Calcium- and polyphosphate-containing acidocalcisomes in chicken egg yolk.
BACKGROUND
Poly P (inorganic polyphosphate) is a polymer formed by P(i) residues linked by high-energy phosphoanhydride bonds. The presence of poly P in bacteria, fungi, algae and protists has been widely recognized, but the distribution of poly P in more complex eukaryotes has been poorly studied. Poly P accumulates, together with calcium, in acidic vesicles or acidocalcisomes in a number of organisms and possesses a diverse array of functions, including roles in stress response, blood clotting, inflammation, calcification, cell proliferation and apoptosis.


RESULTS
We report here that a considerable amount of phosphorus in the yolk of chicken eggs is in the form of poly P. DAPI (4',6-diamidino-2-phenylindole) staining showed that poly P is localized mainly in electron-dense vesicles located inside larger vacuoles (compound organelles) that are randomly distributed in the yolk. These internal vesicles were shown to contain calcium, potassium, sodium, magnesium, phosphorus, chlorine, iron and zinc, as detected by X-ray microanalysis and elemental mapping. These vesicles stain with the acidophilic dye Acridine Orange. The presence of poly P in organellar fractions of the egg yolk was evident in agarose gels stained with Toluidine Blue and DAPI. Of the total phosphate (Pi) of yolk organelles, 16% is present in the form of poly P. Total poly P content was not altered during the first 4 days of embryogenesis, but poly P chain length decreased after 1 day of development.


CONCLUSIONS
The results of the present study identify a novel organelle in chicken egg yolk comprising acidic vesicles with a morphology, physiology and composition similar to those of acidocalcisomes, within larger acidic vacuoles. The elemental composition of these acidocalcisomes is proportionally similar to the elemental composition of the yolk, suggesting that most of these elements are located in these organelles, which might be an important storage compartment in eggs.
Ramos
Isabela B
IB
Department of Cellular Biology and Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602, USA.
Miranda
Kildare
K
Ulrich
Paul
P
Ingram
Peter
P
LeFurgey
Ann
A
Machado
Ednildo A
EA
de Souza
Wanderley
W
Docampo
Roberto
R
D000143:Acids; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D002645:Chickens / Q000378:metabolism*; D022162:Cytoplasmic Vesicles / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004530:Egg Yolk / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D004577:Electron Probe Microanalysis; D047108:Embryonic Development / Q000187:drug effects; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D018942:Macrolides / Q000494:pharmacology; D011122:Polyphosphates / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism
D000143:Acids; D018942:Macrolides; D011122:Polyphosphates; C057620:bafilomycin A; D025262:Vacuolar Proton-Translocating ATPases; D002118:Calcium