SINE-derived satellites in scaled reptiles.

BACKGROUND: The genomes of many eukaryotes contain DNA repeats in the form of both tandem and interspersed elements with distinct structure, evolutionary histories, and mechanisms of emergence and amplification. Although there is considerable knowledge regarding their diversity, there is little evidence directly linking these two types. RESULTS: Different tandem repeats derived from portions of short interspersed elements (SINEs) belonging to different families were identified in 56 genomes of squamate reptiles. All loci of SINE-derived satellites (sSats) were thoroughly analyzed. Snake sSats exhibited high similarity in both structure and copy number, while other taxa may have highly diverse (geckos), rare (Darevskia lizards), or missing sSats (agamid lizards). Similar to most satellites associated with heterochromatin, sSats are likely linked to subtelomeric chromosomal regions. CONCLUSIONS: Discovered tandem repeats derived from SINEs exhibit satellite-like properties, although they have not amplified to the same degree as typical satellites. The autonomous emergence of distinct sSats from diverse SINE families in numerous squamate species suggests a nonrandom process of satellite genesis originating from repetitive SINEs.

Tail Wags Dog's SINE: Retropositional Mechanisms of Can SINE Depend on Its A-Tail Structure.

SINEs, non-autonomous short retrotransposons, are widespread in mammalian genomes. Their transcripts are generated by RNA polymerase III (pol III). Transcripts of certain SINEs can be polyadenylated, which requires polyadenylation and pol III termination signals in their sequences. Our sequence analysis divided Can SINEs in canids into four subfamilies, older a1 and a2 and younger b1 and b2. Can_b2 and to a lesser extent Can_b1 remained retrotranspositionally active, while the amplification of Can_a1 and Can_a2 ceased long ago. An extraordinarily high Can amplification was revealed in different dog breeds. Functional polyadenylation signals were analyzed in Can subfamilies, particularly in fractions of recently amplified, i.e., active copies. The transcription of various Can constructs transfected into HeLa cells proposed AATAAA and (TC)n as functional polyadenylation signals. Our analysis indicates that older Can subfamilies (a1, a2, and b1) with an active transcription terminator were amplified by the T+ mechanism (with polyadenylation of pol III transcripts). In the currently active Can_b2 subfamily, the amplification mechanisms with (T+) and without the polyadenylation of pol III transcripts (T-) irregularly alternate. The active transcription terminator tends to shorten, which renders it nonfunctional and favors a switch to the T- retrotransposition. The activity of a truncated terminator is occasionally restored by its elongation, which rehabilitates the T+ retrotransposition for a particular SINE copy.

Analysis of SINE Families B2, Dip, and Ves with Special Reference to Polyadenylation Signals and Transcription Terminators.

Short Interspersed Elements (SINEs) are eukaryotic non-autonomous retrotransposons transcribed by RNA polymerase III (pol III). The 3'-terminus of many mammalian SINEs has a polyadenylation signal (AATAAA), pol III transcription terminator, and A-rich tail. The RNAs of such SINEs can be polyadenylated, which is unique for pol III transcripts. Here, B2 (mice and related rodents), Dip (jerboas), and Ves (vespertilionid bats) SINE families were thoroughly studied. They were divided into subfamilies reliably distinguished by relatively long indels. The age of SINE subfamilies can be estimated, which allows us to reconstruct their evolution. The youngest and most active variants of SINE subfamilies were given special attention. The shortest pol III transcription terminators are TCTTT (B2), TATTT (Ves and Dip), and the rarer TTTT. The last nucleotide of the terminator is often not transcribed; accordingly, the truncated terminator of its descendant becomes nonfunctional. The incidence of complete transcription of the TCTTT terminator is twice higher compared to TTTT and thus functional terminators are more likely preserved in daughter SINE copies. Young copies have long poly(A) tails; however, they gradually shorten in host generations. Unexpectedly, the tail shortening below A10 increases the incidence of terminator elongation by Ts thus restoring its efficiency. This process can be critical for the maintenance of SINE activity in the genome.

New Ther1-derived SINE Squam3 in scaled reptiles.

BACKGROUND: SINEs comprise a significant part of animal genomes and are used to study the evolution of diverse taxa. Despite significant advances in SINE studies in vertebrates and higher eukaryotes in general, their own evolution is poorly understood. RESULTS: We have discovered and described in detail a new Squam3 SINE specific for scaled reptiles (Squamata). The subfamilies of this SINE demonstrate different distribution in the genomes of squamates, which together with the data on similar SINEs in the tuatara allowed us to propose a scenario of their evolution in the context of reptilian evolution. CONCLUSIONS: Ancestral SINEs preserved in small numbers in most genomes can give rise to taxa-specific SINE families. Analysis of this aspect of SINEs can shed light on the history and mechanisms of SINE variation in reptilian genomes.

Short interspersed elements (SINEs) of squamate reptiles (Squam1 and Squam2): structure and phylogenetic significance.

Short interspersed elements (SINEs) are important nuclear molecular markers of the evolution of many eukaryotes. However, the SINEs of squamate reptile genomes have been little studied. We first identified two families of SINEs, termed Squam1 and Squam2, in the DNA of meadow lizard Darevskia praticola (Lacertidae) by performing DNA hybridization and PCR. Later, the same families of retrotransposons were found using the same methods in members of another 25 lizard families (from Iguania, Scincomorpha, Gekkota, Varanoidea, and Diploglossa infraorders) and two snake families, but their abundances in these taxa varied greatly. Both SINEs were Squamata-specific and were absent from mammals, birds, crocodiles, turtles, amphibians, and fish. Squam1 possessed some characteristics common to tRNA-related SINEs from fish and mammals, while Squam2 belonged to the tRNA(Ala) group of SINEs and had a more unusual and divergent structure. Squam2-related sequences were found in several unannotated GenBank sequences of squamate reptiles. Squam1 abundance in the Polychrotidae, Agamidae, Leiolepididae, Chamaeleonidae, Scincidae, Lacertidae, Gekkonidae, Varanidae, Helodermatidae, and two snake families were 10(2) -10(4) times higher than those in other taxa (Corytophanidae, Iguanidae, Anguidae, Cordylidae, Gerrhosauridae, Pygopodidae, and Eublepharidae). A less dramatic degree of copy number variation was observed for Squam2 in different taxa. Several Squam1 copies from Lacertidae, Chamaeleonidae, Gekkonidae, Varanidae, and Colubridae were sequenced and found to have evident orthologous features, as well as taxa-specific autapomorphies. Squam1 from Lacertidae and Chamaeleonidae could be divided into several subgroups based on sequence differences. Possible applications of these SINEs as Squamata phylogeny markers are discussed.