Thyroxine Affects Expression of KSPG-Related Genes, the Carbonic Anhydrase II Gene, and KS Sulfation in the Embryonic Chicken Cornea

Abstract

Thyroxine modifies expressions of KSPG synthesis and carbonic anhydrase genes.

Thyroxine Increases the Rate but Does Not Alter the Pattern of Innervation during Embryonic Chick Corneal Development

“…When precociously administered to the embryo at high levels, T4 increases corneal thinning and transparency. 16,17,19 Similarly, precocious administration of T4 on E8 increased the rate of nerve penetration into the cornea by E11, such that nerves covered a greater proportion of the cornea in T4-treated embryos than in control embryos (Fig. 5).…”

“…19 In contrast, E8 treatment of embryos with T4 did not alter corneal expressions of genes for the neurotrophins that stimulate NCderived TG axon growth, NGFB, NTF3, or BDNF; of their receptors, TRK1, -2, or -3 or NGFR; of the Schwann cell marker genes MPZ or GFAP; or of the Schwann cell neurotrophin gene NRG1 isoforms 1a or 2b (Fig. 9).…”

“…Eggs injected with T4 or SalG alone were handled as described previously, 19 except that the eggs were injected on E8. For injections of T4ϩ2-TU or 2-TU alone, the eggs were turned on their sides on E8, a small piece of egg shell plus inner shell membrane was removed, and solutions were deposited onto the chorioallantoic membrane.…”

“…19 Sequences of genes of interest were obtained from GenBank (http://www.ncbi.nlm.nih.gov/Genbank; provided in the public domain by the National Center for Biotechnology Information, Bethesda, MD). PCR primers for real-time PCR were designed using software (Designer 31 Molecular Beacons Design; Sigma-Aldrich, St. Louis, MO) to amplify fragments between 80 and 150 base pairs in length, and are listed in Table 1.…”

“…In contrast, corneal thinning is prevented by in ovo treatment with 2-thiouracil (2-TU). We recently showed that precocious T4 treatment of chick embryos increases corneal expressions of mRNAs for nuclear thyroxine hormone receptor beta and carbonic anhydrase II, an enzyme that generates bicarbonate ions, 19 suggesting that generation and movement of bicarbonate ions may regulate corneal hydration and transparency, and thus that increasing concentrations of T4/T3 in the eye may contribute to normal transparency development in the avian eye. Observations of early nerve exclusion from the cornea suggest that nerve growth cone-repulsive signals are released from the early developing cornea and that at a critical time something changes in the cornea that either terminates the nonpermissive signals or overrides them with nerve growth cone permissive signals.…”