Molecular and cytogenetic structure of B-chromosomes in Astyanax paranae (Characiformes, Characidae)

Abstract

B chromosomes are genomic elements extra to the standard chromosome complement and occur in many organisms. They may have different origins, including the derivation of autosomal chromosomes and sex chromosomes and even as resulting from crosses between species. The molecular mechanisms that govern the evolution of these segments resemble those of univalent sex chromosomes and may involve gene silencing, heterochromoatinization processes, accumulation of repetitive DNA and transposons. The recent advent of the most effective cytogenetic techniques such as microdissection, a method that enables direct DNA isolation of any chromosomal region associated with the technique of in situ hybridization with fluorescent dyes, has provided new information on the structure and composition of these elements in genomic a significant number of chromosomes carrying organisms B. This study fits into the general program of studies of cytogenetics and molecular genetics of neotropical fish under development at the Laboratory of Fish Biology and Genetics (IBB/UNESP/Botucatu) and has as main objective the cytogenetic analysis at the molecular level of fish species Astyanax paranae. The project will be based on microdissection of B chromosomes (DNA-¼B) of this species, as well as the extraction of genomic DNA (gDNA) and PCR amplification of various repetitive DNA sequences (45S and 5S rDNA, telomeric DNA and genes for histones H1, H3 and H4), and elements retrotransponíveis (Rex1, and Rex3 Rex6) in both types of extracted DNA (gDNA and ¼B-DNA). The development of this work will provide an overview of the relations of the molecular components of B chromosomes with the chromosomes of the complement of A, and chromosomal mapping of multiple DNA repetitive sequences and transposable elements in the chromosomes of the representatives of this group. The main objective of this study will contribute to the knowledge of the molecular content of B chromosomes in a species of Astyanax and generate information to clarify aspects of the origin of this type of segment of DNA in the genome of the species. (AU)