centers in the United States, resulting in a new field of expertise focused on medicine and clinical research, known as cytogenetics. In this article, we broaden the scope of the inquiry by showing how the early histories of cytogenetics in Canada and Mexico unfolded against strikingly different backgrounds in clinical research and the delivery of health care. We thus argue that the field of cytogenetics did not emerge in a straightforward manner and develop in the same way in all countries. The article provides a brief background to the history of human cytogenetics, and then outlines key developments related to the early adoption of cytogenetics in Canada and Mexico. Conclusions are then drawn using comparisons of the different ways in which local determinants affected adoption. We then propose directions for future study focused on the ways in which circuits of practices, collaborative research, and transfers of knowledge have shaped how cytogenetics has come to be organised in medicine around the world.

Chk1 inhibition significantly potentiates activity of nucleoside analogs in TP53-mutated B-lymphoid cells

Treatment options for TP53-mutated lymphoid tumors are very limited. In experimental models, TP53-mutated lymphomas were sensitive to direct inhibition of checkpoint kinase 1 (Chk1), a pivotal regulator of replication. We initially tested the potential of the highly specific Chk1 inhibitor SCH900776 to synergize with nucleoside analogs (NAs) fludarabine, cytarabine and gemcitabine in cell lines derived from B-cell malignancies. In p53-proficient NALM-6 cells, SCH900776 added to NAs enhanced signaling towards Chk1 (pSer317/pSer345), effectively blocked Chk1 activation (Ser296 autophosphorylation), increased replication stress (p53 and γ-H2AX accumulation) and temporarily potentiated apoptosis. In p53-defective MEC-1 cell line representing adverse chronic lymphocytic leukemia (CLL), Chk1 inhibition together with NAs led to enhanced and sustained replication stress and significantly potentiated apoptosis. Altogether, among 17 tested cell lines SCH900776 sensitized four of them to all three NAs. Focusing further on MEC-1 and co-treatment of SCH900776 with fludarabine, we disclosed chromosome pulverization in cells undergoing aberrant mitoses. SCH900776 also increased the effect of fludarabine in a proportion of primary CLL samples treated with pro-proliferative stimuli, including those with TP53 disruption. Finally, we observed a fludarabine potentiation by SCH900776 in a T-cell leukemia 1 (TCL1)-driven mouse model of CLL. Collectively, we have substantiated the significant potential of Chk1 inhibition in B-lymphoid cells.

Characterization of human chromosomal material exchange with regard to the chromosome translocations using next-generation sequencing data

As an important subtype of structural variations, chromosomal translocation is associated with various diseases, especially cancers, by disrupting gene structures and functions. Traditional methods for identifying translocations are time consuming and have limited resolutions. Recently, a few studies have employed next-generation sequencing (NGS) technology for characterizing chromosomal translocations on human genome, obtaining high-throughput results with high resolutions. However, these studies are mainly focused on mechanism-specific or site-specific translocation mapping. In this study, we conducted a comprehensive genome-wide analysis on the characterization of human chromosomal material exchange with regard to the chromosome translocations. Using NGS data of 1,481 subjects from the 1000 Genomes Project, we identified 15,349,092 translocated DNA fragment pairs, ranging from 65 to 1,886 bp and with an average size of approximately 102 bp. On average, each individual genome carried about 10,364 pairs, covering approximately 0.069% of the genome. We identified 16 translocation hot regions, among which two regions did not contain repetitive fragments. Results of our study overlapped with a majority of previous results, containing approximately 79% of approximately 2,340 translocations characterized in three available translocation databases. In addition, our study identified five novel potential recurrent chromosomal material exchange regions with greater than 20% detection rates. Our results will be helpful for an accurate characterization of translocations in human genomes, and contribute as a resource for future studies of the roles of translocations in human disease etiology and mechanisms.

Cytogenetic in vivo assays in somatic cells

Chromosome aberration assays are employed to detect the induction of chromosome breakage (clastogenesis) in somatic and germ cells by direct observation of the chromosomal damage during metaphase analysis, or by indirect observation of chromosomal fragments. Thus, various types of cytogenetic change can be detected such as structural chromosome aberrations (CA), sister chromatid exchanges (SCE), ploidy changes, and micronuclei. Following the induction of the chromosomal damage, most of the aberrations and abnormalities detected by these assays can be detrimental or even lethal to the cell. Their presence, however, indicates a potential to also induce more subtle and therefore transmissible chromosomal damage which survives cell division to produce heritable cytogenetic changes. Usually, induced cytogenetic damage is accompanied by other genotoxic damage such as gene mutations.

