Calcium- and polyphosphate-containing acidocalcisomes in chicken egg yolk

Area of Science:

• Biochemistry
• Cell Biology
• Developmental Biology

Background:

• Inorganic polyphosphate (Poly P) is a polymer of phosphate residues with diverse functions.
• While Poly P is known in simpler organisms, its presence in complex eukaryotes is less understood.
• Poly P often accumulates with calcium in acidic vesicles called acidocalcisomes.

Purpose of the Study:

• To investigate the presence and localization of Poly P in chicken egg yolks.
• To characterize the organelle containing Poly P in yolk.

Main Methods:

• DAPI staining to visualize Poly P.
• X-ray microanalysis and elemental mapping for elemental composition.
• Acridine Orange staining and agarose gel electrophoresis for Poly P detection.

Main Results:

• A significant amount of phosphorus in chicken egg yolk is Poly P.
• Poly P is localized in electron-dense vesicles within larger vacuoles in the yolk.
• These vesicles contain various elements (Ca, K, Na, Mg, P, Cl, Fe, Zn) and stain with Acridine Orange.
• 16% of the total phosphate in yolk organelles is Poly P.
• Poly P content remained stable during early embryogenesis, but chain length decreased.

Conclusions:

• A novel organelle, resembling acidocalcisomes within larger vacuoles, was identified in chicken egg yolk.
• The elemental composition of these organelles mirrors the yolk's overall elemental composition.
• These findings suggest these organelles are crucial storage compartments within the egg.