As a typical ciliate, Tetrahymena thermophila is a unicellular eukaryote that exhibits nuclear dimorphism: each cell contains a diploid, germ line micronucleus (MICN) and a polyploid, somatic macronucleus (MACN). During conjugation, when a new MACN differentiates from a mitotic descendant of the diploid fertilization nucleus, the five MICN chromosomes are site-specifically fragmented into 250 t...

Fragile sites are loci of recurrent chromosome breakage in the genome. They are found in organisms ranging from bacteria to humans and are implicated in genome instability, evolution, and cancer. In budding yeast, inactivation of Mec1, a homolog of mammalian ATR, leads to chromosome breakage at fragile sites referred to as replication slow zones (RSZs). RSZs are proposed to be homologous to mam...

Background: Aberrant chromosomes can cause azoospermia but little is known about its molecular mechanism. Our aim is to explore any possible genetic defective to explain a given male infertility. Materials and Methods: An azoopsermic male was identified in a 23 years old male. G-banding and FISH confirmed the karyotype as chromosome insertion (18:7) (q22.1; q36.2q21.11). NGS was performed to an...

FROM time to time one of my colleagues working at a medical school commiserates with me because I spend 40 hr a year lecturing to undergraduates. I always reply that teaching has compelled me to learn a lot of material that I would not have known about had I taught only my specialized subject. These forays into the ‘‘beyond’’ were instrumental in moving my research in new directions. Three arti...

Tetrahymena telomeres are protected by a protein complex composed of Pot1, Tpt1, Pat1, and Pat2. Pot1 binds the 3' overhang and serves multiple roles in telomere maintenance. Here we describe Pot2, a paralog of Pot1 which has evolved a novel function during Tetrahymena sexual reproduction. Pot2 is unnecessary for telomere maintenance during vegetative growth, as the telomere structure is unaffe...

Human lymphocyte cultures were examined for chromosome damage after exposure to ultrasound. Control and treated slides were scored "blind" and showed no evidence of damage due to ultrasound. Neither was there evidence of chromosome damage in blood cultures from six infants whose mothers had ultrasound during pregnancy when compared with that from six infants whose mothers had not. Our results s...

To investigate whether the fragile X syndrome is associated with a generalised chromosomal instability, we compared the frequency and distribution of chromosomal breakage in lymphocytes grown in low folate medium from normal subjects and from patients with the syndrome. Although low folate conditions increased the rate of chromosome breakage, no difference in frequency or distribution of chromo...

Programmed chromosome breakage occurs at 50-200 specific sites in the genome of Tetrahymena thermo-phila during somatic nuclear (macronuclear) differentiation. Previous studies have identified a 15 bp sequence, the Cbs (for chromosome breakage sequence), that is necessary and sufficient to specify these sites. In this study we determined the effects of mutations in the Cbs on its ability to spe...