Atm Inactivation Results in Aberrant Telomere Clustering during Meiotic Prophase

Abstract

A-T (ataxia telangiectasia) individuals frequently display gonadal atrophy, and Atm؊/؊ mice show spermatogenic failure due to arrest at prophase of meiosis I. Chromosomal movements take place during meiotic prophase, with telomeres congregating on the nuclear envelope to transiently form a cluster during the leptotene/zygotene transition (bouquet arrangement). Since the ATM protein has been implicated in telomere metabolism of somatic cells, we have set out to investigate the effects of Atm inactivation on meiotic telomere behavior. Fluorescent in situ hybridization and synaptonemal complex (SC) immunostaining of structurally preserved spermatocytes I revealed that telomere clustering occurs aberrantly in Atm ؊/؊ mice. Numerous spermatocytes of Atm ؊/؊ mice displayed locally accumulated telomeres with stretches of SC near the clustered chromosome ends. This contrasted with spermatogenesis of normal mice, where only a few leptotene/zygotene spermatocytes I with clustered telomeres were detected. Pachytene nuclei, which were much more abundant in normal mice, displayed telomeres scattered over the nuclear periphery. It appears that the timing and occurrence of chromosome polarization is altered in Atm ؊/؊ mice. When we examined telomere-nuclear matrix interactions in spermatocytes I, a significant difference was observed in the ratio of soluble versus matrixassociated telomeric DNA sequences between meiocytes of Atm ؊/؊ and control mice. We propose that the severe disruption of spermatogenesis during early prophase I in the absence of functional Atm may be partly due to altered interactions of telomeres with the nuclear matrix and distorted meiotic telomere clustering.Ataxia telangiectasia (A-T) is an autosomal recessive disorder characterized by progressive neurological degeneration, premature aging, growth retardation, specific immunodeficiencies, telangiectasia, high sensitivity to ionizing radiation, genomic instability, cancer progression, and gonadal atrophy (9, 31). Cells derived from A-T individuals exhibit a variety of abnormalities in culture such as cytoskeletal defect, hypersensitivity to ionizing radiation, and higher requirement for serum growth factors (51, 78). They also show a prominent chromatin defect at chromosome ends in the form of chromosome endto-end associations (also known as telomeric associations) seen at metaphase (38,61,63,89). Chromosome end associations correlate with genomic instability and carcinogenicity (18,61,63) and involve telomeres (48,55). Telomeres consist of repetitive (TTAGGG) DNA and proteins which protect chromosome ends from exonucleolytic attack, fusion, and incomplete replication (7, 98). Telomere erosion in a variety of cancers and cell lines has been found to lead to chromosome end associations that could contribute to genomic instability and gene amplification (18,47,60,82).It has been suggested that mammalian terminal (TTAGG G) n repeat arrays interact with the nuclear matrix (19, 44). Whether ATM gene effectors influence the interaction of telomeres with the nu...

Human Exonuclease 5 Is a Novel Sliding Exonuclease Required for Genome Stability

“…Cells were fixed in 2% paraformaldehyde for 15 min, washed in 1ϫ PBS, permeabilized for 5 min on ice in 0.2% Triton X-100, and blocked in PBS with 1% bovine serum albumin. The procedure used for immunostaining is the same as that described previously (17)(18)(19).…”

ATM function and telomere stability

“…Interestingly, it has been shown that ATM function in¯uences on the fraction of telomeres anchored to the nuclear matrix (Smilenov et al, 1999). In somatic as well as germ cells de®cient in ATM function, more than 80% of the telomeric DNA is attached to the nuclear matrix, whereas in control cells about 50% is attached (Smilenov et al, 1999;Pandita et al, 1999). These results suggest that the major portion of telomeres in A-T cells is associated with the nuclear matrix.…”

H2AX: the histone guardian of the genome

“…This clustering of telomeres is thought to insure proper homolog pairing and synapsis of the homolog axes [60][61][62]. Interestingly both ATM [63] and more recently H2AX [29] have been shown to regulate the persistence of the telomere bouquet. The exit from the bouquet stage may therefore be coupled to the completion of the repair of meiotic DSBs.…”