Meiotic Synapsis Proceeds from a Limited Number of Subtelomeric Sites in the Human Male

Abstract

The formation of the synaptonemal complex (SC) is a crucial early step in the meiotic process, but relatively little is known about the establishment of the human SC. Accordingly, we recently initiated a study of synapsis in the human male, combining immunofluorescence and fluorescence in situ hybridization methodologies to analyze prophase spermatocytes from a series of control individuals. Our results indicate that synapsis is a tightly regulated process, with relatively little variation among individuals. On nonacrocentric chromosomes, there are two synaptic initiation sites, one on the distal short arm and one on the distal long arm, whereas acrocentric chromosomes exhibit a single site on the distal long arm. For both types of chromosomes, synapsis then proceeds toward the centromere, with little evidence that specific p- or q-arm sequences affect the process. However, the centromere appears to have an inhibitory effect on synapsis--that is, when one arm of a nonacrocentric chromosome is "zippered up" before the other, the centromere acts as a barrier to further movement from that arm.

DNA double strand break repair, chromosome synapsis and transcriptional silencing in meiosis

“…1 However, in mammals this may not be the case, since cytological observations have indicated that synapsis proceeds from the telomeric ends of the paired homologous chromosomes in humans. 2 Telomeres function during the initial phase of chromosome pairing in both yeast and mammals. During this phase, all telomeres cluster on the nuclear membrane, while the chromosomal arms loop towards the center of the nucleus, forming the transient bouquet stage.…”

Regulating double-stranded DNA break repair towards crossover or non-crossover during mammalian meiosis

“…Several arguments have led to the proposition that SIC are located at the same sites where crossovers will form (Henderson & Keeney 2005). In humans, analysis of synapsis initiation has indeed suggested a limited number of sites preferentially located near sub-telomeric regions in correlation with CO density (Brown et al 2005).…”

Human Male Meiosis and Sperm Aneuploidies

“…Furthermore it has been seen that the centromere avoids spreading the synapsis from q-arm to p-arm and vice versa (Brown et al, 2005). Fig.…”

“…Several studies of human chromosomes have shown that at least one crossover occurs in each arm, except in short arms of acrocentric chromosomes, where crossovers occur infrequently. Further, the existence of a crossover inhibits the formation of another in a nearby region, a phenomenon known as "interference" (Brown et al, 2005; reviewed by Lynn et al, 2004;Sun et al, 2004a).…”