Characterization of mussel H2A.Z.2: a new H2A.Z variant preferentially expressed in germinal tissues fromMytilus

Abstract

Histones are the fundamental constituents of the eukaryotic chromatin, facilitating the physical organization of DNA in chromosomes and participating in the regulation of its metabolism. The H2A family displays the largest number of variants among core histones, including the renowned H2A.X, macroH2A, H2A.B (Bbd), and H2A.Z. This latter variant is especially interesting because of its regulatory role and its differentiation into 2 functionally divergent variants (H2A.Z.1 and H2A.Z.2), further specializing the structure and function of vertebrate chromatin. In the present work we describe, for the first time, the presence of a second H2A.Z variant (H2A.Z.2) in the genome of a non-vertebrate animal, the mussel Mytilus. The molecular and evolutionary characterization of mussel H2A.Z.1 and H2A.Z.2 histones is consistent with their functional specialization, supported on sequence divergence at promoter and coding regions as well as on varying gene expression patterns. More precisely, the expression of H2A.Z.2 transcripts in gonadal tissue and its potential upregulation in response to genotoxic stress might be mirroring the specialization of this variant in DNA repair. Overall, the findings presented in this work complement recent reports describing the widespread presence of other histone variants across eukaryotes, supporting an ancestral origin and conserved role for histone variants in chromatin.

Effects of Florida Red Tides on histone variant expression and DNA methylation in the Eastern oyster Crassostrea virginica

“…Two of these antibodies constitute commercial products specifically raised against human H2A.X and H2A.Z histones. Their suitability for the study of oyster variants is supported by the high level of evolutionary conservation displayed by these proteins in eukaryotes (Malik and Henikoff, 2003;Eirín-López et al, 2009), as well as by previous reports supporting the experimental application of these antibodies in molluscs (González-Romero et al, 2012;Rivera-Casas et al, 2016b). In the case of macroH2A, an antibody specifically raised against mussel macroH2A (able to specifically detect this variant in invertebrates) was used, further supporting its suitability for oysters (Rivera-Casas et al, 2016a).…”

Epigenetic inheritance and intergenerational effects in mollusks

“…Histones and histone variants have been described in many mollusk species (Drabent et al, 1999;Albig et al, 2003;Li et al, 2006;Rivera-Casas et al, 2016). Protamine-like-type, histone H1-type or protamine-type have also been identified in the sperm or testis of diverse mollusks to replace canonical histones (Eirin-Lopez and Ausio 2009, Mennella et al, 2002, Martinez-Soler et al, 2007.…”

Molecular and Biochemical Methods Useful for the Epigenetic Characterization of Chromatin-Associated Proteins in Bivalve Molluscs

“…Table 1 shows primers designed using this software to amplify histone variants in bivalves annealing in UTR regions, following the indications discussed above (note that some of these primers can be efficiently used in multiple species). It is important to note that species belonging to the genus Mytilus possess at least two different H2A.Z isoforms with specialized roles [H2A.Z.1, which is structurally and functionally equivalent to H2A.Z from other bivalve species, and H2A.Z.2, which is has been specifically identified in Mytilus (Rivera-Casas et al, 2016b )] and that some species (i.e., C. gigas ) have evolved additional H2A.X genes (unpublished work), which will have to be considered when performing PCR experiments. In addition, primers for canonical histones as well as primers annealing in coding regions suitable for RACE or genome walking experiments are indicated in Supplementary Tables 1 , 2 , respectively.…”

“…Based on previous experience, gill, male gonad and sperm tissues produce good amounts of histone proteins following a standard acidic extraction protocol (Shechter et al, 2007 ). In the case of the remaining tissues (muscle, digestive gland, hemolymph, and female gonad), extractions can be optimized by incorporating the modifications detailed below (Gonzalez-Romero et al, 2012b , 2017 ; Rivera-Casas et al, 2016a , b ).…”

“…On one hand, DNA methylation analyses have been conducted in oysters, demonstrating the implication of this mechanism in the regulation of gene expression (Gavery and Roberts, 2010 , 2013 ; Riviere et al, 2013 ; Olson and Roberts, 2014 ; Riviere, 2014 ; Wang et al, 2014 ; Li et al, 2015 ; Saint-Carlier and Riviere, 2015 ; Jiang et al, 2016 ; Tran et al, 2016 ) as well as in responses to environmental stressors (Gonzalez-Romero et al, 2017 ). On the other, our work has provided information about histone diversity and function in the somatic line within this group (Eirin-Lopez et al, 2002 , 2004a ; Gonzalez-Romero et al, 2008 , 2009 , 2012a , b ), including the discovery of histone variants such as macroH2A (Rivera-Casas et al, 2016a ) or H2A.Z.2 (Rivera-Casas et al, 2016b ). In the case of the germinal line, the structural and compositional heterogeneity in the sperm chromatin of bivalves has been elucidated (Ausio, 1986 ), including the evolutionary mechanisms leading to the differentiation of SNBPs from somatic histone H1 (Ausio, 1999 ; Eirin-Lopez et al, 2002 , 2004a , b , 2006a , b ; Gonzalez-Romero et al, 2009 ).…”