Parrott Andrew M, Mathews Michael B
Department of Biochemistry and Molecular Biology; New Jersey Medical School; University of Medicine and Dentistry of New Jersey; Newark, NJ USA.
Mob Genet Elements. 2011 Nov 1;1(4):291-295. doi: 10.4161/mge.18478.
The small NF90 associated RNA (snaR) family of small noncoding RNAs (ncRNA) appears to have evolved from retrotransposon ancestors at or soon after pivotal stages in primate evolution. snaRs are thought to be derived from a FLAM C-like (free left Alu monomer) element through multiple short insertion/deletion (indel) and nucleotide (nt) substitution events. Tracing snaR's complex evolutionary history through primate genomes led to the recent discovery of two novel retrotransposons: the Alu/snaR related (ASR) and catarrhine ancestor of snaR (CAS) elements. ASR elements are present in the genomes of Simiiformes, CAS elements are present in Old World Monkeys and apes, and snaRs are restricted to the African Great Apes (Homininae, including human, gorilla, chimpanzee and bonobo). Unlike their ancestors, snaRs have disseminated by multiple rounds of segmental duplication of a larger encompassing element. This process has produced large tandem gene arrays in humans and possibly precipitated the accelerated evolution of snaR. Furthermore, snaR segmental duplication created a new form of chorionic gonadotropin β subunit (CGβ) gene, recently classified as Type II CGβ, which has altered mRNA tissue expression and can generate a novel short peptide.
小非编码RNA（ncRNA）的小NF90相关RNA（snaR）家族似乎是在灵长类动物进化的关键阶段或之后不久从逆转录转座子祖先进化而来的。snaR被认为是通过多个短插入/缺失（indel）和核苷酸（nt）取代事件从类似FLAM C（游离左Alu单体）的元件衍生而来。通过灵长类动物基因组追踪snaR复杂的进化历史，最近发现了两种新型逆转录转座子：Alu/snaR相关（ASR）元件和snaR的狭鼻猴祖先（CAS）元件。ASR元件存在于类人猿基因组中，CAS元件存在于旧世界猴和猿类中，而snaR仅限于非洲大猿（人亚科，包括人类、大猩猩、黑猩猩和倭黑猩猩）。与它们的祖先不同，snaR通过更大的包含元件的多轮片段重复进行传播。这一过程在人类中产生了大型串联基因阵列，并可能促使snaR加速进化。此外，snaR片段重复产生了一种新形式的绒毛膜促性腺激素β亚基（CGβ）基因，最近被归类为II型CGβ，它改变了mRNA的组织表达，并能产生一种新的短肽。
