|
A summary drawing of the digestive system and the major routes of
membrane flow in P. multimicronucleatum. Membrane is collected
by the microtubular ribbons that extend from the cytopharynx. The
discoidal vesicles provide for new nascent DV membrane, acidosomes
bind to the surface of the nascent DV and small 100nm vesicles fuse
with the acidosomes. The nascent DV pinches from the cytopharynx by
endocytosis forming the phagosome (I) and then moves
posteriorly where the acidosomes fuse with the phagosome to form the
phagoacidosome (II) as the original phagosome membrane is
removed. This discoidal-derived membrane is recycled back to the
cytopharynx. The phagoacidosome becomes acid. Lysosomes then bind to
the phagoacidosome and later fuse to form the phagolysosome
(III). The fate of the acidosome membrane at this step is not
clear. Digestion occurs in the phagolysosome as lysosomes supply
hydrolases. When digestion is complete the hydrolases are retrieved in
tubules that round into secondary lysosomes. This retrieval results in
a hydrolase-free spent vacuole (IV). Presumably primary
lysosomes arising from the trans Golgi network and secondary lysosomes
will bind to new phagoacidosomes. Endocytosis, constitutive secretion
and regulated secretion in the form of trichocyst discharge as well as
trichocyst membrane retrieval enter and leave this trafficking process
at precise points. Figure published in Allen and Fok, Int. Rev. Cytol.
198:277-318, 2000, prepared by Dr. Tomomi Tani.
|