Lymphocyte chromosomal aberration assay in radiation biodosimetry

Exposure to ionizing radiations, whether medical, occupational or accidental, leads to deleterious biological consequences like mortality or carcinogenesis. It is considered that no dose of ionizing radiation exposure is safe. However, once the accurate absorbed dose is estimated, one can be given appropriate medical care and the severe consequences can be minimized. Though several accurate physical dose estimation modalities exist, it is essential to estimate the absorbed dose in biological system taking into account the individual variation in radiation response, so as to plan suitable medical care. Over the last several decades, lots of efforts have been taken to design a rapid and easy biological dosimeter requiring minimum invasive procedures. The metaphase chromosomal aberration assay in human lymphocytes, though is labor intensive and requires skilled individuals, still remains the gold standard for radiation biodosimetry. The current review aims at discussing the human lymphocyte metaphase chromosomal aberration assay and recent developments involving the application of molecular cytogenetic approaches and other technological advancements to make the assay more authentic and simple to use even in the events of mass radiation casualties.

Nebulette is the second member of the nebulin family fused to the MLL gene in infant leukemia

Genetic aberrations involving the mixed lineage leukemia (MLL) gene are frequently diagnosed in infant acute lymphoblastic and acute myeloid leukemia. More than 60 fusion partner genes have been described at the molecular level, 31 of which have been characterized solely in infant leukemia cases. Here we describe a new MLL fusion partner gene, NEBL, which was identified in a case of acute myeloid leukemia in an infant. The chromosomal breakpoints of the MLL-NEBL and NEBL-MLL fusion genes were cloned by long-distance inverse polymerase chain reaction. The chromosomal breakpoints were located at 10p12, approximately 570 kb telomic of the MLLT10 (AF10) gene. AF10 and NEBL are localized in such close vicinity that they cannot be distinguished cytogenetically by G banding. Therefore, the combination of cytogenetic and independent molecular techniques such as long-distance inverse polymerase chain reaction are indispensable for the rapid identification and characterization of rare MLL rearrangements.

The hierarchically organized splitting of chromosomal bands for all human chromosomes

BACKGROUND

Chromosome banding is widely used in cytogenetics. However, the biological nature of hierarchically organized splitting of chromosomal bands of human chromosomes is an enigma and has not been, as yet, studied.

RESULTS

Here we present for the first time the hierarchically organized splitting of chromosomal bands in their sub-bands for all human chromosomes. To do this, array-proved multicolor banding (aMCB) probe-sets for all human chromosomes were applied to normal metaphase spreads of three different G-band levels. We confirmed for all chromosomes to be a general principle that only Giemsa-dark bands split into dark and light sub-bands, as we demonstrated previously by chromosome stretching. Thus, the biological band splitting is in > 50% of the sub-bands different than implemented by the ISCN nomenclature suggesting also a splitting of G-light bands. Locus-specific probes exemplary confirmed the results of MCB.

CONCLUSION

Overall, the present study enables a better understanding of chromosome architecture. The observed difference of biological and ISCN band-splitting may be an explanation why mapping data from human genome project do not always fit the cytogenetic mapping.

Guidelines for molecular karyotyping in constitutional genetic diagnosis

Array-based whole genome investigation or molecular karyotyping enables the genome-wide detection of submicroscopic imbalances. Proof-of-principle experiments have demonstrated that molecular karyotyping outperforms conventional karyotyping with regard to detection of chromosomal imbalances. This article identifies areas for which the technology seems matured and areas that require more investigations. Molecular karyotyping should be part of the genetic diagnostic work-up of patients with developmental disorders. For the implementation of the technique for other constitutional indications and in prenatal diagnosis, more research is appropriate. Also, the article aims to provide best practice guidelines for the application of array comparative genomic hybridisation to ensure both technical and clinical quality criteria that will optimise and standardise results and reports in diagnostic laboratories. In short, both the specificity and the sensitivity of the arrays should be evaluated in every laboratory offering the diagnostic test. Internal and external quality control programmes are urgently needed to evaluate and standardise the test results between laboratories.

Methodologies in cancer cytogenetics and molecular cytogenetics

Various types of cytogenetic and molecular cytogenetic approaches, including conventional banding, fluorescence in situ hybridization (FISH), fiber-FISH, comparative genomic hybridization (CGH), matrix array CGH, chromosome microdissection, and microcell-mediated chromosome transfer are summarized. The rationale, advantage, and limitations of each approach are discussed with respect to research and clinical applications in human neoplasia.

