Sperm nucleosomes disassembly is a requirement for histones proteolysis during male pronucleus formation.
We had previously reported that a cysteine-protease catalyzes the sperm histones (SpH) degradation associated to male chromatin remodeling in sea urchins. We found that this protease selectively degraded the SpH leaving maternal cleavage stage (CS) histone variants unaffected, therefore we named it SpH-protease. It is yet unknown if the SpH-protease catalyzes the SpH degradation while these histones are organized as nucleosomes or if alternatively these histones should be released from DNA before their proteolysis. To investigate this issue we had performed an in vitro assay in which polynucleosomes were exposed to the active purified protease. As shown in this report, we found that sperm histones organized as nucleosomes remains unaffected after their incubation with the protease. In contrast the SpH unbound and free from DNA were readily degraded. Interestingly, we also found that free DNA inhibits SpH proteolysis in a dose-dependent manner, further strengthening the requirement of SpH release from DNA before in order to be degraded by the SpH-protease. In this context, we have also investigated the presence of a sperm-nucleosome disassembly activity (SNDA) after fertilization. We found a SNDA associated to the nuclear extracts from zygotes that were harvested during the time of male chromatin remodeling. This SNDA was undetectable in the nuclear extracts from unfertilized eggs and in zygotes harvested after the fusion of both pronuclei. We postulate that this SNDA is responsible for the SpH release from DNA which is required for their degradation by the cysteine-protease associated to male chromatin remodeling after fertilization.
Iribarren
Claudio
C
Department of Biochemistry and Molecular Biology, Universidad de Concepción, Casilla 160-C, Concepción, Chile.
Morin
Violeta
V
Puchi
Marcia
M
Imschenetzky
María
M
D000818:Animals; D042002:Chromatin Assembly and Disassembly / Q000187:drug effects / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000494:pharmacology / Q000502:physiology; D005260:Female; D005306:Fertilization; D006657:Histones / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008540:Meiosis / Q000502:physiology; D009707:Nucleosomes / Q000737:chemistry / Q000187:drug effects / Q000648:ultrastructure*; D012617:Sea Urchins; D013094:Spermatozoa / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D015053:Zygote / Q000737:chemistry / Q000648:ultrastructure
D006657:Histones; D009707:Nucleosomes; D003546:Cysteine Endopeptidases