Yolk platelets in artemia
embryos: are they really storage sites of immature mitochondria?
A.H. Warner, P.P.Y. Chu, M.F. Shaw, G. Criel-2002
Comparative Biochemistry and Physiology B:
Biochemistry and Molecular Biology, 132(2): 491-503 (from Current Contents)
Abstract :
We have used semi-quantitative polymerase chain
reaction (PCR) technology to determine the mitochondrial DNA (mtDNA) content
of yolk platelets isolated from embryos of the brine shrimp, Artemia
franciscana, and ultrastructual analysis of yolk platelet formation to
determine whether these organelles contain mitochondria as reported
previously. Using six different isolation and purification protocols, we
found one yolk platelet preparation to be devoid of mtDNA, while four yolk
platelet preparations contained mtDNA ranging from 16.4 to 85 pg/10(6) yolk
platelets. One preparation contained 600 pg mtDNA per 10(6) yolk platelets.
Based on our PCR analyses, the mtDNA component of Artemia yolk platelets
represented 0.16-4.5% of the total DNA isolated from the platelets. We
calculated that Artemia yolk platelets contain, on average, approximately
1.78 molecules of mtDNA/platelet. Direct analysis of mtDNA in 'free'
mitochondria isolated from yolk platelet-free preparations of Artemia
embryos and newly hatched larvae yielded 0.76-0.80 ng/animal. Based on these
values, the mtDNA content of yolk platelets was approximately 0.2% of total
mtDNA in Artemia embryos. Microscopic analysis of yolk platelet
formati6nAuring oogenesis in Artemia failed to show the inclusion of
mitochondria during the assemblage of yolk platelets. The
'mitochondria-like' structures that appear in yolk platelets during their
utilization lack the well defined inner and outer membranes characteristic
of mitochondria making it unlikely that the yolk platelet inclusions are
mitochondria. Our results from PCR technology and ultrastructure analysis
demonstrate that mtDNA in yolk platelets of Artemia franciscana embryos is a
minor component of the total mtDNA in the embryo, and they fail to support
the notion that yolk platelets in Artemia are a major source of immature
mitochondria for development.
(Univ Windsor, Dept Biol Sci, Windsor, ON N9B 3P4,
Canada, e-mail: warner1@uwindsor.ca)