Iouzalen N et al. (1996), H2A.ZI, a new variant histone expressed during ...

XB-ART-17564

Nucleic Acids Res 1996 Oct 15;2420:3947-52. doi: 10.1093/nar/24.20.3947.

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H2A.ZI, a new variant histone expressed during Xenopus early development exhibits several distinct features from the core histone H2A.

Iouzalen N , Moreau J , Méchali M .

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We have isolated from a subtractive cDNA library of Xenopus laevis a novel transcript, H2A.ZI, which belongs to the H2A.Z variant gene family. Characterization of its expression during oogenesis and development shows significant differences from the expression of the core histone H2A. First, H2A.ZI mRNA is mainly detected only during oogenesis and after the midblastula transition, whereas H2A is constitutively expressed, at much higher levels, throughout embryonic growth. Second, in contrast with H2A, the variant H2A.ZI is polyadenylated during development. Third, expression of H2A.ZI is uncoupled from the S phase after gastrula, whereas synthesis of the core histone H2A mRNA is tightly controlled to DNA replication. Interestingly, H2A.ZI is less charged in the N-terminal tail which is crucial for chromatin-mediated repression. The characteristics of H2A.ZI suggest that its incorporation into nucleosomes would lead to a chromatin structure more competent for gene expression during development.

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Species referenced: Xenopus laevis
Genes referenced: chrd h2ac21 h2az1 h3-5 hvcn1

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	Figure 1. Deduced amino acid sequence of Xenopus H2A.Zl compared with other members of the H2A family. The deduced Xenopus H2A.Zl protein is shown and compared with the sequences of the human, bovine and rat H2A.Z (3), calf thymus H2A.Z (45), chicken H2A.F (4), Drosophila H2A.vD (5), sea urchin H2A.F/Z (6), Tetrahymena hv1 (7) and Xenopus H2A core histone (46). Dots represent residues that are identical to the corresponding residues in H2A.Zl. Dashes indicate the absence of amino acid residues at the corresponding position. Highly dissimilar residues between H2A.Zl and other H2A.Z variants are denoted by a black background. Arrows indicate two amino acids which change the net charge.
	Figure 2. Expression during development of the non variant H2A.Zl mRNA compared with the core histone H2A. (A) Ten mg of total RNA extracted from oocytes and embryos were loaded and electrophoresed in a formaldehyde gel containing 1.5% agarose. On the right part of the gel, known quantities (pg) of cloned fragments containing H2A.Zl or H2A sequences were loaded. (B) Poly(A)+ and poly(A)– fractions were obtained from total RNA by passage over oligo (dT)-cellulose. Northern blots were probed with a H2A.Zl DNA probe (1 × 106 c.p.m./ml) or a H2A DNA probe (1 × 106 c.p.m./ml). The 18S cDNA probe (2 × 104 c.p.m./ml) was used to compare the equivalence of RNA loaded on each lane. The exposure times were 2 days for H2A.Zl and H2A and 3 h for the 18S RNA.
	Figure 3. Spatial expression pattern of H2A.Zl and H2A mRNAs in stage 25/26 Xenopus embryos. Whole mount in situ hybridization was used as described in Materials and Methods. Antisense H2A (A), H2A.Zl (B) and Chordin (C) probe hybridization signals are shown. No hybridization signal was detected in embryo probed with a sense probe (D).
	Figure 4. H2A.Zl expression is uncoupled from DNA replication in post gastrula embryos. Developing embryos from a single sibling group were divided into a control group and an aphidicolin (125 mg/ml) group at the early gastrula stage (stage 10). Undigested genomic DNA and total RNA were prepared from the same embryos collected at the indicate times (0 h: stage 10; 2 h: stage 11; 18 h: stage 19; 22 h stage 24/25) after transfer into the aphidicolin-containing media. (A) Products analyzed on a 0.6% agarose gel stained with ethidium bromide to detect genomic DNA and rRNAs. (B) The gel was blotted and successively hybridized with H2A.Zl, H2A and 18S cDNA probes.

References [+] :

Adamson, Histone synthesis in early amphibian development: histone and DNA syntheses are not co-ordinated. 1974, Pubmed, Xenbase