PREFIX sx: <http://www.w3.org/ns/shex#>

<http://schema.example/IssueShape> a sx:ShapeDecl ; sx:shapeExpr [ a sx:Shape;
   sx:expression [
     a sx:TripleConstraint;
     sx:max -1;
     sx:min 0;
     sx:predicate <http://schema.example/related>;
     sx:valueExpr <http://schema.example/IssueShape>
   ] ] .

[]
     a sx:Schema;
     sx:shapes (<http://schema.example/IssueShape>) .