An 11-ketotestosterone induced kidney-secreted protein:: the nest building glue from male three-spined stickleback, Gasterosteus aculeatus

In male three-spined sticklebacks, Gasterosteus aculeatus, the kidney hypertrophies during the breeding season and produces a glue which is used in nest-building. This hypertrophy is androgen dependent with 11-ketotestosterone (II KT) being most effective. The aim of the present study was to characterize the protein composition of this glue. Threads of glue were collected from stickleback nests and glue material was sampled from the content of urinary bladders of male sticklebacks in breeding condition. The samples were investigated using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). One major glycoprotein dominated in both the nest-threads and urinary bladder samples. The identified glycoprotein had a molecular mass of approximately 203 kDa. After deglycosylation the molecular mass was approximately 200 IrDa. The amino acid composition of the protein from urinary bladder content was almost identical to the amino acid composition of the protein from the nest-threads. The protein had a relatively high content of cysteine (7.6-8.0%). The glycoprotein was named spiggin. Spiggin was absent in the urinary bladder of untreated castrated fish, but spiggin was present in sham-operated fish and in castrated fish treated with 11 KT. These results demonstrate that spiggin is induced by II KT. Spiggin is so far the only protein known to be induced by 11KT and based on the present findings we suggest that spiggin represents a novel structural protein.