Juvenile hormone effect on DNA synthesis and apoptosis in caste-specific differentiation of the larval honey bee (Apis mellifera L.) ovary

Abstract

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, whereas in the worker ovary programmed cell death is the dominant feature. BrdU and TUNEL labeling were used to study dynamics of cell proliferation and apoptosis-dependent DNA degradation in ovaries of naturally developing queens and workers, as well as in juvenile hormone-treated worker 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 onset of apoptosis in worker ovaries, as evidenced by TUNEL labeling. Juvenile 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 degradation. Caste-specific regulation of cell division in connection with programmed cell death can thus be attributed to the previously described differences in juvenile hormone titer in queen and worker larvae, adding a new facet to this hormone's multiple functions.