Genetic dosage and position effect of small supernumerary marker chromosome (sSMC) in human sperm nuclei in infertile male patient.

Marta Olszewska,Archana Kishore,Maciej Kurpisz,Danuta Zastavna,Elzbieta Wanowska,Nataliya Huleyuk,Ewa Wiland,Alexander N Yatsenko,Andrew P Georgiadis,Mariya Mikula

doi:10.1038/srep17408

Abstract

Chromosomes occupy specific distinct areas in the nucleus of the sperm cell that may be altered in males with disrupted spermatogenesis. Here, we present alterations in the positioning of the human chromosomes 15, 18, X and Y between spermatozoa with the small supernumerary marker chromosome (sSMC; sSMC+) and spermatozoa with normal chromosome complement (sSMC−), for the first time described in the same ejaculate of an infertile, phenotypically normal male patient. Using classical and confocal fluorescent microscopy, the nuclear colocalization of chromosomes 15 and sSMC was analyzed. The molecular cytogenetic characteristics of sSMC delineated the karyotype as 47,XY,+der(15)(pter->p11.2::q11.1->q11.2::p11.2->pter)mat. Analysis of meiotic segregation showed a 1:1 ratio of sSMC+ to sSMC− spermatozoa, while evaluation of sperm aneuploidy status indicated an increased level of chromosome 13, 18, 21 and 22 disomy, up to 7 × (2.7 − 15.1). Sperm chromatin integrity assessment did not reveal any increase in deprotamination in the patient’s sperm chromatin. Importantly, we found significant repositioning of chromosomes X and Y towards the nuclear periphery, where both chromosomes were localized in close proximity to the sSMC. This suggests the possible influence of sSMC/XY colocalization on meiotic chromosome division, resulting in abnormal chromosome segregation, and leading to male infertility in the patient.

Highlights

In infertile carriers, up to 85% of sSMCs originate from acrocentric chromosomes, mostly from chromosome 15, and in more than 50% of cases, the sSMCs are parentally inherited[2]
fluorescence in situ hybridization (FISH) using centromeric probe for chromosome 15 and subtelomeric probe for 15q showed no subtelomere 15q presence in sSMC and at least a twice as small size for the sSMC centromere when compared to the centromere of chromosome 15
The array CGH (aCGH) analysis resulted in 5 copy number variations (CNVs) consisting of one small deletion and 4 amplifications

Summary

Introduction

Up to 85% of sSMCs originate from acrocentric chromosomes, mostly from chromosome 15 (approximately 45%), and in more than 50% of cases, the sSMCs are parentally inherited[2]. In males with decreased sperm parameters (oligozoospermia or oligoasthenoteratozoospermia) sSMC incidence is remarkably elevated (7%)[2] Such disturbances may result from selection mechanisms against additional chromosome content during spermatogenesis, leading to a decrease in the number of gametes, and the incidence of sister chromosomes (demonstrated for de novo sSMCs and in cases with repeated spontaneous abortions), and from some unknown epigenetic factors. It is known, that in the nucleus of diploid cells, chromosomes are localized nonrandomly in chromosome territories (CT). Molecular and cytogenetic methods were used to ascertain the karyotype of the carrier, followed by evaluations of meiotic segregation, sperm aneuploidy level, and chromatin deprotamination status

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