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S.–L. Fong, W.–B. Fong; Activity of Gnat2 Promoter in Developing Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3134.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: When a minigene containing the human transducin α–subunit (GNAT2) promoter, an interstitial retinoid–binding protein (IRBP) enhancer and a diphtheria toxin A (DT–A) gene was introduced into a mouse embryo, a transgenic mouse (h–gnat2pro–DT–A) lacking both rod and cone photoreceptors in the ventral retina and missing most of the cone photoreceptors in the dorsal retina was generated (ARVO Annual Meeting 2003, 4516). The goal of this study was to investigate the function of cone–specific GNAT2 promoter in this mouse line between postnatal day 0 (P0) and P8. Methods: Total RNAs were prepared from transgenic retinas between P0 and P8. The expression of DT–A and GNAT2 genes during retinal morphogenesis between P0 and P8 was monitored by RT–PCR. Results: A weak human GNAT2 promoter between –151 and +126 was cone photoreceptor cell–specific and a strong positive element between +143 and +167 was noncell–specific were reported (IOVS 1997, 38:196–206). The two homologous elements were also found in corresponding locations in the mouse gene. The cone–specific promoter has 68.8% and the positive element has 76% identity between the two species if the insertion and deletion fragments were not counted. The expression of toxin gene driven by human cone–specific promoter in the h–gnat2pro–DT–A transgenic mouse was detected before postnatal day 6 (P6) by RT–PCR. After P8, the DT–A expression was completely disappeared. As controls, the total RNA samples were also used as templates for PCR without the reverse transcription step; no bands were amplified between P0 and P8. However, the endogenous GNAT2 gene was actively expressed during this period and throughout animal’s life. Conclusions: The cone cell–specific promoter by itself was active only before the retinal layers began to develop, or before P8. After P8, this promoter was no longer active, and the toxin effect did no longer exist. Additional elements, such as the noncell–specific positive element might be required to confer promoter activity. This hypothesis could explain the expression of endogenous GNAT2 gene which was detectable at all times during the period of investigation and beyond.
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