The biological role of naturalantisense transcripts in zebrafishdevelopment

Abstract

Non-coding RNAs (ncRNAs) have recently emerged as important regulators of gene expression and are now appreciated to control development, homeostasis and evolution of higher organisms. Natural antisense transcripts (NATs), a form of long ncRNA, are fully processed mRNA-like transcripts originating from the opposite strand of protein coding genes. NATs are believed to regulate the expression of the corresponding sense transcripts and may lead to transcriptional silencing. A few bidirectionally transcribed genes have been studied extensively. Ectopically expressed NATs have also been linked to diseases such as cancer, Alzheimer’s and α- thalassemia. However, many questions remain about the specific biological roles and mechanisms of actions of NATs. This study examines a specific sense/antisense system during zebrafish embryogenesis where the sense transcript, Slc34a2a, encodes a Na+-dependent phosphate transporter. The Slc34a2a sense and antisense (Slc34a2a(as)) transcripts demonstrate a reciprocal relationship were both transcripts are expressed at a near equal amount at 48 hours post fertilization. Both transcripts locate to the same tissues: the pharynx, endoderm, primordial midbrain channel and primordial hindbrain channel. No relation was found between Slc34a2a(as) and the paralog Slc34a2b. Slc34a2a(as) shares a bidirectional promoter with Rbpja but does not undergo simultaneous divergent transcription. Ectopic overexpression of Slc34a2a RNA during early embryogenesis caused failure to develop a cerebellum. Cerebellar loss lead to behavioral impairments including loss of balance and delayed reaction times. Upon investigating the molecular basis for the deleterious effect, overexpression of the protein was ruled out via injection of a frameshift containing Slc34a2a RNA. Injections of RNA fragments from the Slc34a2a locus determined that cerebellar development failure required Slc34a2a/Slc34a2a(as) RNA complementarity. The phenotype was rescued by Dicer knockdown, indicating short interfering RNA (siRNA) formation through RNAi. Mapping and extraction of synthesised and endogenous dsRNA with an anti-dsRNA monoclonal antibody was unsuccessful. Additional experiments are required to determine the exact function of Slc34a2a(as) in zebrafish embryogenesis though ii knock-out and methylation studies. Further conditions need be examined to determine the specific circumstances under which J2 antibody would be able to extract dsRNA from whole fish.