Transition from a meiotic to a somatic-like DNA damage response during the pachytene stage in mouse meiosis
Fig 3
Types of chromosomal bridges found after irradiation.
SYCP3 protein in green. (A-I) Spread spermatocytes at pachytene, except (G), which is at zygotene. (A) Distal junction between two autosomes. (B) Distal junction between an autosome and a sex chromosome, in this case the X. (C-D) Interstitial junctions between autosomal bivalents. In (C) a bivalent with two bridges, each contacting a different bivalent, is shown. In the inset, a higher power view of one of the bridges is shown. The lateral element of the homologue involved in the bridge is split into two filaments. One filament remains associated with the homologous chromosome and the other is linked to the chromosome of the other bivalent. In (D) two bivalents are sharing a bridge. In this case, the bridge is a whole counterpart, which has invaded the other bivalent. A higher power view of the bridge is shown in the inset. (E) Interstitial junctions between an autosomal bivalent and the X chromosome (X). In (F) a bridge is formed between an autosomal bivalent and the Y chromosome (Y). (G) Chromosomal bridge within an autosomal bivalent. (H) Chromosomal bridge within the X chromosome (X). (I) Chromosomal bridge within the Y chromosome (Y). (J-L) Squashed spermatocytes. DNA was counterstained with DAPI and false colored in red. (J) Bridges are seen in 3-dimension conserved cells. During anaphase-I (K) and telophase-I (L), chromosomal fragments and connections (arrows) are observed. (M). Graph showing the frequency of cells showing at least one bridge at the different cell stages of prophase-I and at the different time points after irradiation. The number of cells with bridges increases with recovery time. Chromosomal connections are especially represented in early pachytene cells. n = total number of cells analyzed.