Dt. Schneider et al., Multipoint imprinting analysis indicates a common precursor cell for gonadal and nongonadal pediatric germ cell tumors, CANCER RES, 61(19), 2001, pp. 7268-7276
Pediatric germ cell tumors (GCTs) commonly arise at extragonadal sites. It
has been proposed that nongonadal GCTs arise from ectopic primordial germ c
ells that have aberrantly migrated during embryogenesis. During a time betw
een their migration and development to mature gametes, primordial germ cell
s are characterized by their lack of imprinting. which can be assessed by t
he evaluation of allelic gene expression and DNA methylation in differentia
lly methylated control regions. To elucidate the cellular origin of nongona
dal GCTs, we evaluated the imprinting status of 21 gonadal and 21 nongonada
l pediatric GCTs. Allele-specific H19 and IGF-2 expression was assessed wit
h reverse transcription-PCR followed by digestion at polymorphic restrictio
n sites. DNA methylation was evaluated after bisulfite modification, PCR am
plification, and restriction digestion at a consistently methylated CpG din
ucleotide within the 5' flanking region of the SNRPN gene. These results we
re compared with genetic gains and losses determined by comparative genomic
hybridization. Seven of 15 informative tumors showed biallelic H19 express
ion, and 8 of 17 informative tumors showed biallelic IGF-2 expression. The
frequency of biallelic gene expression was comparable in gonadal and non-go
nadal GCTs. Sixteen of 19 gonadal GCTs and 17 of 21 nongonadal GCTs showed
absence of methylation of SNRPN consistent with loss of imprinting. One tes
ticular GCT and three nongonadal GCTs showed a somatic methylation pattern.
Two ovarian teratomas and one mediastinal teratoma showed only methylated
SNRPN, consistent with entry into meiosis. Twenty-one of 22 non-GCT control
samples showed a somatic methylation pattern. Gonadal and nongonadal germ
cell tumors are derived from primordial germ cells that have consistently l
ost the imprinting of SNRPN and partly lost imprinting of H19 and IGF-2. Be
cause the imprinting pattern of the latter genes differs from that found in
testicular GCTs of adult patients, our data suggest that pediatric GCTs ar
ise from a different stage of germ cell development.