Endocrine Abstracts

Background: Defective thyroid gland development occurs in 80% of congenital hypothyroidism (incidence of 1:3000–1:4000). Only <5% have been shown to be caused by molecular genetic defects in few transcription factor genes (Nkx2.1, Nkx2.5, Foxe1, Pax8, Hhex) which are known to play a role in thyroid gland development. Therefore, other genes with a critical role in early thyroid development are likely to be involved in the pathogenesis of thyroid dysgenesis.

Methods: We screened a whole-mount in situ-hybridization database for positive signals in thyroid precursor cells. This database contains the amount of about 3000 different gene probes hybridized on whole mouse embryos aged 9.5 days (E9.5). Positive probes where re- hybridized on histological slices of E 9.5 as well as E10.5, E11.5, E12.5, and E15.5. As a second method, RNA was isolated of thyroid precursor cells of 9.5 days old mouse embryos collected by lasermicrodissection. RT-PCR and sequencing was performed.

Results: Out of 10 positive patterns, we could prove expression in thyroid precursors of 1 gene using slice hybridization. We got positive signals in thyroid precursors at stage E9.5, E12.5, E15.5. We got negative signals at stage E10.5, E11.5. This was validated by RT-PCR. A PCR product of cDNA of E9.5 thyroid precursors could be amplified and sequenced. A PCR product of surrounding tissue was also amplified, but showed a different size. There was one exon missing in the sequence of this PCR product.

Conclusion: We identified a new gene not known so far to be expressed in thyroid precursor cells. The pattern of appearance at stage E 9.5, disappearance at E10.5 and E11.5 and reappearence at E12.5 has not been described for another gene before. This may suggest a special role of the gene and its transcript in different stages of thyroid development. Furthermore the different sizes of the PCR-products (thyroid and surrounding tissue) points to the presents of thyroid precusor specific splice-variants.