Developmental regulation of muscleblind‐like (MBNL) gene expression in the chicken embryo retina

Abstract

Muscleblind-like (MBNL) is a CCCH zinc finger-containing RNA-binding protein required for the development of both muscle and photoreceptors in Drosophila; it is conserved evolutionarily, and it is associated in humans with the muscular disease myotonic dystrophy. Its role in the development of vertebrate retinal cells, however, remains unknown. As an initial approach to its investigation, we have cloned three chick muscleblind genes, characterized their isoforms, and examined their expression patterns in the chick embryo retina. The relative levels of expression of the MBNL genes increased during embryonic development. In situ hybridization (ISH) showed that the three MBNL mRNAs had widespread patterns of expression at all the developmental stages examined. Of interest, the temporal and spatial patterns of protein expression, detected by immunocytochemistry with antibodies against MBNL1 and MBNL2, were much more restricted than those seen by ISH. At early stages (ED5-7), for example, MBNL1 and MBNL2 mRNAs were present throughout the retina, but immunoreactivity for the corresponding proteins was largely restricted to the periphery of the optic cup (presumptive iris/ciliary epithelium/ciliary margin zone). MBNL1 and MBNL2 immunoreactivity became detectable at the fundus at later stages, but was limited to a very small subset of the cells that had ISH signals for the cognate mRNAs (particularly ganglion cells and photoreceptors). Within photoreceptors, MBNL1 and MBNL2 immunoreactivity first appeared in their inner segments; MBNL2 remained there, but MBNL1 became subsequently localized to their synaptic terminals. These expression patterns are consistent with the possibility that MBNLs may regulate photoreceptor development in the chick retina, much as MBL does in Drosophila, and suggest that the expression of MBNL1 and MBNL2 may be regulated posttranscriptionally. Developmental Dynamics 237: 286 -296, 2008.

Deterministic splicing ofDscam2is regulated by Muscleblind

“…Consistent with what has been reported in nematodes (Norris et al, 2017), zebrafish (Machuca-Tzili et al, 2011) and chickens (Huang et al, 2008), we demonstrated cell-typespecific expression of mbl. Mbl was present in all cells tested that express Dscam2.10B and absent from Dscam2.10A cells.…”

Transcriptionally correlated subcellular dynamics of MBNL1 during lens development and their implication for the molecular pathology of myotonic dystrophy type 1

“…Minor disruptions can have profound consequences in the lens since it has little opportunity to repair or recover from defects in its highly ordered programme of differentiation. The Drosophila homolog of MBNL1, muscleblind, was originally isolated as a gene required for photoreceptor differentiation [45], while MBNL proteins have been demonstrated to be developmentally regulated in the chick retina [46]. Recent RNA sequencing data has implicated MBNL proteins as key negative regulators of transcriptional pathways involved in the maintenance of pluripotency in embryonic stem cells, with over--expression of MBNL proteins promoting alternative splicing patterns associated with differentiated cells [11].…”

Muscleblind-Like Proteins

“…An unexpected function for MBNL2 in cytoplasmic mRNA transport has been reported, 39 but it is not yet known whether MBNL1 can also perform this function. In embryonic chick retina development, MBNL1 and MBNL2 become distributed in different regions of the photoreceptor, 52 but it is not known whether they perform similar or different functions there. Nuclear foci in DM1 myoblast cultures were labeled by in situ hybridization, and creatine kinase (CK) was labeled with CK-JAC mAb ͓46͔.…”