Neo-sex chromosomes of Ronderosia bergi: New insights on molecular sex chromosomes evolution in grasshoppers

PALACIOS-GIMENEZ OCTAVIO M, MARTI DARDO A, CABRAL-DE-MELLO DIOGO C.

Guarujá

Simposio; III Reunión Brasilera de Citogenética, IV Simposio Latinoamericano de Citogenética y Evolución; 2013

SBG

The accumulation of repetitive DNAs is common during differentiation of neo-sex chromosomes being more evident after recombination restriction. Aiming the understanding of sex-chromosome evolution in grasshoppers, we analyze the derived sex-chromosome neo-XY of Ronderosia bergi through classical cytogenetic and FISH for multigene families, C0 t-1 DNA fraction, telomeric repeat, microsatellites and microdissection chromosomes. Moreover, multigene families for 5S rDNA, U1/U2 snDNA were isolated through PCR specifically from microdissection of neo-X and neo-Y and female genomic DNA. Ronderosia bergi presented 2n♂=22+neo-XY, being the neo-Y telocentric and the neo-X metacentric, product of an X-autosome Robertsonian fusion. C-positive blocks were observed in all chromosomes, with the neo-Y entirely heterochromatic; G+C-rich blocks were evidenced in the pairs 6, 7 and 9. The mapping of multigene families (18S/5S rDNAs, U1/U2 snRNAs and H3 histone) revealed the presence of U2 snRNA in the Y chromosome besides the pair 1, while the other multigene families were exclusively located in autosomes; 18S rDNA (pairs 6, 9), 5S rDNA (pairs 2-5), H3 histone (pair 7) and U1 snRNA (pairs 3, 4). C0t-1 DNA showed positive signals in the centromeric regions of the pairs 1-4, 9 and neo-X, additionally pair 3 showed a sub-terminal block. Telomeric probe revealed terminal signals in all chromosomes, without interstitial signals in the metacentric neo-X. The microsatellites (AG)30, (GAC)10, (GAG)10, (CAA)10 and (GATA)8 were scattered in all chromosomes; (TA)15 and (AG)10 were more evident in the centromeric and sub-terminal regions of neo-Y and pair 8, respectively. The (CAT)10 was more evident in the centromeric region of neo-X and pair 5, and centromeric/proximal in pair 4. The probe obtained from microdissected neo-X revealed positive signals in the centromere of neo-X and pairs 4, 5, while neo-Y probe painted exclusively the entire neo-Y. The PCR using the microdissected neo-X and neo-Y amplified the 5S rDNA of neo-X and neo-Y, and U1/U2 snRNAs from neo-Y, indicating the presence of these repeats in the sex chromosomes, not observed by FISH. The sequence analysis for the three multigene families revealed homogenization among autosomes and neo-Y for U2 snRNA, divergence for U1 snRNA between the neo-Y and autosomes and mixed (diversification/homogenization) among neo-X, neo-Y and autosomes for 5S rDNA. Ours results showed a highly differentiated neo-Y due Rb-fusion, inversion, heterochromatinization and accumulation of repetitive DNAs in non-recombining regions after chromosomal rearrangement, besides different patterns of diversification/homogenization between sex chromosomes and autosomes for multigene families, bringing new insights of sex-chromosome evolution in grasshoppers.