Chromatin configuration and epigenetic landscape at the sex chromosome bivalent during equine spermatogenesis |
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Authors: | Claudia Baumann Christopher M Daly Sue M McDonnell Maria M Viveiros Rabindranath De La Fuente |
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Institution: | (1) Female Germ Cell Biology Group, Department of Clinical Studies, University of Pennsylvania, New Bolton Center, 382 West Street Road, Kennett Square, PA 19348, USA;(2) Department of Animal Biology, Center for Animal Transgenesis and Germ Cell Research, University of Pennsylvania, New Bolton Center, 382 West Street Road, Kennett Square, PA 19348, USA;(3) Section of Reproduction, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, 382 West Street Road, Kennett Square, PA 19348, USA;(4) Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, 501 D.W. Brooks Drive, Athens, GA 30605, USA; |
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Abstract: | Pairing of the sex chromosomes during mammalian meiosis is characterized by the formation of a unique heterochromatin structure
at the XY body. The mechanisms underlying the formation of this nuclear domain are reportedly highly conserved from marsupials
to mammals. In this study, we demonstrate that in contrast to all eutherian species studied to date, partial synapsis of the
heterologous sex chromosomes during pachytene stage in the horse is not associated with the formation of a typical macrochromatin
domain at the XY body. While phosphorylated histone H2AX (γH2AX) and macroH2A1.2 are present as a diffuse signal over the
entire macrochromatin domain in mouse pachytene spermatocytes, γH2AX, macroH2A1.2, and the cohesin subunit SMC3 are preferentially
enriched at meiotic sex chromosome cores in equine spermatocytes. Moreover, although several histone modifications associated
with this nuclear domain in the mouse such as H3K4me2 and ubH2A are conspicuously absent in the equine XY body, prominent
RNA polymerase II foci persist at the sex chromosomes. Thus, the localization of key marker proteins and histone modifications
associated with the XY body in the horse differs significantly from all other mammalian systems described. These results demonstrate
that the epigenetic landscape and heterochromatinization of the equine XY body might be regulated by alternative mechanisms
and that some features of XY body formation may be evolutionary divergent in the domestic horse. We propose equine spermatogenesis
as a unique model system for the study of the regulatory networks leading to the epigenetic control of gene expression during
XY body formation. |
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