autoprocessing thus is associated with tethering of the amino terminal signaling domain to the cell surface amino terminal domain protein derived by processing of the hh precursor is designated hh np to distinguish it from amino terminal domain derived from a truncated construct hh n as would be expected for a potent secreted signal whose expression is spatially restricted within segments autoprocessing and cell surface tethering play an important role in segmental patterning porter et al 1996a this role was revealed by comparing the effects of localized expression of hh n or hh np in transgenic drosophila embryos when activated at the normal sites of hh transcription transgenes expressing hh np which is also the form of the endogenous protein signal showed no significant alterations in the normal segmental patterns of gene expression or cuticle formation in contrast similar localized expression of transgenic hh n caused disruption of segmental patterning equivalent to that caused by ubiquitous high level expression of hh protein autoprocessing thus appears to restrict the spatial distribution of hh signaling activity and immunofluorescence studies indeed confirm that hh n more readily diffuses from expressing cells to surrounding cells than does hh np porter et al 1996a these immunofluorescence studies also revealed a difference in subcellular localization within expressing cells with hh np sequestered in large punctate structures in basolateral domains of epidermal cells hh n protein from the truncated construct in contrast lacks this type.