Dynamics of Replication and Nuclear Localization of the B Chromosome in Kidney Tissue Cells in Astyanax scabripinnis (Teleostei: Characidae)

Abstract

B chromosomes are extra genomic compounds found in different taxonomic groups, including plants and animals. Obtaining patterns of resolutive chromosomal bands is necessary to understand the nuclear organization, variability and nature of B chromosome chromatin and possible transcriptional regions. In this study, we analyzed 35 Astyanax scabripinnis specimens sampled from Fazenda Lavrinha, a stream in the Paraíba do Sul river basin, Brazil. Through the incorporation of the thymidine analog 5¢-bromo-2¢-deoxyuridine (5-BrdU) in vivo, it was possible to recognize the replicating regions of the B chromosome at the beginning of the S phase, differentially characterized in relationship to the regions of late replication. In this perspective, it is possible to suggest that the B chromosome of this species possesses a territory and the chromatin accessible for transcription, especially in the light (i.e., early replicating) bands (p1.1; p1.3; and p2.1 and q1.1, q1.3, q2.1, and q2.2). The latereplicating regions are corresponding to the blocks of constitutive heterochromatin. They show a preferential accumulation of satellite DNA As51. By the use of the fluorochrome chromomycin A3 (CMA3), it was possible to identify GC-rich chromosomal regions, corresponding to late-replicating parts of genome, confirming the revealed data by the replication banding and C-banding. In addition, the analysis by confocal microscopy in kidney cells indicates the location of a peripheral anchorage of this chromosome in the nuclear lamina, reinforcing the idea of downregulation of the associated regions.

Meiotic self-pairing of the Psalidodon (Characiformes, Characidae) iso-B chromosome: A successful perpetuation mechanism

“…Association of two self-paired B chromosomes might not be required to circumvent the MSUC process, because selfpaired B chromosomes do not have unsynapsed regions. The association between two B chromosomes observed here appears to result from their homologous content recognition and/or their physical proximity to specific territories inside the nucleus ( Schemczssen-Graeff et al, 2020 ). When B chromosomes are associated, we observe synaptic regions forming between chromatids ( Figure 4A ), as the employed technique preserves chromosomal associations and avoids the “squash” procedure ( Araya-Jaime et al, 2015 ).…”

GC and Repeats Profiling along Chromosomes—The Future of Fish Compositional Cytogenomics

“…Application of FPG enabled the identification of early and late replicating chromosomal regions with high resolution banding patterns in salmonids [15,16], white sturgeon [16], and eels [17,18]. Less clear patterns after BrdU incorporation were observed on chromosomes of cyprinids [19,20], anastomids [21], ictalurids [22], flatfish [23], pufferfish [24] and characids [25]. The interspecies differences in the resolution of the replication banding may result from different genome composition and the size of chromosomes.…”

B Chromosomes in Psalidodon scabripinnis (Characiformes, Characidae) Species Complex

“…According to 3D cell analysis, the P. scabripinnis B chromosome occupies a peripheral position in the interphase nucleus [ 57 ], which seems to be common in some types of B chromosomes [ 58 ]. This peripheral territory is occupied by chromosomes that tend to be eliminated in hybrids [ 59 ] and other organisms [ 58 ].…”

“…However, if the B chromosome has a specific territory in the dividing cell, it could have a peculiar behavior, such as elimination. The peripheral position of B chromosomes in the nucleus is related to their heterochromatic content and activation status [ 57 ]. Thus, euchromatic B chromosomes in the early stages of evolution could occupy central regions in the nucleus, which could favor their transmission to germ cells, reaching the initial drive.…”

“…Recently, cell lines were obtained from cell cultures of P. paranae with and without B chromosomes at the Laboratory of Fish Biology and Genetics, Botucatu, Brazil, as well as from P. scabripinnis by the Laboratory of Evolutionary Genetics, Ponta-Grossa, Brazil [ 57 ]. These cell lines constitute an important material for cytogenetic, molecular, and functional studies.…”