Repetitive DNA Content of B Chromosomes in the Cichlid Fish Astatotilapia latifasciata

B chromosomes (B) are supernumerary elements, complementary and non-homologous to the regular (A) set of chromosomes. B chromosomes are enriched with repetitive elements and can carry functional genes. The cichlid fish Astatotilapia latifasciata can harbors 1 or 2 B chromosomes with high repetitive elements content, found using classical cytogenetics analysis. Next generation sequencing data is being applied to further characterize these elements and understand their role on the formation and perpetuation of B chromosome. Comparative analysis using graph based clustering, through the RepeatExplorer pipeline, was performed on Illumina sequencing reads from individuals without B chromosomes (0B) and with 2 B chromosomes (2B), in search of major classes of repetitive elements. Using contig data from RepeatExplorer, probes for Fluorescent in situ Hybridization (FISH) were constructed for candidate elements and mapped on chromosome preparations from individuals with 1B. Primers for Real-Time PCR (qPCR) were designed for mapped elements to inquire their relative quantification. Bioinformatics analysis revealed various transposable elements (TE) expanded on the B chromosome, specially a Bel/Pao like and a Gypsy like TEs, which are mainly found on the additional chromosome. FISH mapping showed strong signal from element probes mainly on the B chromosome and qPCR confirmed a higher element copy number on B positive individuals. Results suggest that some TEs are more abundant on the B chromosome of Astatotilapia latifasciata than on the A set. Transposition and duplication events can help explain the perpetuation and constitution of B chromosomes on the species.

Financial support: FAPESP, CAPES, CNPq