Nuclear volume differences between balanced and unbalanced spermatozoa in chromosomal translocation carriers

Different Nuclear Architecture in Human Sperm According to Their Morphology

Human sperm parameters serve as a first step in diagnosing male infertility, but not in determining the potential for successful pregnancy during assisted reproductive technologies (ARTs) procedures. Here, we investigated the relationship between sperm head morphology at high magnification, based on strict morphologic criteria, and the nuclear architecture analyzed by fluorescence in situ hybridization (FISH). We included five men. Two of them had an elevated high-magnification morphology score of 6 points (Score 6) indicating high fertility potential, whereas three had a low score of 0 points (Score 0), indicating low fertility potential. We used FISH to study the inter-telomeric distance and the chromosomal territory area of chromosome 1 (Chr. 1). We then compared these two parameters between subjects with high and low scores. FISH data analysis showed that the inter-telomeric distance (ITD) and chromosomal territory area (CTA) of Chr. 1 were significantly higher in subjects with low scores (score 0) than high scores (score 6). Our results suggest that (i) there is a link between nuclear architecture and sperm head abnormalities, particularly vacuoles; and (ii) it is possible to select spermatozoa with normal nuclear architecture, which might indirectly explain the positive ART outcomes observed with this technique.

Chromosomal segregation analysis and HOST-based sperm selection in a complex reciprocal translocation carrier

INTRODUCTION

Complex chromosomal rearrangements (CCRs) involve two or more chromosomes and at least three breakpoints. Due to their complexity, they are associated with a high number of unbalanced gametes, whose fertilization is often incompatible with viable fetal development. Preimplantation genetic diagnosis (PGD) is usually offered to those patients and typically shows modest results considering the high number of unbalanced embryos. We previously showed that a sperm selection process using the hypo-osmotic swelling test (HOST) allows for an 83% reduction in the proportion of unbalanced spermatozoa (US) in male rearrangements carriers. This is the first report of the use of this procedure in a CCR carrier.

CASE DESCRIPTION

We report on the case of a 36-year-old male t(4;7;14)(q12;p21;q11.2) carrier who presented to our center for infertility. Sperm fluorescent in situ hybridization showed an 88% proportion of unbalanced spermatozoa. After hypo-osmotic incubation and selection of spermatozoa with a specific flagellar conformation, the proportion of unbalanced spermatozoa dropped to 15%.

DISCUSSION

In the present case, we show that it is possible to select chromosomally balanced prior to in vitro fertilization in male CCR carriers. This technique has the potential of increasing the proportion of euploid embryos and therefore the chances of healthy pregnancy and birth.

Sperm chromosome segregation of rob(4;16) and rob(4;16)inv(4) in the brown brocket deer (Mazama gouazoubira)

The genus Mazama stands out among the Neotropical deer due to their wide intra and interspecific karyotypic diversification, which is associated with an accentuated chromosomal fragility. There are reports of heterozygous Robertsonian translocation (RT) carriers in a free-range population of Mazama gouazoubira (brown brocket deer), as well as in captive animals of this and other species of the genus. To analyze possible negative impacts of heterozygous chromosome rearrangements on reproductive fitness of the carriers, we performed an analysis of sperm meiotic segregation in four brown brocket bucks, carriers of a rob(4;16), and compared the results with those of a normal buck. We established a reliable FISH and sperm-FISH protocol for the brown brocket deer using bovine (Bos taurus; diploid number, 2n = 60) whole chromosome painting (WCP) and BAC probes. Using BAC probes, we revealed the presence of a paracentric inversion (PAI) of the fused chromosome 4 in two of the four analyzed RT carriers. The mean frequency of normal/balanced sperm in the translocation carriers was significantly lower than in the normal buck (94.78% vs 98.40%). The mean value of total unbalanced spermatozoa was almost doubled in the RT/PAI carriers (6.68%) when compared to RT carriers (3.76%), but the difference was not statistically significant. This study demonstrated the efficiency of FISH with bovine WCP and BAC probes in the characterization of chromosome rearrangements and gametic segregation patterns in brown brocket deer. Our results indicate a low to moderate increase in the rates of unbalanced meiotic segregation products in brown brocket bucks heterozygous for RT and RT/PAIs.

Simple FISH-based evaluation of spermatic nuclear architecture shows an abnormal chromosomal organization in balanced chromosomal rearrangement carriers

INTRODUCTION

Interphasic DNA has a constant three-dimensional conformation, which is particularly striking for spermatic DNA, with distinct chromosomal territories and a constant chromosomal conformation. We hypothesized that this organization is fragile, and that an excess or a lack of chromosomal segments could hinder the genomic structure as a whole.

METHODS

Five human male chromosomal translocation carriers and five controls were included. Spermatic DNA spatial organization was studied, in both balanced and unbalanced spermatozoa, with two-dimensional fluorescent in situ hybridization (FISH) via analysis of chromosomes not implicated in the cases' translocations, compared to that of normal controls. Two parameters were studied: the distance between the two telomeric ends of chromosome 1, and the area of the chromosomal territories of chromosomes 1 and 17.

RESULTS

Sperm FISH analysis of rearrangement carriers revealed changes in the nuclear architecture compared to that of controls. Inter-telomeric distance and chromosomal territories areas were both significantly increased.

DISCUSSION

We show that an excess or lack of chromosomal segments can hinder the normal spatial nuclear architecture in sperm. These results show that nuclear architecture is a fragile assembly, and that local chromosomal abnormalities may impact the nucleus as a whole. This suggests a potential avenue for selection of spermatozoa prior to in vitro fertilization, not only in rearrangement carriers but also in the infertile population at large. Furthermore, we suggest that 2D-FISH could possibly be a useful tool in assessing spermatic nuclear organization in a way to evaluate male fertility.