Smallminded was isolated in a screen of GAL4 enhancer-trap lines designed to identify those genes in which reporter gene expression is restricted to sensory neurons. In addition to a neural expression pattern , this line also has a mutant phenotype associated with the insert. Larvae homozygous for the insertion hatch normally but exhibit poor locomotion and become developmentally arrested as second instar larvae. Homozygous larvae can survive as second instar larvae for up to 8 weeks without further development before dying. Abnormal levels of cell death by apoptosis occur in smid mutants.
Apoptosis is accompanied by heightened expression of reaper and head involution defective .
Several yeast and mammalian proteins related to Smid have a demonstrable role in the cell cycle. More closely related to Smallminded than the proteins described above is the C. elegans protein MAC-1. A MAC-1 transgene under the control of a heat shock promoter prevents some natural cell deaths in C. elegans . These mature animals show additional defects, such as the formation of vacuoles in the intestine, and abnormal vulval and gonadal development. It is not known if these problems reflect a widespread requirement for mac-1 in larval development, or are a side effect of slowed development.