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SUMMARY:Mixing mitosis and meiosis in Drosophila  - Dr Jean-René Huynh\, 
 Collège de France\, CIRB\, Paris  
DTSTART:20200305T130000Z
DTEND:20200305T140000Z
UID:TALK129520@talks.cam.ac.uk
CONTACT:Caroline Newnham
DESCRIPTION:At the beginning of meiosis\, chromosomes need to pair with th
 eir homologous partner and initiate recombination events that will ensure 
 exchange of genetic information and proper segregation during anaphase I. 
 Pairing events differ significantly between species. We and others recentl
 y uncovered in Drosophila that homologous chromosomes are not paired in pr
 imordial germ cells (PGCs)\, which are the first germ cells to be formed i
 n the embryo\; and that this absence of pairing is maintained for the auto
 somes until PGCs become germline stem cells (GSCs) in the adult. Surprisin
 gly\, of all cells in the adult fly\, the only cells with unpaired chromos
 omes are the ones bound for meiosis. We were surprised to find that pairin
 g takes place in premeiotic cells originating from GSCs and which undergo 
 four rounds of mitosis before entering meiosis. In Drosophila females\, we
  showed that homologous chromosomes start to pair when reaching the nuclea
 r envelope in the mitotic zone. Once at the membrane\, centromere movement
 s are highly dynamic and we demonstrated that these movements are caused b
 y rotations of the entire nucleus driven by microtubules and the SUN/KASH 
 (LINC) complex in females.\nMeiosis in Drosophila males is known to be ver
 y different from females: males do not form synaptonemal complexes\, males
  do not recombine and have no crossing-over\; yet\, males segregate their 
 chromosomes perfectly normally. We thus wanted to investigate how males ar
 e pairing their homologues. Our results show that the initial events are s
 trikingly similar to females: male GSCs have unpaired chromosomes and homo
 logues start to pair during the four mitotic divisions. Even more surprisi
 ngly\, we found that males do express SC proteins\, which only localize at
  centromeres and do not elongate along chromosome arms. However\, we found
  that chromosomes are much less dynamic than in females. I will present ou
 r latest results and model showing that males and females flies used simil
 ar molecular mechanisms but different kinetics to pair their homologous ch
 romosomes.\n
LOCATION:Biffen Lecture Theatre\, Department of Genetics\, Downing Site
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