Abstract:During the haploid phase of spermatogenesis, spermatids undergo a complex remodeling of the paternal genome involving the finely orchestrated replacement of histones by the highly-basic protamines. The associated striking change in DNA topology is characterized by a transient surge of both single- and double-stranded DNA breaks in the whole population of spermatids which are repaired before spermiation. These transient DNA breaks are now considered part of the normal differentiation program of these cells. Des… Show more
“…Chromatin remodeling in spermatids is one of the most striking changes in nuclear architecture known to the eukaryotic world. This process is associated with transient DNA strand breakage that appears at mid‐spermiogenesis steps but becomes repaired during the final differentiation steps ensuring that no such DNA damage is transferred to the oocyte by the mature sperm [Laberge and Boissonneault, ; Leduc et al., ; Ward, ; Gouraud et al., ]. Chromatin remodeling and the transient surge in DNA strand breaks has been reported in human [Marcon and Boissonneault, ], mouse [Marcon and Boissonneault, ; Leduc et al., ], rat [Meyer‐Ficca et al., ], and drosophila [Rathke et al., ], as well as in the grasshopper [Cabrero et al., ] and in the algae [Wojtczak et al., ] pointing to a highly conserved mechanism with the potential to induce de novo genetic variation through subsequent generations [Grégoire et al., ].…”
Section: Discussionmentioning
confidence: 99%
“…DSBs are apparently part of the normal differentiation program of spermatids since these are observed in the whole population of these cells. DSBs may be induced either enzymatically by topoisomerases or nucleases and/or mechanically, as a result of increased torsional stress [Gouraud et al., ]. In any case, this indicates that the process may represent a window of genetic instability that can, in part, be responsible for the now well‐established male de novo mutation bias [Kong et al., ].…”
Transient DNA breaks and evidence of DNA damage response have recently been reported during the chromatin remodeling process in haploid spermatids, creating a potential window of enhanced genetic instability. We used flow cytometry to achieve separation of differentiating spermatids into four highly purified populations using transgenic mice harboring 160 CAG repeats within exon 1 of the human Huntington disease gene (HTT). Trinucleotic repeat expansion was found to occur immediately following the chromatin remodeling steps, confirming the genetic instability of the process and pointing to the origin of paternal anticipation observed in some trinucleotidic repeats diseases.
“…Chromatin remodeling in spermatids is one of the most striking changes in nuclear architecture known to the eukaryotic world. This process is associated with transient DNA strand breakage that appears at mid‐spermiogenesis steps but becomes repaired during the final differentiation steps ensuring that no such DNA damage is transferred to the oocyte by the mature sperm [Laberge and Boissonneault, ; Leduc et al., ; Ward, ; Gouraud et al., ]. Chromatin remodeling and the transient surge in DNA strand breaks has been reported in human [Marcon and Boissonneault, ], mouse [Marcon and Boissonneault, ; Leduc et al., ], rat [Meyer‐Ficca et al., ], and drosophila [Rathke et al., ], as well as in the grasshopper [Cabrero et al., ] and in the algae [Wojtczak et al., ] pointing to a highly conserved mechanism with the potential to induce de novo genetic variation through subsequent generations [Grégoire et al., ].…”
Section: Discussionmentioning
confidence: 99%
“…DSBs are apparently part of the normal differentiation program of spermatids since these are observed in the whole population of these cells. DSBs may be induced either enzymatically by topoisomerases or nucleases and/or mechanically, as a result of increased torsional stress [Gouraud et al., ]. In any case, this indicates that the process may represent a window of genetic instability that can, in part, be responsible for the now well‐established male de novo mutation bias [Kong et al., ].…”
Transient DNA breaks and evidence of DNA damage response have recently been reported during the chromatin remodeling process in haploid spermatids, creating a potential window of enhanced genetic instability. We used flow cytometry to achieve separation of differentiating spermatids into four highly purified populations using transgenic mice harboring 160 CAG repeats within exon 1 of the human Huntington disease gene (HTT). Trinucleotic repeat expansion was found to occur immediately following the chromatin remodeling steps, confirming the genetic instability of the process and pointing to the origin of paternal anticipation observed in some trinucleotidic repeats diseases.
