Infertility and aneuploidy in mice lacking a type IA DNA topoisomerase IIIβ

Abstract

We report that disruption of the mouse TOP3␤ gene encoding DNA topoisomerase III␤, one of the two mammalian type IA DNA topoisomerases, leads to a progressive reduction in fecundity. The litter size in crosses of top3␤ ؊/؊ mice decreases over time and through successive generations, and this decrease seems to reflect embryonic death rather than impaired fertilization. These observations are suggestive of a gradual accumulation of chromosomal defects in germ cells lacking DNA topoisomerase III␤, and this interpretation is supported by the observation of a high incidence of aneuploidy in the spermatocytes of infertile top3␤ ؊/؊ males. Cytogenetic examination of spermatocytes of wild-type mice also indicates that DNA topoisomerase III␤ becomes prominently associated with the asynaptic regions of the XY bivalents during pachytene, and that there is a time lag between the appearance of chromosome-bound DNA topoisomerase III␤ and Rad51, a protein known to be involved in an early step of homologous recombination. We interpret these findings, together with the known mechanistic characteristics of different subfamilies of DNA topoisomerases, in terms of a specific role of a type IA DNA topoisomerase in the resolution of meiotic double-Holliday junctions without crossing over. This interpretation is most likely applicable to mitotic cells as well and can explain the universal presence of at least one type IA DNA topoisomerase in all organisms.

Characterization ofSpo11-dependent and independent phospho-H2AX foci during meiotic prophase I in the male mouse

“…After several PBS washes, appropriate secondary antibodies were incubated for 1 hour at 37°C and slides were washed with PBS, and then mounted with Vectashield (Vector Laboratories). RAD51/DMC1 immunolabeling was performed as described in Kwan et al (Kwan et al, 2003). For in vivo experiment at least 30 cells were analyzed per animal.…”

Top3 Processes Recombination Intermediates and Modulates Checkpoint Activity after DNA Damage

“…Whereas lower eukaryotes generally contain only one type IA topoisomerase, human cells, like most vertebrates, possess at least two Top3 homologues, hTOPIII␣ and hTOPIII␤ (Hanai et al, 1996;Ng et al, 1999). In mice, mutation of TOP3␣ causes embryonic lethality (Li and Wang, 1998), whereas mutation of TOP3␤ causes a shortened life span (Kwan et al, 2003). Interestingly, in S. cerevisiae and S. pombe, deletion of SGS1 or rqh1 ϩ can largely suppress the phenotypes caused by deletion of TOP3 or top3 ϩ , respectively (Gangloff et al, 1994;Goodwin et al, 1999;Maftahi et al, 1999;Chakraverty et al, 2001).…”

A Journey in the World of DNA Rings and Beyond

“…The physiological importance of the mammalian DNA topoisomerases was further underscored by studies of the IIβ enzyme, again initiated by Wei, who found that, although embryos lacking this enzyme can develop to term, they die at birth (90). He observed that these newborns showed no sign of any muscular movements before they expired, which suggested to us that they probably suffered a muscular and/or neural defect.…”

“…I therefore contacted Steve Burden at New York University Medical School about a plausible collaboration, and our joint experiments soon established that the mutant mice indeed showed neuromuscular defects. Innervation of the diaphragm muscles by motor axons, for example, is defective, leading to a breathing impairment and death at birth (90).…”