X-AUTOSOME AND X-Y TRANSLOCATIONS IN FEMALE CARRIERS: X-CHROMOSOME INACTIVATION EASILY DETECTABLE BY 5-ethynyl-2-deoxyuridine (EdU)
Donat M1, Louis a2, Kreskowski K1, Ziegler M1, Weise a1, schreyer I1,3, Liehr t1,*
*Corresponding Author: Dr. thomas Liehr, Universtätsklinikum Jena, Institut für Humangenetik, am Klinikum 1, D-07747 Jena, Germany. tel: +49-3641-939-68-50. Fax. +49-3641-939-68-52. e-mail: thomas.Liehr@ med.uni-jena.de
page: 87

INTRODUCTION

the X-chromosome inactivation process (XCI) in mammalian female cells has been known for decades [1]. the goal of XCI is to balance the number of active Xchromosomes (Xa) with respect to a diploid set of autosomes. as we recently summarized: “Dosage compensation between genders in mammals is achieved by keeping only one Xa per diploid set of autosomes. therefore, the majority of genes on one of the two X-chromosomes in female mammals is silenced and denoted as inactive Xchromosome (Xi) or Barr body” [2]. Interestingly, the molecular mechanism of XCI is not yet understood in detail, and especially, the choice of which of the present X-chromosomes have to be inactivated, remains overall enigmatic [2]. However, the X inactivation center as initial starting point of XCI has been identified, and the whole process was broken down to four stages including initiation, speeding, maintenance and reactivation [3]. In a normal female, the inactivation of one of the two Xchromosomes per cell is random; i.e., in ~50.0% of the cells the paternal and in the other ~50.0% of the cells the maternal X-chromosome is active. In the case of balanced X-Y- or X-autsome-translocations, the X-inactivation becomes skewed. this can be due to the fact that only those cells are viable in which the whole autosomal content involved in the translocation remains active [4]. Identification of derivatives of X-chromosomes in females raises the question about the pattern of XCI. previously, bromodeoxyuridine (5-bromo-2’-deoxyuridine; BUdr) was used to discriminate Xi from Xa in metaphase chromosomes [5]. However, recently a more reliable protocol was established based on 5-ethynyl-2’-deoxyuridine (edU) [6]. the edU is a labeled nucleoside analog of thymidine and it is incorporated during DNa synthesis of the cultivated blood cells. It is a marker that can highlight late replication regions and at the same time Xi. Here we report two female cases of X-autosome translocation (mother and daughter) and one female with an X-Y translocation leading to skewed X-inactivation. Molecular cytogenetics characterized the underlying chromosomal aberrations, and edU-method according to sisdelli et al. [6], could clearly identify the different patterns of X-inactivation.



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