Description
The vertebrate eye originates from a single forebrain-derived eye field, which splits into two optic vesicles during evagination. While this process is generally assumed to generate bilaterally symmetric structures, it remains unclear whether symmetry is established during this initial evagination or is subsequently rectified.
To address this, we used zebrafish as a vertebrate model because their external and transparent embryonic development enables direct observation of early eye morphogenesis. We quantified eye volume in zebrafish using transgenic lines expressing fluorescent proteins in the developing eye. Embryos were imaged using confocal microscopy, and eye volumes were reconstructed in three dimensions using Imaris. This allowed direct comparison of paired eye volumes within individual embryos. Size difference between left and right eyes were quantified as the normalized relative difference between paired eye volumes in individual embryos.
Our data suggest that measurable left–right size asymmetries are present at early developmental stages. Notably, size asymmetries are progressively reduced over time, suggesting that compensatory growth mechanisms that enable bilateral symmetry during eye development.
This study establishes a quantitative framework for assessing bilateral symmetry and provides initial evidence that organ size is actively regulated to ensure symmetry during development. Future work will extend this approach to eye-development mutants with a smaller eye field. This will allow us to test whether developmental perturbations increase left–right eye size asymmetry or impair the ability of compensatory growth to enable bilateral symmetry. Together, this work provides a quantitative framework for understanding how bilateral symmetry is dynamically achieved during organogenesis.
Lay Abstract
During early development, the two eyes emerge from a single group of cells in the developing brain. Although the two eyes usually end up similar in size, it is not clear whether they are already perfectly matched from the beginning, or whether small early differences are corrected later as the embryo grows.
In this project, we used zebrafish embryos to study how eye symmetry develops. Zebrafish are particularly useful because their embryos develop outside the mother’s body and are transparent, allowing early eye formation to be directly observed. We used fluorescent markers that label the developing eye, took three-dimensional microscope images, and measured the volume of the left and right eyes in the same embryo. This allowed us to compare the two eyes directly and calculate how different they were in size.
Our early results suggest that the left and right eyes show measurable size differences at early stages of development. These differences become corrected over time, suggesting that developing embryos may adjust growth to make both eyes develop a similar size.
Our work helps us understand how organs develop into balanced left–right pairs, and may provide a useful way to study what happens when normal eye development is disrupted.
| Lay Title | How do the two eyes grow to the same size during development? |
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| Role | Master Student |