Chromosome banding techniques

Chromosome banding techniques produce a series of consistent landmarks along the length of metaphase chromosomes that allow for both recognition of individual chromosomes within a genome and identification of specific segments of individual chromosomes. These landmarks facilitate assessment of chromosome normalcy, identification of sites of chromosome breaks and alterations, and location of specific genes. This unit covers these basic banding techniques (Q-banding, G-banding, and R-banding), which produce virtually identical patterns of bands along the length of human chromosomes, although the bands and polymorphic regions highlighted may differ with each technique. These techniques highlight reproducible landmarks along the length of the chromosome and specialized staining techniques can be used to highlight particular regions of chromosomes, such as heterochromatic and repeated-sequence segments. These specialized techniques, nucleolar organizer region (NOR) staining, centromeric heterochromatin staining (C-banding), methylated satellite DNA staining (distamycin-DAPI banding), and replication banding are also presented in this unit.

Cultured human atherosclerotic plaque smooth muscle cells retain transforming potential and display enhanced expression of the myc protooncogene

The proliferation of vascular smooth muscle cells (SMC) is critical to atherosclerotic plaque formation. The monoclonal hypothesis proposes that the stimulus for this SMC proliferation is a mutational event. Here we describe a procedure for growing human plaque smooth muscle cells (p-SMC) in culture. We show that p-SMCs derived from two patients differ from SMC cultured from normal vascular tissue in expression of the protooncogene myc. One p-SMC strain was extensively characterized; these diploid, karyotypically normal cells have a finite life span in culture. Ultrastructural examination revealed two populations, one with classic contractile SMC appearance, the other, modulated to a synthetic state. Northern blotting showed a 2- to 6-fold and a 6- to 11-fold enhanced expression of myc by p-SMC, compared to SMC derived from healthy human aorta (HA-SMC) and saphenous vein (HV-SMC), respectively. In contrast, the p-SMC and HV-SMC expressed similar levels of message for the genes N-myc, L-myc, Ha-ras, fos, sis, myb, LDL receptor, EGF receptor, IGF I receptor, IGF II, and HMG CoA reductase. Finally, although p-SMCs are not tumorigenic, DNA isolated from these cells is positive in the transfection-nude mouse tumor assay. Myc, however, does not appear to be the transforming gene because no newly introduced human myc gene was detected in the p-SMC-associated nude mouse tumor. Thus human atherosclerotic p-SMCs possess both an activated myc gene and a transforming gene that is retained throughout many cell passages.

Chromosome preparation and high resolution banding techniques. A review

High resolution banding techniques enable detection of chromosome rearrangements even within major bands. Banded chromosomes prepared for light microscopic studies of intact metaphase plates are, however, highly modified structures compared with native chromosomes, and the high resolution banding techniques only seem possible because the following methods were standardized and combined. The use of colcemid, which prevents formation of the spindle and thereby collects cells at the metaphase-anaphase border, is routinely used for chromosome preparations. For high resolution banding studies, short exposure time and concentrations near the threshold value have been recommended by several authors. Several agents interfere with chromosome contraction processes, but only a few have had a lasting influence on high resolution banding studies. The most used agents are ethidium bromide, actinomycin D, and Hoechst 33258, which all partially inhibit chromosome contraction. Treatment with hypotonic solutions induces swelling of animal cells, and the methanol in the fixative denatures and precipitates protein by dehydration. The acetic acid coagulates nucleoproteins and causes swelling of the cells. The fixative penetrates the cells rapidly and preserves the chromosome structure. To obtain long segmented chromosomes suitable for high resolution banding hypotonic treatment with .075 M KCl, frequent changes of fixative and overnight fixation at 4 degrees C have been recommended. The use of cell synchronization, 5-bromodeoxyuridine incorporation into DNA, and fluorochrome-photolysis Giemsa (FPG)-staining have improved the quality of high resolution banding. Synchronization techniques, which select for lymphocyte populations in early divisions, provide excellent materials for chromosome preparations and induction of high resolution banding. The banding techniques seem to enhance differences already present in the chromosomes, and the differential Giemsa staining has recently been explained by interactions between the hydrophobic dye complex, the supercoiled DNA helix, and the denaturated histone core of the nucleosomes.

