FISH and Chimps: Insights into Frequency and Distribution of Sperm Aneuploidy in Chimpanzees (Pan troglodytes)

Abstract

Numerical chromosomal aberrations in sperm are considered to be a major factor in infertility, early pregnancy loss and syndromes with developmental and cognitive disabilities in mammals, including primates. Despite numerous studies in human and farm animals, the incidence and importance of sperm aneuploidies in non-human primate remains mostly undetermined. Here we investigated the incidence and distribution of sperm aneuploidy in chimpanzees (Pan troglodytes), the species closest to human. We identify evolutionary conserved DNA sequences in human and chimpanzee and selected homologous sub-telomeric regions for all chromosomes to build custom probes and perform sperm-FISH analysis on more than 10,000 sperm nuclei per chromosome. Chimpanzee mean autosomal disomy rate was 0.057 ± 0.02%, gonosomes disomy rate was 0.198% and the total disomy rate was 1.497%. The proportion of X or Y gametes was respectively 49.94% and 50.06% for a ratio of 1.002 and diploidy rate was 0.053%. Our data provide for the first time an overview of aneuploidy in non-human primate sperm and shed new insights into the issues of aneuploidy origins and mechanisms.

Keywords: chromosome; cytogenetic; infertility; non-human primate; reproduction; spermatozoa.

Figure 1

(A) G-banding and (B) R-banding karyogram of Homo sapiens and Pan troglodytes. (C) Fluorescent karyogram with positions of all probes used for chromosome enumeration. For each pair, human chromosomes (HSA) are positioned on the left and chimpanzee chromosomes (PTR) on the right. Probes from the short arm of human chromosome 2 and chimpanzee chromosome 13 were labeled in Spectrum Green and the others in Spectrum Orange (the color combinations used for the analyses are listed in the Material and Methods section).

Figure 2

FISH analysis of chimpanzee spermatozoa with two (A–C) and three-color (D–H) in situ hybridization. Panels (A) to (C) are labeled with 1 Spectrum Green (SG)/19 Spectrum Orange (SO) probes with (A) displaying a normal nuclei, (B) a disomy of chromosome 19 and (C) a disomy of chromosome 1. Panels (D–H) are labeled with 21 Spectrum Aqua (SA)/X SG/Y SO probes with (E,F) displaying normal 21, X and 21, Y nuclei, and (D,G,H) displaying disomy of sex chromosomes. Scale = 10 µM.