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H. Huang, K. J. Wahlin, M. McNally, R. Adler; Regulation of Muscleblind Gene Expression During Chick Retinal Development. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4475.
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© ARVO (1962-2015); The Authors (2016-present)
Muscleblind-like (MBNL) zinc finger proteins regulate development of muscle and photoreceptors in Drosophila, are conserved in vertebrates, and are associated with Myotonic Distrophy. Their expression patterns and developmental roles in the retina in general, and photoreceptors in particular, have not been investigated. As an initial approach to these questions, we have examined the expression of the MBNL -1, -2 and -3 genes in the developing chick embryo retina.
Retinas from different chick embryo stages [embryonic day (ED) 6-18] were dissected for RNA isolation or fixed and crysectioned for in situ hybridization (ISH) or immunocytochemistry (ICC). Transcript variants and changes in expression levels were studied by Northern blots and quantitative (Q) PCR. Cell suspensions from dissociated ED20 retinas were fixed for ICC analysis.
All MBNL genes increased expression levels during development and, as in other species, showed two or more transcript variants. By ISH, all MBNL mRNAs had widespread patterns of expression at earlier embryonic stages (ED 6-8), becoming subsequently enriched in (but not restricted to) the scleral side of the inner nuclear layer. Temporal and spatial patterns of MNBL-1 and-2 immunoreactivity were much more restricted than those seen by ISH. Thus, while MBNL 1- and -2 mRNAs were present throughout the retina at ED5-7, corresponding ICC retinal signals were strong at the periphery but very weak or even undetectable more centrally. In the fundal region MBNL-1 and MBNL-2 immunoreactivities only became detectable around ED 11-13, and were restricted to only some of the cells (+) for the cognate mRNAs, particularly ganglion cells and photoreceptors. MBNL-1 and -2 ICC signals were first seen in photoreceptor inner segments, where they remained for MBNL2 at later stages; MBNL1, however, became subsequently localized to photoreceptor synaptic terminals.
These expression patterns are consistent with the possibility that MNBLs may regulate photoreceptor development in a vertebrate retina, much as they do in Drosophila, and suggest that the expression of MBNL-1 and -2 is likely to be regulated post-transcriptionally.
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