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Fig. 1.12 Asl is essential for centriole duplication in vivo. Wild-type cells (control) contain both
a mother centriole (M) and its daughter centriole (D). Centrioles are labeled by Ana1-GFP
(green); PCM assembled around these centrioles are labeled for c-tubulin (red). In asl loss-of-
function mutant cells, the maternally contributed centrioles elongate but its duplication is
blocked. Modified from (Blachon et al.
2008
). (The fig is modified from Fig.
1.5
d in (Blachon
et al.
2008
)
because they cannot stand on their legs, walk, or fly [defects collectively referred
to as uncoordination (Kernan et al.
1994
)]. This uncoordination results from the
fact that flies with centrosomal defects have no mechanosensory cilia and cannot
sense the environment or their body parts.
The germline stem cells found in the testes originate from the first group of cells
that are generated early in embryonic development (pole cells) (Okada
1998
).
When germline stem cells divide to form a new stem cell and a spermatogonium,
the older centriole (the maternally contributed centriole) stays in the stem cells
while the newer centriole is inherited by the spermatogonium (Blachon et al.
2008
;
Yamashita et al.
2007
). A fly that is homozygous mutant for an essential centriole
component and cannot form new centrioles will have functional centrioles in the
germline stem cells that are made using maternal contribution, but will lack these
centrioles in the later progenitors.
Since germline stem cells in the developing Drosophila testes have two
maternally contributed centrioles, some of the first spermatogonium to form can
each inherit one maternally contributed centriole. These centrioles then duplicate
and elongate during spermatogenesis and end up in the first spermatids to form. By
that time maternal contribution of wild-type proteins becomes depleted. Following
maternally contributed centrioles of the spermatogonium and later in spermato-
genesis allows one to dissect the role of a particular protein under circumstances
where a centriole is present (Fig.
1.12
). Using this approach, it was found that
maternally contributed centrioles require Sas-4 to elongate but not Asl (Blachon
et al.
2009
; Blachon et al.
2008
). On the other hand, formation of the PCL can
form in Sas-4 mutants but not in Asl mutants (Blachon et al.
2009
) and Fig.
(
1.11
b).
