The applicability of interphase chromosome-specific multicolor banding (ICS-MCB) for studying

Background : Interphase chromosome-specific multicolor banding (ICS-MCB) has been developed for studying whole chromosomes in interphase nuclei at any stage of the cell cycle at molecular resolution. Previously, important biomedical discoveries have been made using the technique. In the postgenomic era, a need appears to exist for a reevaluation of molecular cytogenetic techniques, including ICS-MCB, which seems to take a well-deserved place. Aim of the study : The aim of the present study is to address the applicability of ICS-MCB for studying neurodevelopmental and neurodegenerative disorders. Conclusions : A brief overview of previous ICS-MCB applications demonstrates that the technique may provide an appreciable amount of unique data on chromosome abnormalities and organization in interphase nuclei. Fur­ thermore, the technique offers opportunities for evaluating these phenomena in the diseased human brain. Such opportunity seems to be critical for unraveling molecular and cellular mechanisms of neurodevelopmental and neurodegenerative disorders. Therefore, we conclude that ICS-MCB may represent an important part of molecular and cellular studies of neurodevelopmental and neurodegenerative disorders.

Introduction. Neurodevelopmental and neurodegenerative disorders have been sys tematically associated with genomic varia tions (i.e. chromosome abnormalities, copy number variations and single-gene mutations) [1][2][3][4]. Besides, genomic variations are com monly mosaic. Furthermore, somatic mosai cism is likely to be an important genetic mechanism for brain diseases. The most common types of somatic genomic variations are chromosomal mosaicism and instability [1,3,[5][6][7]. However, despite these observa tions, somatic chromosomal mosaicism is still under observed. This is more likely because of unacceptable neglect to techniques availa ble for studying intercellular genome variabil ity [1,7]. Fortunately, molecular cytogenetics does provide approaches towards studying genome variations at chromosomal level [8,9]. Probably, the most important molecu lar cytogenetic technique for studying chro mosomes in individual cells is interphase flu orescence in situ hybridization (FISH) [10]. The latter has been already shown to provide valuable data on chromosomal mosaicism and the contribution to brain pathology in neurodevelopmental and neurodegenerative disorders [7, 11, 12]. Currently, FISH still represents an important technology for studying chromoso mal imbalances and chromosome organization in interphase nuclei regardless of the introduc tion of post-genomic technologies (i.e. nextgeneration sequencing and microarray-based methods) [10, 13-15]. The present communica tion pays attention to a FISH-based technique for studying individual interphase chromo somes in their integrity in single cells -inter phase chromosome-specific multicolor band ing (ICS-MCB) -and to the applicability for studying neurodevelopmental and neurodegenerative disorders.

ICS-MCB applications.ICS-MCB
is a method combining interphase FISH and multi color chromosomal banding (a FISH-based approach toward banding several chromoso mal regions and subregions smaller than a chromosome arm through the use of microdis sected DNA probes). The application of ICS-MCB on human cellular nuclei provides the depiction of homologous interphase chromo somes in their integrity at molecular resolution (see Iourov et al. [16,17]). Actually, there is no true alternative to this technique for study ing human interphase chromosomes in their integrity in individual cells [7, 10, 18]. Previ ously, ICS-MCB has been applied to identify chromosomal abnormalities and instability in the diseased human brain. Furthermore, the technique might be used for determining nu clear chromosome organization in almost all human tissues.
Somatic chromosomal mosaicism and chromosome instability has been repeatedly associated with neurodevelopmental and neurodegenerative disorders [1,7,19,20]. More importantly, these types of genomic variability may be confined to the diseased brain. The phenomenon of brain-specific chromosomal mosaicism seems to play a significant role in the etiology of neurodevelopmental and neurodegenerative disorders [3,7,19,21]. For in stance, chromosomal instability, a process closely related to cancerization, has been un covered to mediate neurodegeneration using ICS-MCB. Interphase chromosome breaks (ICB) have been found to be the commonest type of chromosomal instability mediating cer ebellar neurodegeneration in ataxiatelangiectasia [22]. ICB are currently undetect able by any type of molecular (cytogenetic) techniques apart from ICS-MCB. Brain-specific aneuploidy and copy number variations have been shown to be implicated in molecular and cellular pathways neurodegeneration [3,19,23]. Aneuploidy of chromosomes 21 and X un covered by ICS-MCB has been found to be a common mechanism for Alzheimer's disease, one of the commonest neurodegenerative dis eases in elderly persons [24][25][26]. Currently, such types of genomic variability are suggested to be key elements of the Alzheimer's disease patho genetic cascade [27]. Age-specific chromoso mal mosaicism requires to be addressed by high-resolution single-cell molecular cytogenet ic techniques (i.e. ICS-MCB) [28,29]. Finally, chromosomal instability (chromothripsis) ap pears to mediate brain dysfunction in neurodevelopmental and neurodegenerative disorders [30]. In total, the phenomena identified using ICS-MCB have been recognized as genomic mechanisms of intercellular genetic variation in health and disease [31,32].
Alternatively, ICS-MCB may be applied for studying chromosome arrangement in inter phase nuclei [3,10,16,17,21]. It is to note that positioning of chromosomes in the nucleus and its impact on transcriptional genome activity and genome stability maintenance have not been evaluated in the majority of human tissues. The application of ICS-MCB would be certain ly valuable to fill this gap in our biomedical knowledge. It is highly likely that chromosome nuclear organization is specific for a variety of brain diseases including those leading to neurodevelopmental and neurodegenerative disor ders.
Taking into account previous experience, one may define a spectrum of targets for mo lecular (neuro) cytognetic studies of neurodevelopmental and neurodegenerative disorders using ICS-MCB. Figure schematically shows these ICS-MCB targets. The spectrum of ICS-MCB targets evi dences for high applicability of this molecular cytogenetic technique for studying brain dis eases. Recently, neurodevelopmental and neurodegenerative disorders have been shown to be mediated by a complex pattern of geneticenvironmental interactions. It is more probable that chromosomal abnormalities/instability (i.e. aneuploidy and ICB) are important elements of the pathogenetic cascade. In other words, envi ronmental effects interact with specific ge nomic susceptibility to the instability to cause aneuploidy and ICB [33]. Nuclear chromo some organization might be implicated in pathways to neurodevelopmental and neurodegenerative disorders in a similar way. There fore, further studies aimed at determination of molecular and cellular pathways to neurodevelopmental and neurodegenerative disorders would benefit from the application of ICS-MCB.
Conclusions. The evaluation of ICS-MCB applicability shows this technique to of fer a unique possibility to address chromoso mal instability and nuclear chromosome organ ization in human interphase nuclei. Since the overwhelming majority of human cells are likely to be in interphase, ICS-MCB represents an important tool for chromosomal and ge nomic research. In summary, complementary surveys of molecular and cellular (genetic and genomic) mechanisms of neurodevelopmental and neurodegenerative disorders are likely to require this interphase cytogenetic approach to chromosomal analysis.
No conflict o f interest was recorded with respect to this article.