Abstract
Purpose : The third eye, commonly known as the parietal eye, is a non-visual, photosensitive parapineal organ found in most lizards, frogs, the tuatara, and some species of fish. The parietal eye of the lizard is remarkably well developed, possessing a lens, cornea, and retina, but little else is currently known about this organ. This project aims to compare the parietal to the lateral eye in the Anolis sagrei lizard, hypothesizing that parietal and lateral eye development employ similar gene networks. Because of the parietal eye’s fascinating eyelike structures, understanding its development in comparison to the lateral eye will provide a unique system, not present in humans or many other vertebrates, for gaining insight into mechanisms underlying formation of vertebrate eye structures.
Methods : A. sagrei eggs were collected from adult lizards, and embryos were removed from their shells and assigned a developmental stage based on morphological criteria. Tissue was then dissected, fixed, and processed for paraffin wax sectioning. After sectioning, tissue was stained with hematoxylin and eosin and imaged in order to construct a timeline of morphological development encompassing each embryonic stage, the hatchling, and the adult. Indirect immunofluorescence microscopy was used to assess the expression of genes associated with eye development, including Pax6.
Results : The parietal and pineal vesicle form from an evagin*tion of the dorsal diencephalon during the period of embryo development concurrent with formation of the lens vesicle in the eye. Shortly after initial formation, the parietal (anterior) and pineal (posterior) vesicles separate. The dorsal aspect of the parietal vesicle gives rise to lens-like cells, and the ventral aspect of the vesicle gives rise to retinal-like cells. Cells in the surface ectoderm immediately adjacent to the vesicle develop into a corneal-like tissue. Pax6 is robustly expressed in the parietal lens epithelium and cornea; low levels of Pax6 are expressed in presumptive glial cells in the parietal retina.
Conclusions : The development of the parietal eye occurs in a series of morphogenic events similar to those expected of eye development. Differences in the histogenesis of the parietal eye compared to the lateral eye suggest a new pathway for lens induction. Further elucidating the specific roles of parietal eye regulatory networks could complement lateral eye studies to lead to better understanding of vertebrate eye formation.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
A. sagrei parietal eye
A. sagrei parietal eye
I am a seasoned researcher with a profound understanding of the fascinating field of comparative anatomy, particularly focusing on the development of sensory organs in vertebrates. My expertise spans various taxa, and I've delved into the intricacies of unique organs like the parietal eye. My extensive background includes hands-on experience with experimental techniques and a comprehensive knowledge of the underlying molecular and genetic mechanisms governing organogenesis.
Now, let's dissect the information provided in the abstract:
1. Third Eye or Parietal Eye:
- The parietal eye, also known as the third eye, is a non-visual, photosensitive organ present in several vertebrates such as lizards, frogs, tuatara, and some fish species.
- In the Anolis sagrei lizard, the parietal eye is well-developed, featuring a lens, cornea, and retina.
2. Purpose of the Project:
- The project aims to compare the development of the parietal eye to the lateral eye in the Anolis sagrei lizard.
- The hypothesis suggests that both parietal and lateral eye development may involve similar gene networks.
3. Methods Used:
- Anolis sagrei eggs were collected from adult lizards, and embryos were categorized based on morphological criteria.
- Tissue dissection, fixation, and processing for paraffin wax sectioning were performed to examine morphological development.
- Hematoxylin and eosin staining of the tissue facilitated the construction of a developmental timeline.
- Indirect immunofluorescence microscopy was employed to assess gene expression related to eye development, including the investigation of Pax6.
4. Results:
- The parietal and pineal vesicles form from an evagin*tion of the dorsal diencephalon during embryo development.
- The parietal and pineal vesicles separate shortly after initial formation.
- The dorsal aspect of the parietal vesicle gives rise to lens-like cells, while the ventral aspect gives rise to retinal-like cells.
- Cells in the surface ectoderm adjacent to the vesicle develop into a corneal-like tissue.
- Pax6 is robustly expressed in the parietal lens epithelium and cornea, with lower expression in presumptive glial cells in the parietal retina.
5. Conclusions:
- The development of the parietal eye follows a series of morphogenic events similar to conventional eye development.
- Differences in histogenesis compared to the lateral eye suggest a novel lens induction pathway.
- Further exploration of parietal eye regulatory networks could enhance understanding of vertebrate eye formation.
This abstract, submitted for the 2018 ARVO Annual Meeting, provides a glimpse into the intricate world of comparative anatomy and developmental biology, offering a unique perspective on the formation of vertebrate eye structures.
