The lowest diploid number in Testudines: Banding patterns, telomeric and 45S rDNA FISH in Peltocephalus dumerilianus, 2n = 26 and FN = 52 (Pleurodira, Podocnemididae)

Ventura, Karen; Moreira, Camila Nascimento; Moretti, Renata; Yonenaga‐Yassuda, Yatiyo; Rodrigues, Miguel Tréfaut

doi:10.1590/s1415-47572014000100011

Cited by 9 publications

(15 citation statements)

References 12 publications

(16 reference statements)

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“…Our finding that the NOR is located on the first chromosome pair of both PEX and PUN, associated with a secondary constriction, is consistent with previous observations in P. expansa and P. sextuberculata [ 13 , 42 ]. This suggests that the NORs are highly conserved in family Podocnemidae.…”

Section: Discussionsupporting

confidence: 93%

“…6 ). In contrast, Ventura et al [ 42 ] reported that the secondary constriction region of Peltocephalus dumerilianus presented a large block of heterochromatin. The telomeric probes hybridized with atypical regions, such as centromeres, perhaps reflecting the random amplification of telomere-like sequences or telomere remnants that remained following centric fusions that occurred during evolution [ 10 , 14 , 43 ].…”

Section: Discussionmentioning

confidence: 95%

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New insights of karyoevolution in the Amazonian turtles Podocnemis expansa and Podocnemis unifilis (Testudines, Podocnemidae)

et al. 2016

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BackgroundCytogenetic studies were conducted in the Brazilian Amazon turtles, Podocnemis expansa Schweigger, 1912 (PEX) and Podocnemis unifilis Troschel, 1848 (PUN) to understand their karyoevolution. Their chromosomal complements were compared using banding techniques (C, G-, Ag-NOR and Chromomycin A3) and fluorescence in situ hybridization (FISH), and efforts were made to establish evolutionary chromosomal relationships within the Podocnemidae family.ResultsOur results revealed that both species have a chromosome complement of 2n = 28. For PEX and PUN, the fundamental numbers (FNs) were 54 and 52, respectively and the karyotypic formulas (KFs) were 24 m/sm + 2st + 2a and 22 m/sm + 2st + 4a, respectively. G-banding evidenced homologies between the two species and allowed identify a heteromorphic pair (chromosome pair 10) in PUN. In PEX, constitutive heterochromatin (CH) was found in the centromeric regions of pairs 1, 2, 4, 6 and 11 and on 9p. In PUN, CH was observed in the centromeric regions of all chromosomes, and in small proximal bands on 1p, 2p, 3q, 4q, 5q, 9q, 10q and 11q. Moreover, CH amplification was seen in one of the homologs of pair 10 (the heteromorphic pair). The CMA3 staining results were consistent with the CH findings. Ag-NOR staining showed that nucleolar organizing regions (NORs) were localized in the pericentromeric region of pair 1 in both species, and this result was confirmed by the 18S rDNA FISH probe. FISH with telomeric probes identified telomeric sequences in the distal regions of all chromosomes. In addition, interstitial telomeric sequences (ITSs) were present in seven chromosome pairs of PUN, perhaps reflecting the amplification of telomere-like sequences. FISH with a probe against the transposable element (TE), Rex 6, revealed that it is dispersed in euchromatic regions of the first chromosome pairs of both species. This is the first report describing the FISH-based analysis of PEX and PUN for the 18S rDNA, Rex 6 and human telomeric sequences.ConclusionsOur results contribute to clarifying the chromosomal homologies and rearrangement mechanisms that occurred during the evolution of these species, and may help researchers uncover new markers that will improve our understanding of the taxonomy and systematic classification of Podocnemidae.Trial registrationISRCTN ISRCTN73824458. Registered 28 September 2014. Retrospectively registered.

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Section: Discussionsupporting

confidence: 93%

Section: Discussionmentioning

confidence: 95%

New insights of karyoevolution in the Amazonian turtles Podocnemis expansa and Podocnemis unifilis (Testudines, Podocnemidae)

et al. 2016

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“…The diploid number in turtles ranges from 2n = 26 in Peltocephalus dumerilianus [Killebrew, 1975a;Ventura et al, 2014] to 2n = 68 in Carettochelys insculpta [Bickham et al, 1983] with an average of 2n = 52 given our current knowledge of turtle chromosomes [Olmo and Signorino, 2005] ( fig. 1 ).…”

