CIRCADIAN-RHYTHM OF SPERM RELEASE IN THE GYPSY-MOTH, LYMANTRIA-DISPAR- ULTRASTRUCTURAL-STUDY OF TRANSEPITHELIAL PENETRATION OF SPERM BUNDLES

Release of mature bundles of spermatozoa from the testis into the vas deferens is a critical but poorly understood step in male insect repro duction. In moths, the release of sperm bundles is controlled by a cir cadian clock which imposes a temporal gate on the daily exit of bundle s through the terminal epithelium-a layer of specialized epithelial ce lls separating testis follicles from the vas deferens. The sequence of cellular events associated with the daily cycle of sperm release was investigated by scanning and transmission electron microscopy. In the hours preceding sperm release, there is a solid barrier between the te stis and the vas deferens formed by the interdigitation of cytoplasmic processes of adjacent terminal epithelial cells. At the beginning of the sperm release cycle, sperm bundles protrude through this barrier w hile the terminal epithelial cells change their shape and position rel ative to the bundles. Subsequently, the cyst cells enveloping the sper m bundles break down and spermatozoa move out of the testis through th e exit channels formed between the epithelial cells. Afterwards, cyst cell remnants land other cellular debris are released into the vas def erens lumen, and the epithelial barrier is reconstructed due to phagoc ytic activity of its cells. These data provide a foundation on which t o build an understanding of the cellular mechanisms of clock-controlle d sperm release in insects. (C) 1997 Elsevier Science Ltd. All rights reserved.