Effects of sex chromosome aneuploidy on male sexual behavior

Abstract

Incidence of sex chromosome aneuploidy in men is as high as 1:500. The predominant conditions are an additional Y chromosome (47,XYY) or an additional X chromosome (47,XXY). Behavioral studies using animal models of these conditions are rare. To assess the role of sex chromosome aneuploidy on sexual behavior, we used mice with a spontaneous mutation on the Y chromosome in which the testis-determining gene Sry is deleted (referred to as Y(-)) and insertion of a Sry transgene on an autosome. Dams were aneuploid (XXY(-)) and the sires had an inserted Sry transgene (XYSry). Litters contained six male genotypes, XY, XYY(-), XXSry, XXY(-)Sry, XYSry and XYY(-)Sry. In order to eliminate possible differences in levels of testosterone, all of the subjects were castrated and received testosterone implants prior to tests for male sex behavior. Mice with an additional copy of the Y(-) chromosome (XYY(-)) had shorter latencies to intromit and achieve ejaculations than XY males. In a comparison of the four genotypes bearing the Sry transgene, males with two copies of the X chromosome (XXSry and XXY(-)Sry) had longer latencies to mount and thrust than males with only one copy of the X chromosome (XYSry and XYY(-)Sry) and decreased frequencies of mounts and intromissions as compared with XYSry males. The results implicate novel roles for sex chromosome genes in sexual behaviors.

Figure 1. Ejaculatory behavior of six male genotypes

(a) Percentage of males copulating to a criterion of behavioral ejaculation over all four behavioral tests. (b) Frequency of ejaculation over four behavioral tests. *Significantly lower than XYY⁻ (P < 0.05). n = numbers of subjects per group.

Figure 2. Latencies of male sexual behaviors of XY and XYY⁻ males

(a) Mean ± SEM of the average mount, thrust, intromission and ejaculation latencies over all four behavioral tests of all XY and XYY⁻ males. (b) Mean ± SEM of the average mount, thrust, intromission and ejaculation latencies over all four behavioral tests of XY and XYY⁻ males that copulated to a criterion of behavioral ejaculation. *Significantly longer than the XYY⁻ group (P < 0.05).

Figure 3. Latencies of male sexual behaviors of males with the Sry transgene

Mean ± SEM of the average (a) mount, (b) thrust (c) intromission and (d) ejaculation latencies over all four behavioral tests of all XYSry (n = 11), XYY⁻Sry (n = 13), XXSry (n = 13) and XXY⁻Sry (n = 7) males. Males with two X chromosomes had shorter mount, thrust and intromission latencies than males with one X chromosome. *P < 0.05.

Figure 4. Frequencies of male sexual behaviors of males with the Sry transgene

Mean ± SEM of the average number of (a) mounts, (b) thrusts, (c) intromissions and (d) ejaculations over four behavioral tests of XYSry (n = 10), XYY⁻Sry (n = 13), XXSry (n = 12) and XXY⁻Sry (n = 7) males. Males with two X chromosomes had decreased number of mounts, intromissions and ejaculations than males with one X chromosome. *P < 0.05.

Figure 5. Frequencies of male sexual behaviors of XY, XYSry, XYY⁻, XYY⁻Sry males

Mean ± SEM of the average number of (a) mounts, (b) thrusts, (c) intromissions and (d) ejaculations performed by the subset of males that ejaculated at least once. Here we compare four groups: XY (n = 4), XYSry (n = 7), XYY⁻ (n = 9) and XYY⁻Sry (n = 9). *Significantly fewer than XYSry. **Significantly fewer than XYY⁻ (P < 0.05).