Null mutations in the alpha PS2 and beta PS integrin subunit genes have distinct phenotypes

The researchers used genetic analysis to compare the effects of null mutations in alpha PS2 and beta PS subunit genes. They isolated three new alleles of the inflated gene, each with a molecular lesion in the alpha PS2 gene. These alleles were tested for their ability to cause loss of if activity. A 39 kb genomic fragment containing the alpha PS2 gene was introduced into the germline via P-element-mediated transformation. This fragment was used to rescue if mutations, confirming that alpha PS2 encodes the inflated gene. The study compared the phenotypes of inflated and myospheroid mutants. Embryos were examined for adhesion defects between muscles and epidermis. The analysis focused on the dorsal midline and other attachment sites to assess integrin function.

The study found that alpha PS2 is encoded by the inflated gene. Three new if alleles were isolated, each with a molecular lesion in alpha PS2 and complete loss of if activity. A 39 kb genomic fragment rescued if mutations, confirming the gene's identity. The null phenotype of inflated mutants was compared with that of myospheroid mutants. Beta PS subunit was required for epidermal adhesion along the dorsal midline. In contrast, alpha PS2 subunit was not required for this adhesion. In inflated mutants, muscles remained attached to other cell layers longer than in myospheroid mutants. This suggests that alpha PS2 beta PS integrin contributes only partially to adhesion. The findings rule out a model where PS integrin function occurs solely through direct interaction. Instead, the data support a model where integrins work in part through extracellular matrix interactions.

The study concludes that alpha PS2 and beta PS integrin subunits have distinct roles in adhesion. The beta PS subunit is essential for epidermal adhesion along the dorsal midline. The alpha PS2 subunit is not required for this specific adhesion. In inflated mutants, muscles remain attached longer than in myospheroid mutants. This indicates that alpha PS2 beta PS integrin contributes only part of the adhesive activity. The findings rule out a model where PS integrin function occurs solely through direct interaction. Instead, the data support a model involving extracellular matrix interactions. The results suggest that PS integrins function in part through indirect mechanisms. The study provides evidence that different integrin subunits have distinct roles in adhesion.