Occurrence of pre-MBT synthesis of caspase-8 mRNA and activation of caspase-8 prior to execution of SAMDC (S-adenosylmethionine decarboxylase)-induced, but not p53-induced, apoptosis in Xenopus late blastulae.
Overexpression of S-adenosylmethionine decarboxylase (SAMDC) in Xenopus fertilized eggs activates caspase-9 and executes maternal program of apoptosis shortly after midblastula transition (MBT). We find that overexpression of caspase-8 and p53, like that of SAMDC, induces apoptosis in Xenopus late blastulae. The apoptosis induced by p53 was abolished by injection of mRNA for xdm-2, a negative regulator of p53, and by injection of a peptide inhibitor or a dominant-negative type mutant of caspase-9, but not caspase-8. The apoptosis induced by SAMDC was not abolished by injection of xdm-2 mRNA, but was abolished by injection of a peptide inhibitor or a dominant-negative type mutant mRNA of both caspase-9 and caspase-8. Unlike caspase-9 mRNA, caspase-8 mRNA did not occur as a maternal mRNA rather induced to be expressed during cleavage stage (pre-MBT stage) by overexpression of SAMDC but not p53. Furthermore, while activities to process procaspase-8 and procaspase-9 appeared in SAMDC-overexpressed apoptotic embryos, the activity to process procaspase-8 did not appear in p53-overexpressed apoptotic embryos. We conclude there are at least two pathways in the execution of the maternal program of apoptosis in Xenopus embryos; one being through do novo expression of caspase-8 gene during cleavage stage, and the other without involvement of caspase-8.
Shiokawa
Koichiro
K
Laboratory of Molecular Embryology, Department of Biological Science, Graduate School of Sciences, The University of Tokyo, 7-3 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. shiokawa@nasu.bio.teikyo-u.ac.jp
Takayama
Eiji
E
Higo
Takayasu
T
Kuroyanagi
Shinsaku
S
Kaito
Chikara
C
Hara
Hiroshi
H
Kajitani
Masayuki
M
Sekimizu
Kazuhisa
K
Tadakuma
Takushi
T
Miura
Kin-Ichiro
K
Igarashi
Kazuei
K
Yaoita
Yoshio
Y
D012437:Adenosylmethionine Decarboxylase / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D036703:Blastula / Q000166:cytology / Q000378:metabolism*; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D004789:Enzyme Activation; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000033:anatomy & histology / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*
D010940:Plant Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D016159:Tumor Suppressor Protein p53; D053181:Caspase 8; D020169:Caspases; D012437:Adenosylmethionine Decarboxylase; C078570:SAMDC protein, Solanum tuberosum