The Optx2 homeobox gene is expressed in early precursors of the eye and activates retina-specific genes

Vertebrate eye development begins at the gastrula stage, when a region known as the eye field acquires the capacity to generate retina and lens. Optx2, a homeobox gene of the sine oculis-Six family, is selectively expressed in this early eye field and later in the lens placode and optic vesicle. The distal and ventral portion of the optic vesicle are fated to become the retina and optic nerve, whereas the dorsal portion eventually loses its neural characteristics and activates the synthesis of melanin, forming the retinal pigment epithelium. Optx2 expression is turned off in the future pigment epithelium but remains expressed in the proliferating neuroblasts and differentiating cells of the neural retina. When an Optx2-expressing plasmid is transfected into embryonic or mature chicken pigment epithelial cells, these cells adopt a neuronal morphology and express markers characteristic of developing neural retina and photoreceptors. One explanation of these results is that Optx2 functions as a determinant of retinal precursors and that it has induced the transdifferentiation of pigment epithelium into retinal neurons and photoreceptors. We also have isolated optix, a Drosophila gene that is the closest insect homologue of Optx2 and Six3. Optix is expressed during early development of the fly head and eye primordia.

A family of genes required for maintenance of cell wall integrity and for the stress response in Saccharomyces cerevisiae

The PKC1–MPK1 pathway in yeast functions in the maintenance of cell wall integrity and in the stress response. We have identified a family of genes that are putative regulators of this pathway. WSC1, WSC2, and WSC3 encode predicted integral membrane proteins with a conserved cysteine motif and a WSC1–green fluorescence protein fusion protein localizes to the plasma membrane. Deletion of WSC results in phenotypes similar to mutants in the PKC1–MPK1 pathway and an increase in the activity of MPK1 upon a mild heat treatment is impaired in a wscΔ mutant. Genetic analysis places the function of WSC upstream of PKC1, suggesting that they play a role in its activation. We also find a genetic interaction between WSC and the RAS–cAMP pathway. The RAS–cAMP pathway is required for cell cycle progression and for the heat shock response. Overexpression of WSC suppresses the heat shock sensitivity of a strain in which RAS is hyperactivated and the heat shock sensitivity of a wscΔ strain is rescued by deletion of RAS2. The functional characteristics and cellular localization of WSC suggest that they may mediate intracellular responses to environmental stress in yeast.