Excess crossovers impede faithful meiotic chromosome segregation in C. elegans
Fig 7
Oocytes can correct errors from excess COs in anaphase.
(A) Frequency of anaphase bridges in vector control (N = 52 at 15°C; N = 49 at 25°C) and lem-3(RNAi)-treated (N = 52 at 15°C; N = 37 at 25°C) meT7 anaphase I oocytes. Frequency of anaphase I bridges on meT7 increased following lem-3(RNAi) at 25°C (51.0%, 25/49 for control compared to 72.97%, 27/37 for lem-3(RNAi); P = 0.047, Fisher’s exact test, two-tailed). (B) Frequency of oocytes with DNA connecting the polar body and the MII spindle (“tethered polar body” category) or anueploidy in vector control (N = 48 at 15°C; N = 41 at 25°C) and lem-3(RNAi)-treated (N = 31 at 15°C; N = 28 at 25°C) metaphase II meT7 oocytes. Frequency of polar body extrusion delays or aneuploidy increased at 25°C (36.6%, 15/41 for control compared to 71.4%, 20/28 for lem-3(RNAi); P = 0.007, Fisher’s exact test, two-tailed). (C) Immunofluorescence of fixed anaphase II meT7 oocytes treated with lem-3(RNAi); shown are DNA (blue), microtubules (green), and SUMO (red). In 23/26 of lem-3(RNAi) oocytes in which the polar body tether (yellow arrow, bottom row) persisted into anaphase II, the tethered sister chromatid (meT7, magenta asterisk in bottom row) appeared to be segregating to the cell cortex (three examples shown, polar bodies denoted with white asterisks). Scale bars = 2.5μm. (D) Time-lapse montages of anaphase I and II in live lem-3 depleted wild type and meT7 oocytes expressing GFP::TBB-2 (microtubules) and mCherry::HIS-11 (histones). Yellow arrowheads indicate an anaphase I chromatin bridge. Blue arrowhead denotes a possible chromosome fragment after bridge breaking. White arrowheads point to a failure to segregate meT7 in Meiosis I and extrusion into the first polar body. Time zero is the time at which chromosome segregation appears to begin. Scale bars = 5μm. (E) Model for effects of supernumerary crossovers in C. elegans meiosis.