mutant embryos display defects in the actin dynamics in the amnioserosa cells compared to controls.
In embryos from females heterozygous for shgg317
, an average of 3.7 PGCs are left outside the midgut with 64% of embryos exhibiting a phenotype.
homozygous embryos gonad compaction is sometimes initiated, but often does not proceed to completion. The three clusters of somatic gonadal precursors (SGPs) from parasegments (PS) 10-12 are able to associate correctly with one another, and with germ cells, to form a cohesive group. However, these cells often remain loosely associated and spread over more than one parasegment, rather than compacting tightly in PS10. In the most severe cases, compaction from PS10-12 to PS10 appears completely blocked. In weaker examples, compaction is initiated but not completed, resulting in partially compacted and misshapen gonads. During ensheathment of germ cells by gonadal mesoderm in these embryos the gonadal mesoderm cells fail to make cellular extensions between and around the germ cells. Phenotypes are stronger in these embryos than in shg2
homozygotes. This is true, both for the compaction phenotype (22% severe, 41% weak, n=49 in shgg317
homozygotes; 3% severe, 50% weak, n=36 in shg2
homozygotes) and the ensheathment phenotype, but the severity of these two phenotypes do not correlate with each other. In male shgg317
homozygous embryos male specific gonadal precursors often fail to join the posterior of the male gonad (42% male embryos n=49). Offspring from heterozygous shgg317
/+ females are viable, but the embryos have a significant germ cell migration defect. Offspring from the reciprocal cross using shgg317
/+ males show no germ cell migration defect.
Class IV allele: mutants lack all head and ventral cuticle, and show segmental defects in lateral epidermis or dorsal and lateral epidermis. Defects are evident in the neurectoderm, Malpighian tubules, optic lobe precursor, PNS and SNS. In germ-line clones, no eggs are recovered.
The principal midgut epithelial cells spread over the visceral mesoderm but do not become columnar, they maintain a rounded to cuboidal shape, and do not form a monolayer. At later stages (stage 14-17) the principle midgut epithelial cells become attached to the visceral mesoderm and gradually adopt a more wild type appearance. By the time the embryos are fully differentiated, no difference from wild type can be seen.