JUVENILE-HORMONE EFFECT ON DNA-SYNTHESIS AND APOPTOSIS IN CASTE-SPECIFIC DIFFERENTIATION OF THE LARVAL HONEY-BEE (APIS-MELLIFERA L.) OVARY

Caste-specific differentiation of the honey bee ovary commences in the last larval instar. In this process, formation of germ cell clusters by synchronous and incomplete mitoses occurs in the queen ovary, where as in the worker ovary programmed cell death is the dominant feature. BrdU and TUNEL labeling were used to study dynamics of cell proliferat ion and apoptosis-dependent DNA degradation in ovaries of naturally de veloping queens and workers, as well as in juvenile hormone-treated wo rker larvae. Cell proliferation in ovaries of last-instar queen larvae generally exceeded that in workers, except for the late feeding phase . This inversion in cell proliferation patterns coincided with the ons et of apoptosis in worker ovaries, as evidenced by TUNEL labeling. Juv enile hormone application to early-fifth-instar worker larvae had two noticeable effects. First, it diminished the number of S-phase nuclei in ovaries of late feeding-phase workers, bringing them to queen-like levels. Second, it prevented the induction of apoptotic DNA degradatio n. Caste-specific regulation of cell division in connection with progr ammed cell death can thus be attributed to the previously described di fferences in juvenile hormone titer in queen and worker larvae, adding a new facet to this hormone's multiple functions. (C) 1998 Elsevier S cience Ltd. All rights reserved.