The forbidden doubling: exploring rare spermatocyte polyploidy in mammals

TL;DR

This study explores rare cases of polyploid spermatocytes in subterranean rodents and identifies meiotic anomalies that may prevent their progression.

Contribution

The study reveals novel meiotic features and potential checkpoint mechanisms in rare polyploid spermatocytes of subterranean rodents.

Findings

Tetraploid spermatocytes show symmetric and asymmetric chromosome quadrivalents with partner-switching.

Altered recombination patterns and chromatin inactivation are observed in these spermatocytes.

Shelterin complexes and LINC connections are present at chromosome ends, similar to normal spermatocytes.

Abstract

We first studied several rare cases of over-diploid spermatocyte emergence using advanced immunocytochemical methods and a cross-species approach in subterranean rodents Ellobius
tancrei (Blasius, 1884), E.
alaicus Vorontsov et al., 1969, E.
talpinus (Pallas, 1770), and Nannospalax
leucodon (Nordmann, 1840) (all belong to the order Rodentia). The tetraploid spermatocytes exhibited specific features during meiotic prophase I, including symmetric and asymmetric chromosome quadrivalents with partner-switching, extended asynapsis, altered recombination patterns, and variable chromatin inactivation. These anomalies suggest that meiotic checkpoints, which are potentially triggered by failed synapsis or incomplete sex chromosome silencing, may act to prevent progression of polyploid spermatocytes. However, the quadrivalents assembled shelterin complexes at chromosome ends, as observed in E.
talpinus, and these ends were connected to the nuclear envelope through the linker of nucleoskeleton and cytoskeleton (LINC) complex, as observed in E.
alaicus, similarly to normal spermatocytes.

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