<b><i>Silurana</i></b> Chromosomal Evolution: A New Piece to the Puzzle

Abstract

The African clawed frogs of the subgenus Silurana comprise both diploid and tetraploid species. The root of the polyploidization event leading to the extant Xenopus calcaratus, X. mellotropicalis, and X. epitropicalis is not fully understood so far. In X. mellotropicalis, we previously proposed 2 evolutionary scenarios encompassing complete (scenario A) or incomplete (scenario B) translocation of a heterochromatic block from chromosome 9 to 2 in a diploid ancestor. To resolve this puzzle, we performed FISH coupled with tyramide signal amplification (FISH-TSA) using 5 X. tropicalis and X. mellotropicalis single copy gene probes (gyg2, cept1, fn1, ndufs1, and sf3b1) reflecting borders of the heterochromatic blocks in X. tropicalis chromosome 9 (XTR 9) and X. mellotropicalis chromosome 9b (XME 9b) and XME 2a. cDNA sequencing recognized both homoeologous genes in X. mellotropicalis. Comparison of gene physical mapping between X. tropicalis and X. mellotropicalis clearly confirmed complete rather than incomplete translocation t(9;2) of the heterochromatic block in the diploid predecessor and thus favored scenario A regarding the formation of an ancestral allotetraploid karyotype.

Measurement of Chromosomal Arms and FISH Reveal Complex Genome Architecture and Standardized Karyotype of Model Fish, Genus Carassius

“…In total 44 L of the hybridization mixture containing 100 ng of either 5S or 28S rDNA probe, 50% deionized formamide, 2× SSC, 10% dextran sulphate and water was placed on a slide and covered with a 24 × 50 mm coverslip. Both probe and chromosomal DNA were denatured in a PCR machine with special block for slides at 70 °C for 5 min [ 9 ]. Hybridization, post-hybridization washing, blocking reaction and visualization of 5S and 28S rDNA signals were carried out as described in Knytl et al [ 39 ].…”

“…Knowledge of the karyotype is necessary in (cyto)genetics, or related fields, in order to study chromosomal rearrangements and abnormalities [5,6], the identification of sex chromosomes [7,8], and/or chromosome-specific genes [9]. Although chromosomal changes, (i.e., chromosomal losses, duplications, rearrangements), are strictly linked to a certain locus, without the knowledge of detailed karyotype, it is not possible to precisely identify chromosomal aberration, mutation or syndrome [10,11].…”

“…Heteromorphic sex chromosomes (morphologically distinct in male or female individuals) can be distinguished by classic cytogenetic procedures based on Giemsa-staining karyogram of both sexes and/or by chromosome painting and fluorescent in situ hybridization (FISH) [ 12 , 13 ]. Cytogenetic mapping and localization of single-copy gene regions in the genome generally reveal both intra- and interchromosomal rearrangements (i.e., inversions, insertions, deletions or duplications) determined using karyograms [ 9 ]. Moreover, gene loci, which have not yet been mapped within a genome, can be assigned to a specific chromosome within a standardized karyogram [ 14 ].…”

Avian Expression Patterns and Genomic Mapping Implicate Leptin in Digestion and TNF in Immunity, Suggesting That Their Interacting Adipokine Role Has Been Acquired Only in Mammals

“…Double color FISH-TSA protocol was adapted from Krylov et al [66] with minor modifications described in Knytl et al [67]. ABHD16A, CSNK2B, and TNF probes were labeled by Digoxigenin-11-dUTP (Roche, Mannheim, Germany) and hybridized to chromosomal DNA overnight at 37 °C.…”

Divergent subgenome evolution in the allotetraploid frog Xenopus calcaratus

“…In Silurana tetraploids, divergence between the homoeologous a-and bsubgenomes is higher than between the a-subgenome and the genome of diploid X. tropicalis (Evans, 2008;Evans et al, 2015), as expected by allotetraploidy. In Silurana, one large-scale rearrangement has been identified-a nonreciprocal interchromosomal translocation of pericentromeric region between chromosomes 9b and 2a of the tetraploid species X. mellotropicalis (sensu Knytl et al, 2017Knytl et al, , 2018b. This rearrangement was identified using fluorescent in situ hybridization (FISH) in which whole chromosome painting (WCP) probes from X. tropicalis were hybridized to chromosomes of X. mellotropicalis (Zoo-FISH).…”