IDENTIFICAÇÃO E CARACTERIZAÇÃO DE ELEMENTOS RETROTRANSPONÍVEIS NO GENOMA DE ESPÉCIES DE ECHIMYIDAE (MAMMALIA: RODENTIA)

Abstract

Transposable Elements (TEs) have been considered to be of fundamental importance for evolutionary divergence in mammals. Therefore, for the development of this research, rodents from the Echimyidae family (Gray 1825) were selected as study material, due to their diversity in taxonomic, ecological, morphological, adaptive and cytogenetic terms. Cytogenetic and molecular techniques were used to isolate, purify, clone and characterize, through sequencing, the sequences of the retroelements LINE-L1, SINE-B1, SINE-B4, SINE-MAR and SINE-THER that were used as probes for hybridization in metaphase chromosomes. The objective was to evaluate the evolutionary dynamics of retrotransposable elements between species, representatives of the different subfamilies of Echimyidae, namely: Dactylomys sp. (Dactylomyinae); Isothrix sp., Makalata sp. (Echimyinae); Proechimys sp., Mesomys sp., Thrichomys sp. and Trynomys sp. (Eumysopinae). The mapping of LINE-L1 and SINE-B1 in the genome of the species demonstrated that these retroelements remained in the karyotypes, in non-homeologous chromosomes. The similarities of L1 and B1 signals in non-homeologous chromosome pairs, mainly in centromeric and/or pericentromeric regions, indicate that rearrangements occurred during the diversification of karyotypes. These data revealed signal homeology of L1 and B1 sequences in Proechimys comprising four groups: (1) P. longicaudatus (2n = 28/FN = 46) and P. cuvieri (2n = 28/FN = 46), (2) P. guyannensis (2n = 46/FN = 50) and P. guyannensis (2n = 38/FN = 52), (3) P. gardneri (2n = 40/FN = 54), and (4) P. echinothrix ( 2n = 32/FN = 58). The cladogram proposed for the L1 and B1 sequences, composed of five subgroups with different degrees of similarity, reflects some of the taxonomic relationships proposed in the literature, for Echimyidae: D. dactylinus (2n = 94/FN = 134) and M. didelphoides ( 2n = 72/FN = 132) (tree spiny rats) were grouped together, as were M. hispidus (2n = 60/FN = 116) and I. pagurus (2n = 22/FN = 38) (tree spiny rats), T paratus (2n = 58/FN = 112), T. apereoides (2n = 28/FN = 50), and P. guyannensis (2n = 46/FN = 50) (spiny land rats). The distribution of L1 and B1 in fiber-FISH confirmed possible rearrangements, due to the diversification found in the fibers of different species. L1 and/or B1 blocks were coincident with constitutive heterochromatin (HC), in interstitial, terminal and/or centromeric regions of some chromosome pairs. The alternation of L1 and/or B1 in the centromeric heterochromatic sites of sex chromosomes may be associated with competition between copies of TEs in the genome. The presence of L1 and/or B1 blocks coinciding with HC may be associated with genome plasticity and chromatin remodeling. Already, TEs in regulatory regions may have been co-opted to enhance this effect, as demonstrated in this study with sites in the nucleolus organizing region (RON) in the Proechimys genome, as well as in all species, blocks of 18S rDNA were coincident with blocks of L1 in one of the homologues. The wide distribution of different SINEs in chromosomes demonstrated differentiation of these retroelements in Proechimys species. The signal from SINEs B4 and MAR was more explosive than that from SINEs B1 and THER, and involved centromeric/pericentromeric and terminal regions in most chromosomes. This explosion of SINEs is explained by the fact that these elements appear again many times in evolution. The SINEs signal was distributed in a varied and specific way in the genome of Proechimys species and may be related to the karyotypic evolution of this genus. The clusters formed from the LINE-L1 and SINE-B1 sequences suggest that these retroelements may be correlated with differentiation patterns in this family and may provide insights into the evolutionary relationships between taxa and TEs