Ultrastructure of the fragile X chromosome: new observations on the fragile site.
Using a nonair-drying modification of a method for longitudinal sectioning of metaphase spreads on glass slides [Wen et al., 1997], we have studied 14 preidentified X chromosomes (10 from fragile X specimens and 4 controls) with transmission electron microscopy (TEM). Four of 10 X chromosomes from fragile X specimens exhibited lighter chromatin density in the area of and distal to the fragile site, most pronounced under dark-field TEM. A clear line of separation at the fragile site locus was also observed by TEM in an X chromosome with no visible fragile site after Q-banding. We hypothesize that these areas of lighter density, including lines of separation, precede the appearance of the fragile site that is commonly observed using light microscopy.
Wen
G Y
GY
New York State Institute for Basic Research in Developmental Disabilities, Staten Island 10314, USA. gary@erols.com
Jenkins
E C
EC
Goldberg
E M
EM
Genovese
M
M
Brown
W T
WT
Wisniewski
H M
HM
D043283:Chromosome Fragile Sites; D002873:Chromosome Fragility / Q000235:genetics*; D005600:Fragile X Syndrome / Q000235:genetics*; D006801:Humans; D008854:Microscopy, Electron; D014960:X Chromosome / Q000648:ultrastructure*