The Karyotype of <b><i>Salvator merianae</i></b> (Squamata, Teiidae): Analyses by Classical and Molecular Cytogenetic Techniques

Abstract

In this study, we analyzed the karyotype of Salvator merianae (Teiidae) from the Brazilian semiarid region using different cytogenetic markers. Chromosomes were examined by classical (Giemsa and AgNOR staining) and molecular (FISH with ribosomal, telomeric, and microsatellite probes) cytogenetic approaches. S. merianae showed a diploid chromosome number of 2n = 38 (10 biarmed macrochromosomes + 28 microchromosomes). No sex-linked chromosome heteromorphisms were observed. Clusters of 18S/28S rDNA were localized in the terminal region of the long arm of pair 2. In addition to the typical telomeric signals, (TTAGGG)n repeats were detected in the pericentromeric region of some macrochromosome pairs, which might indicate the occurrence of chromosomal rearrangements via chromosome fusions. Hybridization signals of the microsatellite probes (GA)n, (GAA)n, and (GAG)n were uniformly distributed across all chromosomes, while (CA)n, (CAA)n, and (CAC)n produced brighter signals in the telomeric and pericentromeric regions of specific chromosome pairs. The comparison with previous studies demonstrates that, despite the wide distribution of S. merianae, the macrostructure organization of the karyotype remained unchanged, showing stability in diploid number and chromosome morphology.

A chromosome-level genome assembly and annotation of the desert horned lizard, Phrynosoma platyrhinos, provides insight into chromosomal rearrangements among reptiles

“…3 ) [ 25 ]. The genome of S. merianae has not been assembled to chromosomes, but the karyotype of this species is known (5 macrochromosomes and 14 microchromosomes [ 39 ]), so in this study we used the 19 largest scaffolds from the S. merianae assembly (with 5 scaffolds > 200 Mb and 75 Mb > 14 scaffolds > 6 Mb). We performed synteny analyses using a “chromosome painting” technique (see Methods), which established homology between sets of 100-bp in silico “markers” from the P. platyrhinos chromosome scaffolds and regions of the genomes of the other reptile species ( Supplementary Table S5 ).…”

“…Assigning scaffolds to specific chromosomes was done using blast+2.8.0 [ 55 ] using program “blastx” (options “num_threads” = 4, “-max_target_seqs” = 10, “-evalue” = 1e-5, and “-outfmt” = 11). We used chromosome-linked gene markers in other close species ( A. carolinensis, L. reevesii ) [ 29 ] and X-linked markers in A. carolinensis [ 39 ] downloaded from NCBI ( Supplementary Table S1 ) to identify the genomic location of each gene marker. Available markers for macrochromosomes in lizards were matched to 7 of the largest scaffolds (2 scaffolds for chromosome 3), which we sorted by size and named macrochromosomes 1–6.…”

“…For posterior analyses based on the synteny results, only the assembled chromosomes of each species (based on the reference assembly) were considered. Salvator merianae was the only species in our analysis without assembled chromosomes, so we analyzed the 19 longest scaffolds (because karyotype analysis showed 2n = 38) containing the majority of confirmed markers [ 39 ].…”

Interstitial Telomeric Repeats Are Rare in Turtles

“…Cytogenetic studies have detected ITRs in numerous species across vertebrate lineages, including mammals, fishes, birds, non-avian reptiles and amphibians [3,[27][28][29][30][39][40][41][42][43][44][45][46]. In non-avian reptiles, distribution of telomeric sequences have been extensively studied in squamates, i.e., lizards and snakes, where ITRs were detected in approximately 100 species, despite the generally conserved chromosome morphology in this group [28,45,[47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. It was proposed that intrachromosomal rearrangements might have a crucial role in the formation of ITRs in squamate reptiles [28,63].…”

“…In non-avian reptiles, distribution of telomeric sequences have been extensively studied in squamates, i.e., lizards and snakes, where ITRs were detected in approximately 100 species, despite the generally conserved chromosome morphology in this group [28,45,[47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. It was proposed that intrachromosomal rearrangements might have a crucial role in the formation of ITRs in squamate reptiles [28,63]. A telomere-only pattern was instead reported in Crocodylus siamensis [65], and as far as we know, no other representative of Crocodylia has been studied.…”