Figure 4. Altered expression levels of RNA processing enzymes Drosha and Dicer, and Alu-like RNAs in OIR are consistent with relatively down-regulated mature miRNA levels compared with pre-miRNAs.

(a) Heat map illustration of miRNA array data shows those miRNAs with significantly changed levels (P < 0.05) in OIR mouse retinas compared with age-matched normoxic retinas. Red color indicates up-regulated expression levels in OIR; green color indicates down-regulated expressing levels. (b) Schematic diagram of the miRNA biogenesis. MiRNA genes are usually transcribed by RNA polymerase II to the primary miRNAs (pri-miRNAs), which are processed by Drosha, yielding precursor miRNAs (pre-miRNAs) in the nucleus. After being exported to the cytoplasm, the pre-miRNAs are cleaved by Dicer to generate sense (mature) miRNA:anti-sense miRNA* duplexes. Following unwinding of the miRNA duplexes, the single-strain mature miRNAs are assembled into the RNA-induced silencing complex (RISC) for binding to their target mRNAs to mediate transcription repression or degradation. (c) Heat map shows relatively up-regulated pre-miRNA levels in P17 OIR mouse retinas compared with normoxic control retinas, along with corresponding antisense (*) and sense (mature) miRNA levels. Red indicates up-regulated expression level; green indicates down-regulated expression level. (d) Gene expression levels of Drosha and Dicer1 in normoxic (Normal) and OIR mouse retinas were measured by RT-qPCR. (e) Expression levels of transcription repressive B1/B2 in normal and OIR retinas. Results were normalized to housekeeping gene 18S and to expression levels in age-matched normoxic controls. Data were presented as mean ± SEM, n = 6 per experimental group.