Microdissection and complete sequencing of B chromosomes in fish applied to evolutionary and functional studies

Author(s)

Ricardo Utsunomia

• Document type: Doctoral Thesis
• Press: Botucatu. 2016-09-22.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
• Defense date: 2016-02-19
• Advisor: Fausto Foresti

Abstract

In the present study, two populations of the fish species Moenkhausia sanctaefilomenae, one collected at the Batalha river, Bauru-SP (Tietê river basin) and the other collected at the Novo river, Ocauçu-SP (Paranapanema river basin), were analyzed through classical and molecular cytogenetic techniques. Besides, Illumina HiSeq2000 sequencing was performed for both genomes and for one microdissected B-variant. Results obtained revealed that all the individuals from the Batalha river show from 0 to 6 B chromosomes per cell, while the specimens from Novo river did not show any supernumerary chromosomes. One must note that the B chromosomes found in the Batalha river might be classified into 2 variants, one euchromatic (B1) and present in all the population, and another heterochromatic (B2) with lower prevalence. Fluorescence in situ hybridization (FISH) using repetitive DNA probes revealed that both B-types showed 18S rDNA, H3 histone and MS3 and MS7 satDNAs. Interestingly, the only between-variant difference was the abundance of 18S rDNA. Sequence analysis revealed that the B1 variant is older than B2, although both variants seem to be derived from the same autosomal pair. Notably, selection seems to be relaxed for H3.3 histone genes located on the B chromosomes. For a better knowledge about the genomic content of B chromosomes, a microdissected library of B1 variant was sequenced and data obtained revealed an intense accumulation of transposable elements in this supernumerary, in addition to single copy genes, that are present in different linkage groups of Astyanax mexicanus genome. These results will be used for future evolutionary and functional studies about B chromosomes. The combined approach of chromosomal and molecular methods was used to better understand evolutionary issues of supernumerary chromosomes in Neotropical fish. (AU)

• FAPESP's process: 13/00953-8 - Microdissection and complete sequencing of B chromosomes in fish applied to functional and evolutionary studies
• Grantee: Ricardo Utsunomia
• Support Opportunities: Scholarships in Brazil - Doctorate