Section: Evolution Of Turtle Karyotypesmentioning

confidence: 99%

Cytogenetic Insights into the Evolution of Chromosomes and Sex Determination Reveal Striking Homology of Turtle Sex Chromosomes to Amphibian Autosomes

Montiel

Badenhorst²,

Lee³

et al. 2016

Cytogenet Genome Res

136

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Turtle karyotypes are highly conserved compared to other vertebrates; yet, variation in diploid number (2n = 26-68) reflects profound genomic reorganization, which correlates with evolutionary turnovers in sex determination. We evaluate the published literature and newly collected comparative cytogenetic data (G- and C-banding, 18S-NOR, and telomere-FISH mapping) from 13 species spanning 2n = 28-68 to revisit turtle genome evolution and sex determination. Interstitial telomeric sites were detected in multiple lineages that underwent diploid number and sex determination turnovers, suggesting chromosomal rearrangements. C-banding revealed potential interspecific variation in centromere composition and interstitial heterochromatin at secondary constrictions. 18S-NORs were detected in secondary constrictions in a single chromosomal pair per species, refuting previous reports of multiple NORs in turtles. 18S-NORs are linked to ZW chromosomes in Apalone and Pelodiscus and to X (not Y) in Staurotypus. Notably, comparative genomics across amniotes revealed that the sex chromosomes of several turtles, as well as mammals and some lizards, are homologous to components of Xenopus tropicalis XTR1 (carrying Dmrt1). Other turtle sex chromosomes are homologous to XTR4 (carrying Wt1). Interestingly, all known turtle sex chromosomes, except in Trionychidae, evolved via inversions around Dmrt1 or Wt1. Thus, XTR1 appears to represent an amniote proto-sex chromosome (perhaps linked ancestrally to XTR4) that gave rise to turtle and other amniote sex chromosomes.

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“…The members of order Testudines may be subdivided in two suborders (Cryptodira and Pleurodira) and comprise one of the oldest lineages of existing vertebrates [ 1 ]. Studies have revealed a high degree of karyotypic variation in this order; the diploid numbers (2n) range from 26 in Peltocephalus dumerilianus (Pleurodira, Podocnemididae) [ 2 , 3 ] to 68 in Carettochelys insculpta (Cryptodira, Carettochelyidae) [ 4 , 5 ], with 2n = 52 reported as the most frequent diploid number [ 5 ]. The karyotypic diversity of the Testudines is attributed mainly to the presence/absence of microchromosomes.…”

Section: Introductionmentioning

confidence: 99%

Physical mapping of repetitive DNA suggests 2n reduction in Amazon turtles Podocnemis (Testudines: Podocnemididae)

Cavalcante¹,

Bastos²,

Nagamachi³

et al. 2018

PLoS ONE

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Cytogenetic studies show that there is great karyotypic diversity in order Testudines (2n = 26–68), and that this may be mainly attributed to the presence/absence of microchromosomes. Members of the Podocnemididae family have the smallest diploid numbers of this order (2n = 26–28), which may be a derived condition of the group. Diverse studies suggest that repetitive-DNA-rich sites generally act as hotspots for double-strand breaks and chromosomal reorganization. In this context, we used fluorescent in situ hybridization (FISH) to map telomeric sequences (TTAGGG)n, 45S rDNA, and the genes encoding histones H1 and H3 in two species of genus Podocnemis. We also observed conservation of the 45S rDNA and H1 histone sequences (probable case of conserved synteny), but multiple conserved and non-conserved clusters of H3 genes, which colocalized with the interstitial telomeric sequences in the Podocnemis genome. Our results suggest that fusions have occurred between macro and microchromosomes or between microchromosomes, leading to the observed reduction in diploid number in the family Podocnemididae.

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The lowest diploid number in Testudines: Banding patterns, telomeric and 45S rDNA FISH in Peltocephalus dumerilianus, 2n = 26 and FN = 52 (Pleurodira, Podocnemididae)

Cited by 9 publications

References 12 publications

New insights of karyoevolution in the Amazonian turtles Podocnemis expansa and Podocnemis unifilis (Testudines, Podocnemidae)

New insights of karyoevolution in the Amazonian turtles Podocnemis expansa and Podocnemis unifilis (Testudines, Podocnemidae)

Cytogenetic Insights into the Evolution of Chromosomes and Sex Determination Reveal Striking Homology of Turtle Sex Chromosomes to Amphibian Autosomes

Physical mapping of repetitive DNA suggests 2n reduction in Amazon turtles Podocnemis (Testudines: Podocnemididae)

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