Determining the roles of MAB21L2 during normal eye development and how mutations result in eye developmental defects

Abstract

Purpose : Mutations in MAB21L2 result in colobomas and associated eye defects. The molecular and cellular underpinnings of these defects are unknown, and the normal cellular function of MAB21L2 is likewise enigmatic given that it possesses no recognizable protein motifs. Zebrafish mab21l2 mutants possess ocular defects resembling those in humans with MAB21L2 mutations and thus, provide an excellent model through which the role of mab21l2 during normal eye development can be identified.

Methods : Eyes from mab21l2 mutants and wild-type siblings were examined over time through histological methods to determine the onset and progression of ocular defects. Chromatin fractionation was used to determine cellular localization of the mab21l2 protein. Yeast-2-hybrid analysis was used to determine possible binding partners for mab21l2. Finally, RNA carrying mutations in MAB21L2 detected in patients was injected into zebrafish to determine how the mutations affect normal MAB21L2 function.

Results : Histological analysis shows some mab21l2 mutants appear to fail to initiate lens morphogenesis, while others begin morphogenesis with a slight delay and possess an overall slower growth rate, leading to dramatic differences in lens size at later ages. In addition, preliminary results show that mab21l2 is localized to the nucleus and is in the chromatin fraction, suggesting that it could be involved in transcriptional regulation. Yeast-2-hybrid results identified putative interactions with proteins that function in nuclear transport, cytoskeletal remodeling, and transcriptional regulation, among others, suggesting a variety of potential cellular functions. Preliminary expression of mutant MAB21L2 constructs suggest that MAB21L2^R51C and MAB21L2^R51H may act as dominant negative or gain of function alleles, while MAB21L2^E49K and MAB21L2^R247Q are non-functional.

Conclusions : Our data suggest that mab21l2 may have a transcriptional regulatory function, perhaps affecting cell proliferation or survival during early eye development. Expression of MAB21L2^R51C and MAB21L2^R51H in zebrafish suggests that this amino acid is critical for normal MAB21L2 function, and, when mutated, displays dominant negative or gain of function activity. Potential binding partners for mab21l2 have been identified and further characterization should shed light on the function of this enigmatic protein during normal eye development.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.