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Two UV-sensitive targets in dorsoanterior specification of frog embryos
1Department of Zoology, University of Toronto, Ontario, Canada.
Abstract:
Previous work has shown that ultraviolet (UV) irradiation of fertilized frog eggs yields embryos that lack dorsal and anterior structures. The eggs fail to undergo the cortical/cytoplasmic rotation that specifies dorsoventral polarity, and they lack an array of parallel microtubules associated with the rotation. These eggs can be rescued by tilting with respect to gravity, and normal dorsoanterior development occurs. We find here that UV irradiation of Xenopus prophase I oocytes or Rana metaphase I oocytes also causes the dorsoanterior deficient syndrome, but the UV target is different from that in fertilized eggs. Tilting eggs, irradiated as oocytes, with respect to gravity, does not rescue dorsoanterior development, although lithium treatment does. The UV dose required to produce dorsoanterior deficiency for Rana metaphase I oocytes is much less than that for fertilized eggs, and the oocytes can form the array of parallel microtubules and undergo the cortical/cytoplasmic rotation after fertilization. Despite these features of normal development, no dorsoanterior structures form. While the UV target in fertilized eggs is thought to be the parallel microtubules (Elinson & Rowning, 1988; Devl Biol. 128, 185-197), the UV target in the oocytes may be a dorsal determinant.
Insights
Ultraviolet (UV) irradiation of frog oocytes, unlike fertilized eggs, causes developmental defects by targeting a dorsal determinant, not microtubules. Tilting rescues eggs but not oocytes, though lithium treatment is effective.
Area of Science:
- Developmental Biology
- Cell Biology
- Xenopus and Rana embryology
Background:
- Fertilized frog eggs irradiated with UV light exhibit defects in dorsal and anterior structure formation.
- This UV-induced syndrome is linked to the failure of cortical/cytoplasmic rotation, essential for establishing dorsoventral polarity.
- The parallel microtubules, crucial for this rotation, are hypothesized as the UV target in fertilized eggs.
Purpose of the Study:
- To investigate the UV target responsible for the dorsoanterior deficient syndrome in frog oocytes.
- To compare the UV sensitivity and developmental rescue mechanisms between irradiated oocytes and fertilized eggs.
- To identify potential differences in UV targets affecting early embryonic development.
Main Methods:
- UV irradiation of Xenopus prophase I oocytes and Rana metaphase I oocytes.
- Assessment of embryonic development following UV irradiation and subsequent fertilization.
- Experimental rescue attempts using gravitational tilting and lithium treatment.
Main Results:
- UV irradiation of oocytes, similar to fertilized eggs, induced the dorsoanterior deficient syndrome.
- However, tilting failed to rescue oocytes irradiated as oocytes, unlike fertilized eggs.
- Lithium treatment successfully rescued oocytes irradiated as oocytes.
- UV-sensitive targets in oocytes appear different from those in fertilized eggs, potentially involving a dorsal determinant rather than microtubules.
Conclusions:
- The UV-sensitive target during oocyte maturation differs from that in fertilized eggs.
- Gravitational tilting is ineffective for rescuing UV-irradiated oocytes, suggesting a distinct developmental pathway disruption.
- Lithium treatment offers a potential rescue strategy for UV-induced defects originating at the oocyte stage, highlighting a novel dorsal determinant.