The distance from one nucleus to the next is variable in AGO2414 presyncytial and syncytial embryos compared to regular in wild-type,
with nuclei found clustered in some regions of the embryo while they
are absent in other regions. Many AGO2414 nuclei fail to migrate
to the surface, while others appear to reach the surface but then fall
back into the interior of the embryo, consequently the nuclear distribution
at the surface is quite irregular. In some regions there is a high
concentration of nuclei, often linked together in 'strings' of two,
three, or four incompletely separated nuclei, while in other regions
there are very few. There is also evidence that some nuclei may have
more than the normal complement of DNA while others may be missing
Defects in chromosomal migration are also evident prior to nuclear
migration in AGO2414 mutant embryos.
Consistent with the requirement for AGO2 in the proper execution
of the mitotic cycle, anomalous anaphase figures with incompletely
condensed and irregularly positioned chromosomes are observed in the
Nearly 10-15% of AGO2414 mutant embryos do not hatch.
A variety of anomalies are evident in AGO2414 embryos. In the early
cleavage stage embryo, nuclei can be fragmented and can appear to have
incompletely separated but still enter mitosis. In older embryos, asynchrony
is occasionally observed in incompletely separated nuclei.
During metaphase in AGO2414 embryos, nuclei appear to undergo a
normal mitosis in approximately half of the cases. In the other half,
defects such as 'orphan' centrosomes pairs are observed. While the
duplicated centrosomes occasionally remain in close proximity, most
appear to migrate to opposite poles. These 'orphan' centrosome pairs
are not associated with a mitotic spindle apparatus or with mitotic
chromosomes, nor does there appear to be any nearby interphase nucleus.
While other centrosome pairs appear to properly nucleate the mitotic
spindle apparatus, the spindles are abnormally short and do not extend
to the chromosomes or make connections with the centromeres. The chromosomes
often appear to be displaced from their normal position in the center
of the metaphase plate. In other cases there are DNA bridges that extend
between two adjacent mitotic figures. There are also 'mitotic spindle'
bridges that connect two different mitotic figures.
In half of AGO2414 embryos the cytoskeleton, normally a regular
lattice, is replaced by a broken network with irregularly shaped contractile
rings that vary in thickness from one part of the ring to the next.
Some of these scra-labelled rings appear to contain multiple nuclei,
while other rings have neither nuclei nor DNA.
The total number of pole cells is much reduced in AGO2414 embryos
(8, compared to 20 per embryo in wild-type). These pole cells are often
not positioned correctly at the very posterior or are separated from
each other by somatic cells. There is also a great deal of variability
in the number of pole cells in AGO2414 mutants compared to wild-type.
While some AGO2414 embryos have only two or three pole cells, there
are a few that have near wild-type numbers. This reduction in the number
of pole cells can be traced back to nuclear cycle 8-9 when migrating
nuclei first enter the posterior pole plasm. Several nuclear cycle
8-9 AGO2414 embryos have fewer pole buds than wild-type.