TABLE 1.

Types of exRNA.

miRNA	Small, non-coding RNA (21–25 nucleotides) involved in gene regulation (He and Hannon, 2004)
mRNA	Coding RNA that evolves from DNA transcription in the process of protein biosynthesis
tRNA	Small, non-coding RNA (76–90 nucleotides) that translates mRNA sequences in proteins
rRNA	Non-coding, structural component of ribosomes
snRNA	Small, non-coding RNA (about 150 nucleotides) constitutes a part of spliceosomes (Wang et al., 2017)
lncRNA	Long non-coding RNA, >200 nucleotides
circRNA	Small, non-coding RNA contributes to gene regulation by suppressing miRNA function (Wang et al., 2017)
snoRNA	Small, non-coding RNA (60–300 nucleotides) (Wang et al., 2017) modifies tRNA and rRNA chemically (Wang et al., 2017)
piRNA	Small, non-coding RNA (24–32 nucleotides) mainly involved in gene regulation of germ line cells (Wang et al., 2017)
Y RNA	Small non-coding RNA; components of the Ro60 ribonucleoprotein particle, factor for initiation of chromosomal DNA replication (Kowalski and Krude, 2015)