Fluorescence in situ hybridization-based approaches for detection of 12p overrepresentation, in particular i(12p), in cell lines of human testicular germ cell tumors of adults.

Overrepresentation of the short arm of chromosome 12 is frequently detected in human testicular germ cell tumors of adolescents and adults (TGCT). This overrepresentation mostly results from the formation of an isochromosome: i(12p). Whether the overrepresentation consistently involves the complete 12p arm including the centromere is still unclear. We studied five TGCT-derived cell lines (NT2, 2102Ep, H12.1, NCCIT, and S2), combining conventional chromosome banding, fluorescence in situ hybridization (FISH), and comparative genomic hybridization (CGH) to investigate the suitability of each of these techniques to detect aberrations involving chromosome 12. Karyotyping showed one or more i(12p)s in NT2, 2102Ep, H12.1, and S2. However, FISH with a centromere-specific probe (p alpha 12H8), a 12p "paint" and a 12p11.2--p12.1 region-specific probe yeast artificial chromosome (YAC)#5 and CGH could not confirm the presence of an i(12p) in S2. Additional randomly distributed 12p sequences were detected by FISH in H12.1, NCCIT, and S2. In most of these cases, (a part of) the centromere was included. All overrepresented 12p regions, except for those in S2, showed hybridization with YAC#5. CGH showed increased copy numbers of the complete 12p arm in the cell lines with one or more i(12p)s but no overrepresentation was noted in the cell lines without i(12p). In metaphase spreads, the centromeric block of the i(12p)s differed in size as compared with those of normal chromosomes 12. This was rarely noted in interphase nuclei. A decrease in size of the centromeric block in 2102Ep and H12.1 caused a weak FISH signal, which was difficult to detect, especially in interphase nuclei. The ratio between p alpha 12H8- and YAC#5-derived signals reflected the presence or absence of one or more i(12p)s. Our results indicate that double FISH with a centromere- and a 12p-specific probe can be used to detect 12p overrepresentation [including i(12p)] in TGCT both in metaphase spreads and interphase nuclei. CGH confirmed the relative overrepresentation of 12p sequences as detected by FISH and showed that in these cell lines the complete 12p was involved.

Comparative genomic hybridization of germ cell tumors of the adult testis: confirmation of karyotypic findings and identification of a 12p-amplicon.

Comparative genomic hybridization (CGH) was carried out on 15 primary testicular germ cell tumors (TGCT) of adolescents and adults and two metastatic residual tumors after chemotherapeutic treatment. The results were compared with karyotypic data obtained form the same tumor specimens after direct harvesting of metaphases or short-term in vitro culture. Both techniques revealed that the most consistent abnormality in primary TGCT is gain of 12p-sequences. Although in most cases over-representation of the complete short arm was observed, CGH revealed a specific amplification of 12p11.1-p12.1 region in two independent primary tumors. In addition, loss of (parts of) chromosome 13 (always involving q31-qter), and gain of (parts of) chromosome 7 (mostly involving q11), (parts of) chromosome 8, and the X chromosome were detected in more than 25% of the tumors by this latter technique. Loss of 6q15-q21 in both residual tumors analyzed may suggest a role for this anomaly in acquired resistance to chemotherapeutic treatment. Overall, the CGH analyses confirmed gains and losses of certain chromosomal regions in TGCT as observed by karyotyping, and thus support their role in the development of these neoplasms. The amplification of a restricted region of 12p in primary TGCT confirms and extends our previous observations and, as such, represents an important step forward in the identification of gene(s) on 12p relevant for the pathogenesis of these tumors.