This investigation was conducted to determine the relationship between
Y chromosome loss and increased micronucleus formation with age, We a
lso investigated the status of kinetochore proteins in the micronuclei
. Umbilical cord blood samples were obtained from 18 newborn males, an
d peripheral blood was obtained from 35 adult males ranging in age fro
m 22 to 79 years. Isolated lymphocytes from all 53 donors were culture
d and blocked with cytochalasin B. Two thousand binucleate cells per d
onor were scored using a modified micronucleus assay to determine the
kinetochore status of each micronucleus. This assay showed 23.8% of th
e micronuclei to be kinetochore-positive, while 76.2% of the micronucl
ei were kinetochore-negative. Cells were then hybridized with a 3.56-k
b biotinylated Y chromosome-specific probe. All micronucleate cells we
re relocated and their Y probe status was determined. A significant in
crease in Y-bearing micronuclei with age was observed. Metaphase cells
from the same samples were analyzed for the presence or absence of Y
chromosome. The relationship between Y chromosome-positive micronuclei
and Y chromosome-negative metaphase cells was highly significant, sug
gesting that Y chromosome-deficient metaphase cells result from cells
which had previously lost a Y chromosome due to micronucleation. The c
ause of micronucleus formation from a lagging Y chromosome appears pro
bably to be either a faulty or a diminished amount of kinetochore prot
ein.