Biology Reference
In-Depth Information
In some mutants of centrosomal proteins, such as bld10, sterility is caused by an
abnormal sperm flagellum (Mottier-Pavie and Megraw,
2009
). In other mutants,
such as cnn, sterility is a result of meiosis defects followed by abnormal differ-
entiation of the motile sperm (Li et al.
1998
). However, in the most severe cen-
trosomal mutants (for example, asl, sas-4, sas-6, plk4, ana1) sterility is caused by a
combination of all of these mechanisms; the flies are uncoordinated, fail in mei-
osis, and do not form flagella (Basto et al.
2006
; Bettencourt-Dias et al.
2005
;
Blachon et al.
2009
; Blachon et al.
2008
; Martinez-Campos et al.
2004
; Rodrigues-
Martins et al.
2007a
). While, defects in sperm motility, meiosis, or proprioception
are not restricted to centrosomal mutations, the combination of these three phe-
notypes is a very strong indication of a mutation in a centrosomal protein (see
below).
1.6.5 Mechanosensory Mutants
Several centrosome and basal body-specific proteins were identified by a screen
for mechanosensory mutants. This screen led to the identification of the basal body
protein unc (Baker et al.
2004
), the mecB allele of ana1 (Blachon et al.
2009
), and
the mecD allele of asl (Blachon et al.
2008
).
A screen for mechanosensory mutants looks for adult lethal mutations that have
no or an abnormal mechanoreceptor current. Since the mechanosensory apparatus
is located in cilia, loss of the centrosome results in a loss of the mechanoreceptor
current. Therefore, as in mutants of genes involved in various aspects of mecha-
notransduction (Chung et al.
2001
; Walker et al.
2000
), centriolar mutants are
adult lethal and have no mechanoreceptor current (Fig.
1.8
).
1.6.6 PCL Mutants
The PCL is a centriolar structure resembling an early intermediate in centriole
biogenesis in its composition and in the genetic pathway that underlies its for-
mation (Blachon et al.
2009
). Since the PCL is similar to an early centriolar
intermediate, it was postulated that it should be possible to identify mutants of
genes required in early centriole formation by screening for mutants that do not
form a normal PCL.
Use of this approach led to the discovery of a mutant in the Drosophila ortholog
of Poc1. Since it is thought that the PCL is related to male fertility, male sterile
mutants were screened for PCL defects. PCL presence was scored using a cent-
riolar protein that labels the PCL strongly (Ana1). Poc1 is a conserved centrosomal
protein found in protists and mammals and its localization suggests that it plays a
role in early centriole formation (Blachon et al.
2009
; Keller et al.
2009
; Keller
et al.
2005
; Pearson et al.
2009
).
