Abstract
Dynamins are universally conserved large guanosine triphosphatases,
which function as mechanoenzymes in
membrane scission. The primitive protozoan Giardia lamblia
has a single dynamin-related protein (GlDRP) with an
unusual domain structure. Giardia lacks a Golgi apparatus
but generates transient Golgi-like delay compartments
dubbed encystation-specific vesicles (ESVs), which serve
to accumulate and mature cyst wall proteins during differentiation
to infectious cyst forms. Here, we analyze the
function of GlDRP during growth and encystation and
demonstrate that it relocalizes from peripheral endosomal–
lysosomal compartments to nascent ESVs. We show
that GlDRP is necessary for secretion of the cyst wall
material and ESV homeostasis. Expression of a dominantnegative
GlDRP variant does not interfere with ESV formation
but blocks cyst formation completely prior to regulated
exocytosis. GlDRP colocalizes with clathrin at the cell
periphery and is necessary for endocytosis of surface proteins
to endosomal–lysosomal organelles in trophozoites.
Electron microscopy and live cell imaging reveal gross
morphological changes as well as functional impairment
of the endocytic system in cells expressing the dominantnegative
GlDRP. Thus, giardial DRP plays a key role in two
distinct trafficking pathways and in organelle homeostasis,
both essential functions for the proliferation of the parasite
in the gut and its transmission to a new host.
Gaechter, V