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First published online 24 April 2007
doi: 10.1242/jcs.004945

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Characterization of Spo11-dependent and independent phospho-H2AX foci during meiotic prophase I in the male mouse

¹ Laboratory of Differentiation and Radiobiology of the Gonads, Unit of Gametogenesis and Genotoxicity, Unité Mixte de Recherche-S 566, Commissariat à l'Energie Atomique DSV/IRCM/SEGG/LDRG, F-92265 Fontenay aux Roses, France
² Université Denis Diderot Paris 7, Unité 566, F-92265 Fontenay aux Roses, France
³ Institut National de la Santé et de la Recherche Médicale, Unité 566, F-92265 Fontenay aux Roses, France
⁴ Human Genetic Institut, CNRS UPR 1142, 141 rue de la Cardonille 34396 Montpellier Cedex 5, France
⁵ National Museum of Natural History, CNRS UMR 5202, 16 rue Buffon, 75005 Paris, France

^* Author for correspondence (e-mail: alexandra.chicheportiche{at}cea.fr)

Accepted 20 March 2007

Meiotic DNA double strand breaks (DSBs) are indicated at leptotene by the phosphorylated form of histone H2AX (-H2AX). In contrast to previous studies, we identified on both zygotene and pachytene chromosomes two distinct types of -H2AX foci: multiple small (S) foci located along autosomal synaptonemal complexes (SCs) and larger signals on chromatin loops (L-foci). The S-foci number gradually declined throughout pachytene, in parallel with the repair of DSBs monitored by repair proteins suggesting that S-foci mark DSB repair events. We validated this interpretation by showing the absence of S-foci in Spo11^–/– spermatocytes. By contrast, the L-foci number was very low through pachytene. Based on the analysis of -H2AX labeling after irradiation of spermatocytes, the formation of DSBs clearly induced L-foci formation. Upon DSB repair, these foci appear to be processed and lead to the above mentioned S-foci. The presence of L-foci in wild-type pachytene and diplotene could therefore reflect delayed or unregulated DSB repair events. Interestingly, their distribution was different in Spo11^+/– spermatocytes compared with Spo11^+/+ spermatocytes, where DSB repair might be differently regulated as a response to homeostatic control of crossing-over. The presence of these L-foci in Spo11^–/– spermatocytes raises the interesting possibility of yet uncharacterized alterations in DNA or chromosome structure in Spo11^–/– cells.

Key words: -H2AX, Meiosis, DNA double strand breaks, Spo11

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