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J. Cell Biol.,
Volume 141, Number 4, May 18, 1998 1073-1081
Wellcome/CRC Institute, Cambridge CB2 1QR, England; and Department of Biochemistry, Cambridge University, Cambridge
CB2 1QW, England
Cells can vary their adhesive properties by
modulating the affinity of integrin receptors. The activation and inactivation of integrins by inside-out mechanisms acting on the cytoplasmic domains of the integrin subunits has been demonstrated in platelets, lymphocytes, and keratinocytes. We show that in the
embryo, normal morphogenesis requires the 
subunit
cytoplasmic domain to control integrin adhesion at the
right times and places. PS2 integrin (PS2
PS) adhesion
is normally restricted to the muscle termini, where it is
required for attaching the muscles to the ends of other
muscles and to specialized epidermal cells. Replacing
the wild-type PS2 with mutant forms containing cytoplasmic domain deletions results in the rescue of the
majority of defects associated with the absence of the
PS2 subunit, however, the mutant PS2 integrins are excessively active. Muscles containing these mutant integrins make extra muscle attachments at aberrant positions on the muscle surface, disrupting the muscle
pattern and causing embryonic lethality. A gain-
of-function phenotype is not observed in the visceral
mesoderm, showing that regulation of integrin activity
is tissue-specific. These results suggest that the PS2 subunit cytoplasmic domain is required for inside-out
regulation of integrin affinity, as has been seen with the
integrin IIb3.
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