The stability of telomereless chromosome fragments in adult androgenetic rainbow trout

Abstract

SUMMARY The study provides new data on the stability of gamma radiation-induced chromosome fragments of a putative maternal nuclear genome in an androgenetic vertebrate, rainbow trout (Oncorhynchus mykiss Walbaum). The fragments were found in five of 16 examined individuals and they were mostly centromeric parts of metacentric or subtelocentric chromosomes. Chromosome fragments were identical in all cells of a given androgenetic individual,indicating that segregation of chromosome fragments is active from the early cell divisions. Most of the fragments were telomereless, i.e. they had no telomeric sequences on their ends. This shows that telomeres are not necessary for stability of chromosomal structures in a vertebrate genome. In one individual, the interstitial telomeric sites were found in chromosomes, which could be the effect of joining chromosome fragments.

FISH and DAPI staining of the synaptonemal complex of the Nile tilapia (Oreochromis niloticus) allow orientation of the unpaired region of bivalent 1 observed during early pachytene

“…This suggested that these chromosomal regions are rich in relatively small AT-rich clusters, visible only on extended loops of DNA. DAPI-positive regions in pericentromeric positions have been previously identified on mitotic chromosomes in several fish species and the intensity and number of the signals vary from few and very weak (Ocalewicz, 2005) to very strong and localized on most (Ocalewicz et al, 2004) or all of the chromosomes (Fischer et al, 2000). Moreover, DAPI positive signals can be seen in interstitial positions on fish chromosomes (Ocalewicz et al, 2007).…”

Genetic basis of differences in myxospore count between whirling disease-resistant and -susceptible strains of rainbow trout

“…The assumption of independent assortment among loci was tested using haploid chromosome number (N = 29;Hartley & Horne 1982, Thorgaard 1983, Ocalewicz et al 2004) and genetic linkage maps (Young et al 1998, Sakamoto et al 2000, Nichols et al. 2003 for rainbow trout.…”

“…The assumption of independent assortment among loci was tested using haploid chromosome number (N = 29; Hartley & Horne 1982, Thorgaard 1983, Ocalewicz et al 2004) and genetic linkage maps (Young et al 1998, Sakamoto et al 2000, Nichols et al 2003) for rainbow trout. The average haploid chromosome number of 29 was chosen as representative for the rainbow trout population used in this study; however, due to polymorphism (Thorgaard 1983), haploid chromosome number in rainbow trout is known to vary from this average (Guyomard et al 2006).…”

Genomic Distribution of Telomeric DNA Sequences – What Do We Learn from Fish About Telomere Evolution?

“…Insufficient dose of radiation results in incomplete inactivation of maternal nuclear genome. Undamaged pieces of the irradiated genome in the forms of chromosome fragments were observed in the androgenetic alevins and adult fish (Parsons and Thorgaard, 1985;Ocalewicz et al 2004a). In the course of partial inactivation of maternal chromosomes, different chromosome fragments may be provided; acentric terminal fragments with telomeric region at only one end or without any telomeres and centric incomplete chromosomes without telomeres, or telomere at only one arm.…”

“…Tetraploidization event in the Salmonid ancestor has been followed by the rediploidization process leading to the recovery of disomic segregation and performed by the various chromosomal rearrangements like fusions and inversions (Phillips and Rab, 2001). On top of that, androgenetic fish developing in the gamma/X radiation-enucleated eggs seem to be promising models for studying the role of telomerase in the fish DNA Double Strand Breaks repair machinery (Ocalewicz et al, 2004a). …”