Pathway to a phenocopy: Heat stress effects in early embryogenesis.
BACKGROUND
Heat shocks applied at the onset of gastrulation in early Drosophila embryos frequently lead to phenocopies of U-shaped mutants-having characteristic failures in the late morphogenetic processes of germband retraction and dorsal closure. The pathway from nonspecific heat stress to phenocopied abnormalities is unknown.


RESULTS
Drosophila embryos subjected to 30-min, 38 °C heat shocks at gastrulation appear to recover and restart morphogenesis. Post-heat-shock development appears normal, albeit slower, until a large fraction of embryos develop amnioserosa holes (diameters > 100 µm). These holes are positively correlated with terminal U-shaped phenocopies. They initiate between amnioserosa cells and open over tens of minutes by evading normal wound healing responses. They are not caused by tissue-wide increases in mechanical stress or decreases in cell-cell adhesion, but instead appear to initiate from isolated apoptosis of amnioserosa cells.


CONCLUSIONS
The pathway from heat shock to U-shaped phenocopies involves the opening of one or more large holes in the amnioserosa that compromise its structural integrity and lead to failures in morphogenetic processes that rely on amnioserosa-generated tensile forces. The proposed mechanism by which heat shock leads to hole initiation and expansion is heterochonicity, i.e., disruption of morphogenetic coordination between embryonic and extra-embryonic cell types.
Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee.
Sarah M
SM
Crews
Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee.
W Tyler
WT
McCleery
Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee.|Vanderbilt Institute for Integrative Biosystem Research and Education, Vanderbilt University, Nashville, Tennessee.
M Shane
MS
Hutson
D000818:Animals; D004331:Drosophila melanogaster; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000196:embryology*; D054262:Gastrulation; D018869:Heat-Shock Response
Drosophila; amnioserosa; apoptosis; delamination; developmental defect; epithelium; extraembryonic tissue; extrusion; heat shock; heterochronicity; phenocopy