Molecular Analysis of the B Microchromosome in <b><i>Steindachnerina insculpta</i></b> (Characiformes: Curimatidae) by Microdissection

Abstract

B chromosomes are additional elements to standard karyotypes observed in different species of fishes, especially in Curimatidae. However, despite studies demonstrating the occurrence of Bs, little is known about their origin and evolution. To better understand the genomic composition and evolutionary processes involving B chromosomes, microdissection of B microchromosomes in Steindachnerina insculpta was conducted. Chromosome painting revealed the totally hybridized B and markings on A chromosomes both in S. in sculpta and in Cyphocharax spilotus, demonstrating a strong homology between these different species. In specimens of C. modestus, which do not have Bs, the signals were observed on A chromosomes. Cloning and sequencing of some B fragments revealed that the B microchromosome in S. insculpta is composed of repetitive elements, homologous to the DIRS-4 LTR retrotransposon of Xenopus (Silurana) tropicalis. FISH with clone pSi48 with the DIRS-4 retroelement revealed signals on all A chromosomes in the 2 species and also on the B, suggesting the insertion of repetitive elements in these species.

First Record of a B Chromosome in <b><i>Polybia fastidiosuscula</i></b> Saussure (Vespidae) and Investigation of Chromatin Composition Through Microsatellite Mapping

“…Therefore, we suggest that the B chromosome of P. fastidiosuscula originated through fragmentation of a heterochromatic portion (pericentromeric region) of an A chromosome, following the hypothesis of intraspecific origin. Corroborating results were found in fish (Steindachnerina insculpita) [Sampaio et al, 2015], bees (Melipona rufiventris) [Lopes et al, 2008], and wasps (T. albitarse) [Araújo et al, 2000]. Considering that genetic flow occurs between populations of P. fastidiosuscula, the origin of the B chromosome is possibly the same for the 2 colonies studied.…”

“…During an unstable cell division, the fragmentation of a heterochromatic pericentromeric region of an A chromosome may have generated Cytogenet Genome Res 2020;160:711-718 DOI: 10.1159/000513641 a small B chromosome. Mitotic and meiotic analyses in fish species showed that the small size of B chromosomes can reflect instability during cell divisions [Sampaio et al, 2015]. This chromosomal fragmentation may have been a recent event since the B chromosome still has the same heterochromatic characteristics (presence of the TAT microsatellite) as the A chromosome that produced it.…”

First report of B chromosomes in three neotropical thorny catfishes (Siluriformes, Doradidae)

“…The B microchromosomes were described in distinct neotropical fishes, including Schizodon Agassiz, 1829, Astyanax Baird et Girard, 1854, Moenkhausia Eigenmann, 1903, Cyphocharax Fowler, 1906, Steindacnerina Fowler, 1906, Prochilodus Agassiz, 1829, Rhamdia , Bleeker, 1858 Iheringichthys Eigenmann et Norris, 1900, Callichthys Scopoli, 1777, Megalonema Eigenmann, 1912, Pimelodella , Eigenmann et Eigenmann, 1888 and Loricaria Linnaeus, 1758 (Carvalho et al 2008, Lui et al 2009). An interesting hypothesis to explain the origin of these additional genomic elements is the fragmentation in standard karyotype (Sampaio et al 2015). Considering the morphological type, non-Mendelian segregation and low frequencies in mitotic cells, it seems likely that the B chromosomes observed in Platydoras armatulus , Pterodoras granulosus and Ossancora punctata have a recent origin from fragmentation in chromosomes from A complement.…”

Cytogenetic Tools to Study the Biodiversity of Neotropical Fish: From the Classic to the Advent of Cell Culture

“…Many studies search to understand more about the origin, function and evolution of B chromosomes in fishes, since these are considered expendable parasites to supernumerary genome [142]. With the technique of FISH and advances in chromosomal painting, studies using themselves as probes it was possible to examine if there is homology of these extra chromosomes with the normal chromosomes of the karyotype, and from this understand possible answers about the origin and evolution of these chromosomes [51,104,130,143,144].…”