Toward an Understanding of Thyroid Hormone Activity in the Development of Chick Corneal Transparency
Major
Neuroscience
Submission Type
Oral Presentation
Area of Study or Work
Biochemistry, Neuroscience
Faculty Advisor
Tyler Schwend
Location
CNS E101
Start Date
4-12-2025 11:15 AM
End Date
4-12-2025 12:15 PM
Abstract
Title: Toward an Understanding of Thyroid Hormone Activity in the Development of Chick Corneal Transparency Authors: Jishnu Satheeshreddy1, Tyler Schwend1,2 1 Department of Neuroscience, Illinois Wesleyan University, Bloomington, IL 61761 2 Department of Biology, Illinois Wesleyan University, Bloomington, IL 61761 Purpose: Clear vision depends on proper light transmittance through a transparent cornea. Embryonic chick corneas begin as an opaque tissue that becomes progressively transparent throughout the second half of embryonic development (E10-E20) before reaching maximum pre-hatching transparency at E20. Although previous work showed that the development of corneal transparency in the chick can be accelerated or delayed by modulating embryonic thyroid hormone levels, whether the cornea relies on endogenous TH to achieve maximum pre-hatching transparency is unclear. Moreover, details underlying the stimulatory effect of TH on cornea transparency are poorly understood. Methods: Eggs were injected at various developmental timepoints, spanning E6-E11, with thyroid hormones (T4 or T3) to obtain hyperthyroid chick embryos, or with thiouracil (2TU) to obtain hypothyroid chick embryos. E10-E19 corneas were harvested. Corneal transparency was measured digitally on whole-dissected corneas or mRNA expressions were quantified by reverse transcriptase (RT)-PCR using cDNA obtained from corneal cells. Results: Our studies reveal that TH activity is necessary within a narrow developmental window, between E6-E11, for the cornea to reach full transparency. In controls, the E11 cornea is 60% transparent and progressively clears by 5-10% daily before achieving 95% transparency by E19. Surprisingly, we found that TH activity is dispensable for the earliest stages of corneal transparency, as 2TU-treated corneas display corneal clearing from 60-75% in an identical fashion to controls. However, 2TU-treated corneas become permanently and irreversibly paused at 75%, indicating that later stages of corneal transparency progression rely on TH activity. Molecular and cellular analysis of 2TU-treated corneas is underway to determine the precise mechanisms that underpin the requirement of TH activity on development of corneal transparency. Conclusions: TH activity is necessary for chick corneas to reach maximum pre-hatching transparency and obtain clear vision upon hatching.
Toward an Understanding of Thyroid Hormone Activity in the Development of Chick Corneal Transparency
CNS E101
Title: Toward an Understanding of Thyroid Hormone Activity in the Development of Chick Corneal Transparency Authors: Jishnu Satheeshreddy1, Tyler Schwend1,2 1 Department of Neuroscience, Illinois Wesleyan University, Bloomington, IL 61761 2 Department of Biology, Illinois Wesleyan University, Bloomington, IL 61761 Purpose: Clear vision depends on proper light transmittance through a transparent cornea. Embryonic chick corneas begin as an opaque tissue that becomes progressively transparent throughout the second half of embryonic development (E10-E20) before reaching maximum pre-hatching transparency at E20. Although previous work showed that the development of corneal transparency in the chick can be accelerated or delayed by modulating embryonic thyroid hormone levels, whether the cornea relies on endogenous TH to achieve maximum pre-hatching transparency is unclear. Moreover, details underlying the stimulatory effect of TH on cornea transparency are poorly understood. Methods: Eggs were injected at various developmental timepoints, spanning E6-E11, with thyroid hormones (T4 or T3) to obtain hyperthyroid chick embryos, or with thiouracil (2TU) to obtain hypothyroid chick embryos. E10-E19 corneas were harvested. Corneal transparency was measured digitally on whole-dissected corneas or mRNA expressions were quantified by reverse transcriptase (RT)-PCR using cDNA obtained from corneal cells. Results: Our studies reveal that TH activity is necessary within a narrow developmental window, between E6-E11, for the cornea to reach full transparency. In controls, the E11 cornea is 60% transparent and progressively clears by 5-10% daily before achieving 95% transparency by E19. Surprisingly, we found that TH activity is dispensable for the earliest stages of corneal transparency, as 2TU-treated corneas display corneal clearing from 60-75% in an identical fashion to controls. However, 2TU-treated corneas become permanently and irreversibly paused at 75%, indicating that later stages of corneal transparency progression rely on TH activity. Molecular and cellular analysis of 2TU-treated corneas is underway to determine the precise mechanisms that underpin the requirement of TH activity on development of corneal transparency. Conclusions: TH activity is necessary for chick corneas to reach maximum pre-hatching transparency and obtain clear vision upon hatching.