Heated spermatozoa: effects on embryonic development and epigenetics.
BACKGROUND
Sperm chromatin is highly condensed and relatively resistant to chemical and physical treatments. The purpose of this study was to explore the highest temperature that sperm can tolerate and still produce live offspring.


METHODS
Mouse sperm were heated in a water bath at 50, 65, 80 or 95°C for 30 min before they were microinjected into mouse oocytes. Fertilization, embryo development and 1-cell embryo karyotypes were evaluated. Epigenetic reprogramming including DNA methylation and histone H3K4-trimethylation were evaluated by immunofluorescent staining.


RESULTS
The ability of mouse sperm to activate the egg after ICSI was heat sensitive; only 20% of eggs were activated by sperm that had been heated to 50°C and none was activated by sperm heated to 80°C. However, if eggs were activated artificially, mouse sperm subjected to 80°C for 30 min were able to produce live offspring, while 95°C treatment disabled sperm decondensation after ICSI. Once the heat-treated sperm nucleus had developed into a pronucleus, sperm chromatin was able to undergo normal active DNA demethylation and histone methylation. Aberrant chromosome rates increased from 16.3 to 100% when the temperature was raised from 50 to 95°C.


CONCLUSIONS
Heat treatment destroys integrity of sperm chromatin in a temperature-dependent manner. Eighty degree Celsius was the highest temperature that mouse sperm could withstand and still produce live offspring.
State Key Laboratory of Reproductive Biology,  Institute of Zoology, Chinese Academy of Sciences, Beijing,  China.
Shi-Bin
SB
Chao
Lei
L
Guo
Xiang-Hong
XH
Ou
Shi-Ming
SM
Luo
Zhen-Bo
ZB
Wang
Heide
H
Schatten
Guo-Lan
GL
Gao
Qing-Yuan
QY
Sun
D000818:Animals; D019175:DNA Methylation; D004624:Embryo Transfer; D047108:Embryonic Development; D044127:Epigenesis, Genetic; D005260:Female; D005306:Fertilization; D006361:Heating; D006657:Histones / Q000378:metabolism; D006358:Hot Temperature; D059785:Karyotype; D008297:Male; D008745:Methylation; D051379:Mice; D008810:Mice, Inbred C57BL; D008813:Mice, Inbred ICR; D011247:Pregnancy; D020554:Sperm Injections, Intracytoplasmic; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000502:physiology*
D006657:Histones