Characterization of the mouse transforming growth factor gene: Its expression during eyelid development and in waved 1 tissues

The spontaneous mouse waved 1 (wa1) mutation is allelic with the transforming growth factor α (TGF-α) gene and produces phenotypes similar to those of TGF-α knockout mice. Here, we show that TGF-α mRNA and protein levels are measurable in wa1 tissues but reduced 5- to 30-fold relative to wild type. Because the wa1-coding sequence is identical to that of the normal mRNA, wa1 is not a null mutation. Nuclear run-on analyses revealed decreased transcription of the TGF-α gene in wa1 tissues, but the sequence of a 3.2- kb 5' flanking fragment containing the promoter was unaltered. Moreover, pulsed field gel electrophoresis analysis did not reveal alterations within 750 kb upstream or 350 kb downstream of the gene, and chromosome 6 was karyotypically normal. Hence, we speculate that the wa1 mutation may be subtle and/or reside at a greater distance from the TGF-α gene. TGF-α deficiency elicits a spectrum of variably penetrant eye anomalies in wa1 and knockout mice that are associated with open eyes at birth. We found that late-gestation wa1 and TGF-α-null embryos display a significant delay in eyelid closure, although the eyes of most embryos fuse prior to birth. In situ hybridization localized TGF-α expression to the advancing margins of the eyelid epithelium and epidermal growth factor receptor expression throughout the eyelid and corneal epithelia. These results suggest that eye problems observed in TGF-α-deficient adult mice arise from premature exposure and trauma to open eyes during or following parturition.