Synthesis and transport of storage proteins by testes in Heliothis virescens

The synthesis of two storage protein subunits, 76,000-Mr and 82,000-Mr polypeptides, by the testes sheath has been studied in Heliothis virescens. Like fat body, which is the primary site of synthesis for the large extratesticular pool, cells of the testes sheath secrete glycosylated storage proteins assembled into hexamers. The testis sheath differed from fat body in several important respects, including the failure to synthesize an abundant (in the hemolymph) 74,000-Mr storage protein, its relatively reduced expression of the 76,000-Mr polypeptide, and the absence of resorption of storage proteins from the lumen of the testis during pupal development. Cyst cells were also shown to import actively the 82,000-Mr storage protein by pinocytosis of testicular fluid and transfer it to the developing spermatids. Unlike other cell types that sequester storage proteins in the form of cytoplasmic granules, their localization within spermatids was exclusively mitochondrial. These observations suggest that expression of the storage protein genes is regulated tissue specifically and reveal novel pathways for their transport and, perhaps, utilization and function during development.