Heterogeneous distribution of retinal degeneration protein 3 in human fetal normal tissues

Abstract

Natarajan Aravindan, Dinesh Babu Somasundaram, Sheeja Aravindan, Zhongxin Yu,Karthikeyan Subramanian, Terence S. Herman

Background: Our studies identified the loss of Retinal degeneration Protein 3 (RD3) in the predominant infant tumor, neuroblastoma, indicated its novel regulatory function in neuroblastoma pathogenesis, and showed its localization in tissues beyond the retina. To explore the possible physiological role of RD3 in regulating the genesis of neuroblastoma, its distribution in human fetal normal tissues was examined. Methods: Constitutive mRNA levels [quantitative polymerase chain reaction (QPCR), RNAscope], protein expression (immunohistochemistry), and sub-cellular localization of RD3 were investigated in an array (20 sites) of human (n = 5) fetal normal tissues. In silico RNA sequencing data from seven independent studies (total n = 407) of human fetal tissues (101 sites) were utilized to validate the differential expression of RD3 in developing tissues. Results: RNAscope and QPCR analysis indicated a steady-state RD3 transcription across the fetal tissues with measurable inter-tissue differences (e.g., high in GI tissues versus and low in the adrenal gland). RNA-seq data on varying stages of development clearly indicated stage-dependent dynamic fluctuations in RD3 transcription as the development progress. Notably, RD3 transcription is stably expressed in choroid plexus and is relatively absent in the spinal cord through the developmental stages. Immunohistochemistry analysis recognized the presence of RD3 protein in the array of fetal normal tissues, the tissue- and cell-specific distinctions in protein expression, and the variances in sub-cellular localization with each tissue. Conclusions: The results presented in this study revealed the tissue-specific transcription, expression, and localization of RD3 in fetal tissues. Recognizing the heterogeneous expression of RD3 between and within the fetal tissues signifies its possible functions beyond photoreceptor cell survival and could shed light on its functional relevance in neuroblastoma genesis and/or evolution.