Organization and Distribution of Repetitive DNA Classes in the <i>Cichla kelberi</i> and <i>Cichla piquiti</i> Genome

Abstract

The family Cichlidae is considered a non-Ostariophysi freshwater fish family with diverse and geographical distribution wide in the world; nevertheless there is scarce cytogenetic information for the group. Accordingly, we aim to characterize Cichla kelberi and Cichla piquiti specimens by conventional cytogenetic (Giemsa, Ag-NOR, Banding C) and cyto-molecular (FISH with 5S, 18S, Rag1, Rex3, Rex6 and telomeric probes) markers. In both species, cytogenetic analyses showed 2n=48 chromosomes (all of the subtelocentric/acrocentric type), NORs located terminally on the second chromosome pair and heterochromatic blocks in the centromeres of some chromosomes. The location of the 18S ribosomal gene confirms what was previously observed with impregnation with silver nitrate, while the 5S rDNA is in interstitial position on the third chromosome pair. The telomeric probe, as expected, was present only in telomeric regions of all chromosomes. The Rag1, transposable elements, Rex3 and Rex6 present dispersed sites throughout most of the chromosomes, not characterizing a definite pattern of distribution. Thus, the present study adds relevant information about the cytogenetics and behavior of different repetitive DNA families in C. kelberi and C. piquiti, which require future studies to understand the gene behavior and evolution in Neotropical fish, especially in the genus Cichla.

Rex Retroelements and Teleost Genomes: An Overview

“…Moreover, regarding chromosomal arrangements, Rex retroelements can be widely spread among chromosomes [ 39 , 40 , 41 , 45 , 47 , 51 , 52 , 54 ] or preferentially located in specific chromosomal regions and/or chromosome pairs [ 26 , 36 , 38 , 39 , 40 , 42 , 44 , 45 , 48 , 49 , 51 ].…”

“…Concerning Cichliformes, in the 18 species investigated, Rex retroelements showed a wide variability in the hybridization signal distribution. Indeed, three species exhibited a spread distribution of Rex retroelements [ 43 , 47 ], four a compartmentalization in specific chromosome pairs [ 43 , 45 , 48 ], and eight a pericentromeric heterochromatic localization of most chromosomes [ 44 , 49 ]. Focusing on Nototheniidae family belonging to Perciformes, Rex1 and Rex3 signals were spread all over the chromosomes, except for N. coriiceps , in which a pericentromeric compartmentalization of Rex retroelements has been reported [ 51 ].…”

“…C. kelberi was also analyzed by de Freitas Mourão and colleagues [ 47 ] together with the congeneric species C. piquitii, evidencing a spread distribution of Rex elements on the majority of chromosomes in contrast with findings reported by Teixeira et al [ 48 ] and Valente et al [ 44 ].…”

Mobile Elements in Ray-Finned Fish Genomes

“…Rex6 is a member of the R4 family [ 171 ] of non-LTR retrotransposons and it encodes a specific type of endonuclease, closely related to the type IIS restriction enzymes isolated from trypanosomes, nematodes, and arthropods [ 172 ]. Rex6 elements have been found in many teleost orders: Anguilliformes [ 55 , 59 ], Beloniformes [ 60 , 61 ], Carangiformes [ 129 ], Centrarchiformes [ 59 ], Characiformes [ 79 , 82 , 149 , 173 , 174 , 175 ], Cichliformes [ 60 , 132 , 133 , 136 , 176 , 177 , 178 , 179 , 180 ], Cypriniformes [ 59 ], Cyprinodontiformes [ 59 ], Esociformes [ 60 ], Perciformes [ 60 , 181 ], Salmoniformes [ 60 ], Siluriformes [ 174 , 182 , 183 , 184 ], and Tetraodontiformes [ 60 , 61 , 134 , 142 , 185 ].…”