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Egg timers: how is developmental time measured in the early vertebrate embryo?
Author(s) -
Johnson Martin H.,
Day Margot L.
Publication year - 2000
Publication title -
bioessays
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.175
H-Index - 184
eISSN - 1521-1878
pISSN - 0265-9247
DOI - 10.1002/(sici)1521-1878(200001)22:1<57::aid-bies10>3.0.co;2-l
Subject(s) - hourglass , vertebrate , embryo , biology , biological clock , evolutionary biology , neuroscience , circadian rhythm , microbiology and biotechnology , genetics , physics , astronomy , gene
Eggs and early embryos appear to be programmed to undertake particular developmental decisions at characteristic times, although precisely how these decisions are timed is unknown. We discuss the possible roles and interactions during early vertebrate development of two broad categories of timers: 1) those that involve cyclic or sequential mechanisms, referred to as clocks; and 2) those that require an increase or decrease in some factor to a threshold level for progression of time, referred to as hourglass timers. It is concluded that both clock‐like timers linked to various features of the cell cycle and hourglass timers are involved in early developmental timing. The possible involvement of elements of circadian clock timers is also considered. BioEssays 22:57–63, 2000. ©2000 John Wiley & Sons, Inc.