B chromosome: meiotic behavior and segregation patterns in Astatotilapia latifasciata

Author(s)

Natália Bortholazzi Venturelli

• Document type: Doctoral Thesis
• Press: Botucatu. 2018-05-07.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
• Defense date: 2018-03-09
• Advisor: Cesar Martins

Abstract

The cells have a regular set of chromosomes known as A chromosomes. However, there are extra chromosomes and one of them is the extra elements called B-chromosomes (Bs) that occurs in a wide variety of eukaryotes including fungi, plants and animals. Since its description, Bs have attracted the attention of the researchers. To be classified as a B, some characteristics must be present such as: distinct morphology of A chromosomes, number of copy can vary between the individuals bearing it, they are often heterochromatic, they are not homologous to the A complement set, they did not pare or recombine with As, and often exhibit non-Mendelian heritage. B chromosomes have been described in several vertebrates, including the cichlid fish Astatotilapia latifasciata, native to Kyoga and Nawampasa lakes, satellite lakes to Victoria lake in East Africa, which has 44 chromosomes and the presence of 1 to 2 B chromosomes. This work aimed to investigate the meiotic behavior of B chromosomes via immunostaining with specific antibodies against synaptonemic complex proteins, coesins and histone modifications; directed crosses between males and females with and without B; and gene expression analysis: synaptonemal complex protein 2-like, mitochondrial cardiolipin hydrolase-like, separin-like, tubulin beta-1 chain-like and kinesin-like. Immunostaining with antibodies H3K27me3 and H3K4me3 showed a global distribution in the pachytene phase. The H3K9ac antibody was dispersed throughout all the regions of the interphase chromatin and maintained until the pachytene, where it is associated with the synaptonemic complex. Using structured lighting super-resolution (SIM) technology, we observed, with double of the resolution, specific antibodies against coesins and proteins of the synaptonemic complex. All chromosomes, including B, present the regular structure of the synaptonemic complex, which are fundamental to guarantee the meiotic progression and maintenance of the B chromosome in the cell. The selfpairing hypothesis of the investigated chromosome B has been confirmed and this self-pairing is a mechanism that allows the B chromosome to be maintained in the cells during the meiotic division. From the data of directed crossings and statistical analysis we can infer that there is a meiotic drive acting in the species A. latifasciata, being this more evidentin females. In addition, the expression of some intact B chromosome genes is more intense in females, evidencing the involvement of these genes in the control of the meiotic transmission of chromosome B. (AU)

• FAPESP's process: 13/25234-4 - Meiotic behavior of B chromosomes in the cichlid fish Astatotilapia latifasciata, based on synaptonemal complex and immunocytogenetic analyses
• Grantee: Natália Bortholazzi Venturelli
• Support Opportunities: Scholarships in Brazil - Doctorate