Timing of genomic imprinting

[Jim Cummins]

Does anyone have any  information on when genomic imprinting is
completed in mammalian spermatogenesis?  There's a report of
fertilization by fusion of round spermatids with oocytes (mouse,
hamster) but so far no successful embryo development. 
This question is relevant to current techniques using micro-assisted
human fertilization by intracytoplasmic sperm injection (ICSI)  in
cases of severe male infertility.  There are already reports of
fertilization using very immature sperm from the rete testis.  Poor
chromatin condensation is significantly associated with male
infertility, and if imprinting is not completed until after the second
meiotic division this could lead to problems in embryo development.  
In addition, there are strong associations between epididymal blockage
( a common indication used for carrying out ICSI) and cystic fibrosis,
which is a bit worrying. 

Jim Cummins                   
School of Veterinary Studies
Murdoch University
Western Australia 6150  Tel +61-9-360 2668 Fax +61-9-310 4144
For every complex problem there's a simple solution.  And it's wrong!