The Tudor-domain protein TDRD7, mutated in congenital cataract, controls the heat shock protein HSPB1 (HSP27) and lens fiber cell morphology

Abstract

<jats:title>Abstract</jats:title> <jats:p>Mutations of the RNA granule component TDRD7 (OMIM: 611258) cause pediatric cataract. We applied an integrated approach to uncover the molecular pathology of cataract in Tdrd7−/− mice. Early postnatal Tdrd7−/− animals precipitously develop cataract suggesting a global-level breakdown/misregulation of key cellular processes. High-throughput RNA sequencing integrated with iSyTE-bioinformatics analysis identified the molecular chaperone and cytoskeletal modulator, HSPB1, among high-priority downregulated candidates in Tdrd7−/− lens. A protein fluorescence two-dimensional difference in-gel electrophoresis (2D-DIGE)-coupled mass spectrometry screen also identified HSPB1 downregulation, offering independent support for its importance to Tdrd7−/− cataractogenesis. Lens fiber cells normally undergo nuclear degradation for transparency, posing a challenge: how is their cell morphology, also critical for transparency, controlled post-nuclear degradation? HSPB1 functions in cytoskeletal maintenance, and its reduction in Tdrd7−/− lens precedes cataract, suggesting cytoskeletal defects may contribute to Tdrd7−/− cataract. In agreement, scanning electron microscopy (SEM) revealed abnormal fiber cell morphology in Tdrd7−/− lenses. Further, abnormal phalloidin and wheat germ agglutinin (WGA) staining of Tdrd7−/− fiber cells, particularly those exhibiting nuclear degradation, reveals distinct regulatory mechanisms control F-actin cytoskeletal and/or membrane maintenance in post-organelle degradation maturation stage fiber cells. Indeed, RNA immunoprecipitation identified Hspb1 mRNA in wild-type lens lysate TDRD7-pulldowns, and single-molecule RNA imaging showed co-localization of TDRD7 protein with cytoplasmic Hspb1 mRNA in differentiating fiber cells, suggesting that TDRD7–ribonucleoprotein complexes may be involved in optimal buildup of key factors. Finally, Hspb1 knockdown in Xenopus causes eye/lens defects. Together, these data uncover TDRD7’s novel upstream role in elevation of stress-responsive chaperones for cytoskeletal maintenance in post-nuclear degradation lens fiber cells, perturbation of which causes early-onset cataracts.</jats:p>

LOTUS-domain proteins - developmental effectors from a molecular perspective

“…In addition to brain and testes, TDRD7 is highly enriched in the developing ocular lens of vertebrates and its deficiency in chicken, mice and human causes eye defects such as cataract and glaucoma (Chen et al 2017;Lachke et al 2011;Tan et al 2019;Tanaka et al 2011b). In the lens, TDRD7 was suggested to bind and post-transcriptionally regulate mRNAs that encode factors critical for lens development (Barnum et al 2020;Lachke et al 2011).…”

Identification of Differential Gene Expression Pattern in Lens Epithelial Cells Derived from Cataractous and Noncataractous Lenses of Shumiya Cataract Rat

“…Fold changes (<0.5-fold) were observed in 20 top-ranked genes ( Table 1 ) in the microarray analysis including Dnase2B , HspB1, γCry , Mip , beaded filament structural protein 1 ( Bfsp1 ), and Lgsn that have been reported to be associated with cataract and lens development [ 22 – 27 ]. Additionally, Hsf4 , Tdrd7 , gap junction protein epsilon 1 ( Gje1 ), beaded filament structural protein 2 ( Bfsp2 ), and lens intrinsic membrane protein 2 ( Lim2 ) which are also significantly reduced in the SCR lens (<0.5-fold) were linked to human or animal cataracts (Supplement 1) [ 27 – 33 ]. Furthermore, the expressions of six genes were upregulated (2.1- to 2.5-fold) in rat LECs from Cat+ compared to those from Cat-.…”

“…Furthermore, the mutations of Tdrd7 also cause human congenital and age-related cataracts [ 30 , 31 ]. Hsf4 - knockout mice ( Hsf4 −/− ) and Tdrd7 -homozygous KO mice ( Tdrd7 −/− ) also cause cataracts [ 32 , 33 ]. Among 111 genes whose expression was decreased by LECs of Cat+ SCR, genes whose expression was also changed by the lens of Hsf4 -conditional knockout mice ( Hsf4 -CKO) or Tdrd7 -homozygous KO mice ( Tdrd7 −/− ) were analyzed using the iSyTE database (PMID: 29036527 and PMID: 32420594, respectively).…”

RNA-Binding Protein Rbm24 as a Multifaceted Post-Transcriptional Regulator of Embryonic Lineage Differentiation and Cellular Homeostasis

“…The importance of post-transcriptional regulation after lens fiber cell denucleation has been also demonstrated for other aspects of lens morphogenesis. Analysis of TDRD7 function in mice indicates that it is required for maintaining cytoskeletal organization and lens fiber cell morphology by regulating the expression of heat shock protein HSPB1 [ 82 ]. Moreover, members of the PABPC family are ancient paralogs of Rbm24, and they are coexpressed in different tissues.…”