“…Indeed, the number of mutations inherited by offspring is proportional to paternal age at the time of conception, supporting the hypothesis that the male germline mutation rate is directly correlated with the number of spermatogonial cell divisions34. In addition, there are several mechanistic factors, some of which are unique to males, that may contribute to germline specific mutation5: (a) male germ cells progressively lose DNA repair capacity as they advance through spermatogenesis67; (b) the chromatin remodeling required for the replacement of histone proteins with protamines during spermiogenesis8 may promote additional opportunities for misrepair of endogenous strand breaks9; (c) the process of meiosis provides opportunities to affect nucleotide composition that are unique to germ cells; and, (d) post-meiotic haploid germ cells cannot rely on sister chromatids as templates for homology-based repair mechanisms10. Thus, there are multiple mechanisms unique to male germ cells by which mutations can arise.…”
De novo mutations are implicated in a variety of genetic diseases and arise primarily in the male germline. We investigated whether male germ cells have unique mechanisms for spontaneous or chemically-induced mutation relative to somatic cells using the MutaMouse model. We recovered lacZ transgenes from sperm 42 days after a 28-day exposure to benzo(a)pyrene (BaP, 100 mg/kg/day) to assess mutations arising in dividing spermatogonia. BaP caused a 3.4-fold increase in lacZ mutant frequency over controls which increased to 4.1-fold after clonal correction. We then used next generation sequencing to compare the spontaneous and BaP-induced mutation spectra in sperm and bone marrow. The spontaneous spectrum in sperm had significantly more G:C to A:T transitions and fewer mutations at A:T basepairs than bone marrow. BaP predominantly induced G:C to T:A transversions in both cell types, and both were enriched for mutations at CpG dinucleotides. However, BaP induced significantly more deletions in sperm, but more G:C to A:T transitions and G:C to C:G transversions in bone marrow. Differences in error-prone translesion DNA synthesis polymerases may underlie the observed spectrum differences between sperm and bone marrow. These findings suggest that mutations in sperm can arise via mechanisms that are unique to male germ cells.
“…Gouraud et al (2013) suggested that Spo11 has an additional function as a PM-DSB inducer based on microarray data (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE2736) showing that SPO11 transcription remains high in elongating spermatids in mice. Similarly, RT-PCR showed that SPO11 is transcribed from meiotic prophase (~3 hr) until the post-meiotic stage (6 hr) in Tetrahymena (Figure 6C), suggesting that Spo11 functions in post-meiotic processes.10.7554/eLife.26176.012Figure 6.Spo11 is required for the correct execution of post-meiotic events.( A ) Acetic orcein staining of wild-type (top), ΔSPO11 (middle), and SPO11i (bottom) crosses.…”
Based on observations of markers for DNA lesions, such as phosphorylated histone H2AX (γH2AX) and open DNA ends, it has been suggested that post-meiotic DNA double-strand breaks (PM-DSBs) enable chromatin remodeling during animal spermiogenesis. However, the existence of PM-DSBs is unconfirmed, and the mechanism responsible for their formation is unclear. Here, we report the first direct observation of programmed PM-DSBs via the electrophoretic separation of DSB-generated DNA fragments in the ciliate Tetrahymena thermophila. These PM-DSBs are accompanied by switching from a heterochromatic to euchromatic chromatin structure in the haploid pronucleus. Both a topoisomerase II paralog with exclusive pronuclear expression and Spo11 are prerequisites for PM-DSB induction. Reduced PM-DSB induction blocks euchromatin formation, characterized by histone H3K56 acetylation, leading to a failure in gametic nuclei production. We propose that PM-DSBs are responsible for histone replacement during the reprogramming of generative to undifferentiated progeny nuclei.DOI:
http://dx.doi.org/10.7554/eLife.26176.001
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
