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Introduction: Sea urchin embryos exhibit radial holoblastic cleavage in which the first and second cleavages are both meridional and perpendicular to each other. The third cleavage is equatorial, and the fourth cleavage divides unequally to produce mesomeres, macromeres, and micromeres (Gilbert, 2003). These cleavage patterns are well understood on a group level, but it is not completely clear how the individual cells are regulated on a molecular level. One can follow the egg from fertilization to blastula to gastrula to pluteus larvae formation, but this is usually performed under ideal situations. If the conditions change, such as the salt concentration or temperature of the water, how will this affect the development of the sea urchin? Many processes, acting in
sequence or in parallel, make up the cell cycle. Many
studies have shown how the cell cycle is regulated at the
molecular level in the cyclic accumulation and destruction
of cyclins and the cyclic activity of M phase-promoting
factor (Meijer et al., 1991). However, only some of these
processes affect the length of the cycle (Nurse, 1990).
Other environmental factors have been suggested as
additional regulators of the cell cycle. For example,
temperature has been shown to have a number of effects on
the role of various phases of mitotic division, such as the
rate of oxygen consumption and carbon dioxide production
(Hoadley, 1937). Researchers have found that cell cycle
events differ greatly in their degree of temperature
dependence. Sea urchins are one organism that is affected by
temperature. A temperature- dependent period exists after
egg fertilization in which the duration of the cleavage
cycle and normal development patterns are affected by the
temperature of the surrounding environment (Yamada, K, and
K. Mihashi, 1998). |
