Transmission of a fully functional human neocentromere through three generations

An unusual Y chromosome with a primary constriction inside the long-arm het erochromatin was found in the amniocytes of a 38-year-old woman. The same Y chromosome was found in her husband and brother-in-law, thus proving that it was already present in the father. FISH with alphoid DNA showed hybridiz ation signals at the usual position of the Y centromere but not at the prim ary constriction. Centromere proteins (CENP)-A, CENP-C, and CENP-E could no t be detected at the site of the canonic centromere but were present at the new constriction, whereas CENP-B was not detected on this Y chromosome. Ex periments with 82 Y-specific loci distributed throughout the chromosome con firmed that no gross deletion or rearrangement had taken place, and that th e Y chromosome belonged to a haplogroup whose members have a mean alphoid a rray of 770 kb (range 430-1,600 kb), whereas that of this case was similar to 250 kb. Thus, this Y chromosome appeared to be deleted for part of the a lphoid DNA. It seems likely that this deletion was responsible for the sile ncing of the normal centromere and that the activation of the neocentromere prevented the loss of this chromosome. Alternatively, neocentromere activa tion could have occurred first and stimulated inactivation of the normal ce ntromere by partial deletion. Whatever the mechanism, the presence of this chromosome in three generations demonstrates that it functions sufficiently well in mitosis for male sex determination and fertility and that neocentr omeres can be transmitted normally at meiosis.