title: Thoughts about SLC16A2, TSIX and XIST gene like sites in the human genome and a potential role in cellular chromosome counting.
abstract: BACKGROUND
  Chromosome counting is a process in which cells determine somehow their intrinsic chromosome number(s). The best-studied cellular mechanism that involves chromosome counting is 'chromosome-kissing' and X-chromosome inactivation (XCI) mechanism. It is necessary for the well-known dosage compensation between the genders in mammals to balance the number of active X-chromosomes (Xa) with regard to diploid set of autosomes. At the onset of XCI, two X-chromosomes are coming in close proximity and pair physically by a specific segment denominated X-pairing region (Xpr) that involves the SLC16A2 gene.
  
  
  RESULTS
  An Ensembl BLAST search for human and mouse SLC16A2/Slc16a2 homologues revealed, that highly similar sequences can be found at almost each chromosome in the corresponding genomes. Additionally, a BLAST search for SLC16A2/TSIX/XIST (genes responsible for XCI) reveled that "SLC16A2/TSIX/XIST like sequences" cover equally all chromosomes, too. With respect to this we provide following hypotheses.
  
  
  OBJECTIVE
  If a single genomic region containing the SLC16A2 gene on X-chromosome is responsible for maintaining "balanced" active copy numbers, it is possible that similar sequences or gene/s have the same function on other chromosomes (autosomes). SLC16A2 like sequences on autosomes could encompass evolutionary older, but functionally active key regions for chromosome counting in early embryogenesis. Also SLC16A2 like sequence on autosomes could be involved in inappropriate chromosomes pairing and, thereby be involved in aneuploidy formation during embryogenesis and cancer development. Also, "SLC16A2/TSIX/XIST gene like sequence combinations" covering the whole genome, could be important for the determination of X:autosome ratio in cells and chromosome counting.
  
  
  CONCLUSIONS
  SLC16A2 and/or SLC16A2/TSIX/XIST like sequence dispersed across autosomes and X-chromosome(s) could serve as bases for a counting mechanism to determine X:autosome ratio and could potentially be a mechanism by which a cell also counts its autosomes. It could also be that such specific genomic regions have the same function for each specific autosome. As errors during the obviously existing process of chromosome counting are one if not the major origin of germline/somatic aneuploidy the here presented hypotheses should further elaborated and experimentally tested.
authors: Croatian Institute for Brain Research, School of Medicine University of Zagreb, Salata 12, 10000 Zagreb, Croatia.
authors: Martina
authors: M
authors: Rinčić
authors: Mental Health Research Center, Moscow, 117152 Russia ; Ministry of Health of Russian Federation, Separated Structural Unit "Clinical Research Institute of Pediatrics" at Pirogov Russian National Research Medical University, Moscow, 125412 Russia ; Moscow State University of Psychology and Education, Moscow, 127051 Russia.
authors: Ivan Y
authors: IY
authors: Iourov
authors: Institute of Human Genetics, Jena University Hospital, Friedrich Schiller University, Kollegiengasse 10, D-07743 Jena, Germany.
authors: Thomas
authors: T
authors: Liehr
keywords: Chromosome counting; Chromosome kissing; Chromosome territories; SLC16A2; Sequence similarity; TSIX; X-chromosome inactivation; XIST