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alternative genetic programs. The perception of daylight duration and aver-
age temperature are potential reliable cues for an organism to perceive sea-
sonal time and to induce diapause and/or modifications of larval/pupal
growth. Is the endogenous circadian clock pivotal in mediating the hor-
monal sensitivity to light changes or is the visual system the primary medi-
ator, or do both play a role? Insights from
B. mori
, which exhibits a strong
photoperiodic sensitivity in specifying developmental fate, during early lar-
val life, the DH-based diapause trajectory will provide a good model to study
the regulatory mechanism upstream of developmental hormones. What role
and by what mechanism could changes in average temperature be perceived
with time is also an important issue to explore?
As described, diapause is also triggered in the vertebrate killifish embryo
by a mechanism that, presumably, is hormonally based, as is the IGF-1-based
block in development of zebrafish embryos under certain conditions.
A functional analysis of IGF-1 signaling in both zebrafish and killifish
embryos, together with engineering of cryoprotecting potential, may pro-
vide a framework for deciphering how hibernal diapause evolved in verte-
brates within a preexisting developmental program.
ACKNOWLEDGMENTS
L.S. is supported by a doctoral fellowship from the University of Padova (Italy). L.S. also
thanks Fondazione Ing. “A.Gini” of University of Padova (Italy) and Rudi Costa
(University of Padova). M.B.O. is supported by NIH grant GM R01 GM0933001. The
authors thank Emilie Snell-Rood for helpful comments on the manuscript.
REFERENCES
