Chromosome painting analysis of early oogenesis in human trisomy 18

Abstract

We have used chromosome 18-specific painting probes to analyze early stages of oogenesis in two human trisomy 18 fetuses. At leptotene, a diffuse, nonlinear chromosomal fluorescence was detected as one (27%), two (42%), or three (31 %) signals in 534 cells. The variation in size of these signals implies the possibility of associations between homologs prior to zygotene. At pachytene, about 75 % (339/453) of the cells had a trivalent configuration, and almost half of these cells exhibited almost complete triple synapses. Approximately 24% of the pachytene cells demonstrated a bivalent:univalent configuration, and 1 % exhibited complete asynapsis. Our data imply that triple synapses may be a regular feature of meiosis involving multivalents.

Pairing and synapsis in oocytes from female fetuses with euploid and aneuploid chromosome complements

“…In summary, we conclude that the present study agrees with previous studies performed in euploid oocytes in which a high pairing process efficiency was described (Cheng & Gartler 1994, Cheng et al 1995, Roig et al 2005a. Our study presents the first analysis of the pairing process for chromosome 13 in oocytes from fetuses with trisomy 13.…”

“…As has been reported in earlier studies (Cheng et al 1995, 1998, Roig et al 2005a, 2005b for chromosomes 13, 18, and 21, we have observed that pairing of the 21 and X homologues starts during the late leptotene stage. Since the first piece of evidence of telomeric clustering has been detected during the leptotene/zygotene transition in human oocytes (Roig et al 2004(Roig et al , 2005b, as was already proposed in humans (Bojko 1983) and demonstrated in other species (Scherthan 2003), these results seem to support the hypothesis that bouquet topology promotes homologue encounter and facilitates the synaptic process during meiotic prophase.…”

“…The results presented in Table 2 show that chromosome pairing, as defined by the presence of a single WCP signal in the oocyte, in human euploid oocytes starts at the leptotene stage for both homologue pairs, as described previously for chromosomes 13, 18, and 21 (Cheng et al 1995, 1998, Roig et al 2005a, 2005b. Although the pairing process of chromosome 21 progresses faster than that of the X chromosome, it shows a higher error rate (0.3% of the oocytes presented two separate chromosome 21s at the pachytene stage), whereas this was not observed for the X chromosome in any oocyte (Fisher F-test, PZ0.507), these differences between two chromosomes being not statistically significant.…”

“…Nevertheless, some papers have studied human oocyte I using classical approaches mainly focusing on the establishment of the time frame in which meiotic prophase takes place in the human female, but also analyzing how homologues synapse (Ohno et al 1962, Baker 1963, Blandau 1969, Kurilo 1981, Bojko 1983, Speed 1985, Garcia et al 1987, 1989. Fluorescence in situ hybridization (FISH) has enabled the analysis of particular homologue pairing processes of euploid and aneuploid oocytes using whole chromosome probes (WCP) alone or combined with locus identification probes (Cheng & Gartler 1994, Cheng et al 1995, 1998, Cheng & NaluaiCecchini 2004, Roig et al 2005a or particular sets of probes to study oocytes with rearranged genomes (Cheng et al 1999, Cheng & Naluai-Cecchini 2004. More recently, studies have used immunofluorescence (IF) to primarily analyze meiotic recombination (Barlow & Hultén 1997, Hartshorne et al 1999, Roig et al 2004, 2005b, Lenzi et al 2005.…”

Chromosome 18 pairing behavior in human trisomic oocytes. Presence of an extra chromosome extends bouquet stage

“…The meiotic division is blocked until the female enters puberty. Despite the difficulties associated with the study of human female meiotic prophase, some aneuploid ovaries have been studied using classical staining techniques (Luciani et al 1976, Wallace & Hulten 1983, Speed 1984, fluorescent in situ hybridization (FISH) (Cheng et al 1995(Cheng et al , 1998 or immunofluorescent (IF) (Barlow et al 2002) techniques.…”