Chromosome spreading of the (TTAGGG)n repeats in the Pipa carvalhoi Miranda-Ribeiro, 1937 (Pipidae, Anura) karyotype

Abstract

Pipidae is a clade of Anura that diverged relatively early from other frogs in the phylogeny of the group. Pipids have a unique combination of morphological features, some of which appear to represent a mix of adaptations to aquatic life and plesiomorphic characters of Anura. The present study describes the karyotype of Pipa carvalhoi Miranda-Ribeiro, 1937, including morphology, heterochromatin distribution, and location of the NOR site. The diploid number of P. carvalhoi is 2n=20, including three metacentric pairs (1, 4, 8), two submetacentric (2 and 7), three subtelocentric (3, 5, 6), and two telocentric pairs (9 and 10). C-banding detected centromeric blocks of heterochromatin in all chromosome pairs and the NOR detected in chromosome pair 9, as confirmed by FISH using the rDNA 28S probe. The telomeric probes indicated the presence of interstitial telomeric sequences (ITSs), primarily in the centromeric region of the chromosomes, frequently associated with heterochromatin, suggesting that these repeats are a significant component of this region. The findings of the present study provide important insights for the understanding of the mechanisms of chromosomal evolution in the genus Pipa, and the diversification of the Pipidae as a whole.

Evolutionary Dynamics of the Repetitive DNA in the Karyotypes of Pipa carvalhoi and Xenopus tropicalis (Anura, Pipidae)

“…Pericentromeric inversions are the most parsimonious hypothesis to account for the chromosomal changes between the inferred primitive pipid karyotype (which is conserved in X. tropicalis) and P. carvalhoi (Mezzasalma et al, 2015). The presence of the ITSs reported by Zattera et al (2019) and our new chromosome markers [(GA) 15 , (GACA) 4 , (CAG) 10 , and (GA) 15 motifs] reinforce these hypotheses.…”

“…The presumable primitive karyotype of the Pipidae, for example (which is conserved in X. tropicalis), indicates the occurrence of five pericentromeric inversions (in pairs 3, 6, 8, 9, and 10) in the P. carvalhoi karyotype (Mezzasalma et al, 2015) and three inversions (in pairs 6, 8 and 10) in P. merli (Mezzasalma et al, 2015). Recently, Zattera et al (2019) validated some of these pericentromeric inversions in P. carvalhoi by FISH assays, as confirmed by the presence of the interstitial telomeric sequences (ITS) in the homologs of pairs 6, 8, and 9.…”

“…The 2 n = 20 karyotype is a putative plesiomorphic condition in the family Pipidae ( Morescalchi, 1981 ; Mezzasalma et al, 2015 ; Zattera et al, 2019 ). This condition can be observed in the karyotypes of Pipa carvalhoi , Pseudhymenochirus merli , Hymenochirus boettgeri , and in Xenopus tropicalis ( Tymowska and Fischberg, 1973 ; Mezzasalma et al, 2015 ; Zattera et al, 2019 ). In the genus Xenopus , in particular, two well-supported clades have been recognized ( Evans et al, 2019 ).…”

“…One clade, known as the X. tropicalis group, includes the species with 2 n = 20 chromosomes and the polyploid species derived from this basic type [2 n = 4 x = 40: X. calcaratus ; X. epitropicalis ; X. mellotropicalis ] ( Evans et al, 2015 ). The second clade, known as the Xenopus laevis group, encompasses 25 species, with diploid numbers ranging from 4 n = 36 to 12 n = 108, resulting from a series of independent allopolyploidization events beginning with an ancestral karyotype of 2 n = 18 chromosomes (see the list to Zattera et al, 2019 ). In this case, the primitive 2 n = 18 karyotype appears to have been derived from the fusion of chromosomes 9 + 10 in the ancestral 2 n = 20 karyotype ( Mezzasalma et al, 2015 ; Session et al, 2016 ).…”

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].…”