Maternally and zygotically mutant arr2
embryos (coming from mothers whose whole germline constitutes from arr2
mutant cells only - created by the OvoD germline clone technique) show a segment polarity phenotype and no naked cuticle between denticle belts on the ventral epidermis (resulting in a lawn of denticles).
Embryos mutant for both maternal and zygotic arr2
show lawns of denticles uninterrupted by naked cuticle.
In clones mutant for arr2
, the peripheral ommatidia do not undergo programmed cell death and so fail to release their associated 2o
pigment cells to join the pigment rim. As a consequence, the pigment rim in arr2
clones is significantly reduced in relation to neighbouring wild-type tissue.
Somatic clones of arr2
homozygous cells in the wing pouch region of third instar wing discs are smaller on average than their wild-type twin spots (P=1.6x10-7
). Mutant wing pouch clones are associated with increased apoptosis marker expression. When these clones fall in the notum region of this disc there is no difference in mutant clone and twin spot size.
Homozygous clones are not recovered in the wing pouch when the clones are induced early, although small mutant clones are detected in the wing pouch and hinge cells.
Clones expressing arr2
that are induced at the anterior margin in the ventral part of the eye have extra ommatidia in the position normally occupied by the pigment rim. arr2
clones can violate the normal margin and grow out into the head region. Such ectopic eye tissue is heavily bristled. However, in clones that respect the normal eye boundary, the only observed phenotype is the presence of bristles adjacent to the head capsule.
Early induced clones do not survive well.
Clones in the wing cause notching with loss of margin bristles.
Homozygous clones in the eye produce two distinct effects that occur at roughly the same frequency. Firstly, homozygous clones induce ectopic differentiation of the retina ahead of the morphogenetic furrow. Secondly, clones that do not induce ectopic differentiation show clear repolarising effects in the equatorial/polar axis, inducing polarity reversals on their equatorial side. At the poles, the clones exert their maximal influence into surrounding wild-type tissue, inverting the polarity over many ommatidial rows. This effect diminishes progressively with the distance of the clone from the pole, disappearing at the equator. Within the clone, the chiralities of the ommatidia are not randomly arranged; in the equatorial region of the clone the ommatidia are inverted into the inappropriate form found in neighbouring wild-type tissue, but in the polar regions of the clone, the ommatidia are of the correct chiral form (the form found polar to the clone).