Reproduction in XYY males: two new cases and implications for genetic counseling

We present two children--one, 47,XY, + mar, and the other, 47,XY, + 21. Both fathers were found to have a 47,XYY chromosome constitution. The initial assumption was that the fathers' aneuploid conditions contributed to those of the offspring. However, the derivation of the marker chromosome could be paternal, maternal, or postzygotic, and examination of polymorphic structures of the number 21 chromosomes of the child with Down syndrome and his parents suggested maternal derivation of the supernumerary 21. To explore further the reproductive risks of an individual with the XYY constitution, previous reports of reproductive performance and testicular histology are examined as are two theories which suggest XYY males may be at an increased risk of producing aneuploid progeny. Based on these reports, recommendations are made for testing XYY males prior to genetic counseling.

A simple reproducible method for prometaphase chromosome analysis

A method is described for the analysis of chromosomes in prophase and early metaphase. It involves culturing the lymphocytes in medium RPMI-1640, supplemented with 10% autologous plasma instead of fetal bovine serum. Living cells are treated with actinomycin D and colcemid for 1 h prior to harvest and harvested early at 65 h of incubation, using a hypotonic solution formulated by Ohnuki (1968). The method has been tested on several hundred clinical samples on a routine basis. On average, 30% of the dividing cells were in prometaphase.

Chromosome banding and heterochromatin in Vicia faba

The distribution of bands in Vicia faba (broad bean) root-tip chromosomes as shown by acid treatment, quinacrine mustard fluorescence, SSC-Giemsa banding and orcein banding is documented. These bands coincide with the position of heterochromatin revealed by cold treatment. Heterochromatin in the large M chromosome is located in two areas: (a) around the centromere and (b) adjacent to the secondary constriction. Heterochromatin in the smaller, sub-telocentric S chromosomes is located in the intercalary and proximal areas of their long arms and in the short arm of two chromosomes. Most of the observed bands were not exclusive to one treatment but could be recognized in chromosomes prepared by several methods. The variable expression of particular chromosome segments with different banding techniques testifies to the existence of several classes of heterochromatin.

Classification of chromosomal eye syndromes

Human chromosome disease arises from a change in the number or structure of one or more chromosomes. The multiple genes represented in the duplicated or deleted chromosomes are not usually defective and any systemic abnormalities can be attributed to a change in gene dosage. Banding techniques are now commonly used to identify each chromosome and the specific chromosome duplication and deletion and structural rearrangements can now be identified unambiguously. Most ocular abnormalities have occurred in patients with chromosomal defects. Major ocular abnormalities, such as anophthalmia, cyclopia, retinoblastoma, microphthalmia, corneal opacities, coloboma, cataracts, intraocular cartilage, retinal dysplasia and absent optic nerves; and, minor abnormalities, such as ptosis, abnormal eyelid fissures, and Brushfield spots are present in individuals with abnormal chromosomes. The chromosome errors are usually present in all somatic tissues. consequently, multiple tissue abnormalities would be expected in most patients with chromosome abnormalities. Mental retardation is very common in those patients with abnormalities of autosomes. Therefore, it is unlikely that an isolated single clinical or histopathological ocular abnormality will be the result of a chromosome error. However, if the individual has multiple systemic abnormalities, then a chromosome error can be considered reasonably. Any chromosome disorder can be identified correctly by an appropriate banding chromosome determination on the affected individuals. With the possible exception of the association of 13q 14- and retinoblastoma, there does not appear to be any pathognomonic ocular abnormalities that occur in individuals with chromosome errors.

Isolation, culture and characterization of epithelial cells derived from rat ventral prostate

Epithelial-cell enriched primary cultures have been established from rat ventral prostate (RVP). Minced ventral prostates were dissociated with 0.5% collagenase in F12K tissue culture medium containing 1% fetal bovine serum. This treatment resulted in the gradual removal of stromal elements from the base of the epithelial cells. After 60 minutes of digestion the aggregates of epithelial cells were washed and plated at high density in F12K plus 10% horse serum. After 48 hours in vitro the unattached cells were removed from the culture dishes, washed, and reinoculated into new culture vessels containing fresh medium. After 96 hours in vitro, the aggregates had attached to the culture vessels and spread out to yield discrete patches of epithelial cells. By 144 hours in vitro the patches of cells had grown and coalesced to form a semi-confluent monolayer of epithelial cells. Ultrastructrual examination of these cultures indicated that adjacent cells were joined by desmosomes and tight junctions and had formed "lumen-like structures" into which projected microvilli. In addition, the cells contained secretory granules and tonofilaments, giving them a morphological appearance similar to prostate epithelial cells in the intact organ. The primary cultures also retained histochemical activities for acid phosphatase, beta-glucuronidase, and succinic dehydrogenase that were similar to the intact organ.