Activation patterns of the nucleolar organizer region in Astyanax scabripinnis populations (Pisces, Characidae)

Abstract

The analysis of the nucleolar organizer regions (NORs) in 4 Astyanax scabripinnis populations collected in the Yukatan stream (population A), Ligeiro stream (population B), Sarandi river (population C) and Agua do Rancho river (population D) indicated the existence of inter- and intrapopulation variations in the number of NORs. The present study also showed a probable mechanism of preferential activation of nucleolar chromosomes, suggesting the presence of main activators as well as different activation patterns in each population. In population A, the large metacentric chromosome was the main nucleolar organizer occurring in about 67% of the cells analyzed, with this population showing the most characteristic NOR pattern compared to the other populations. In populations B, C and D, the main nucleolar organizer chromosomes were a large acrocentric chromosome (65%), a large submetacentric (70%) and a medium-sized submetacentric (71%), respectively.