Expression data from 30do mouse spermatid [Affymetrix]

Chromatin performs numerous functions during cellular differentiation, and therefore it must be capable of adopting a multitude of different structures. How these various structures are established is poorly understood, but we propose that specific histone H2A variants will have a key role in remodelling chromatin during differentiation. Structurally, we show here that the gain of just a single acidic amino acid residue has generated a new mouse H2A.Bbd-like histone variant, H2A.Lap1, and that when incorporated into nucleosomal arrays imparts on them unique biophysical properties that are distinct from arrays containing either H2A or human H2A.Bbd. Functionally, we identify H2A.Lap1 as a novel chromatin component of active genes that are expressed during spermatogenesis, and in combination with H2A.Z create a unique chromatin landscape at the start site of transcription. During round spermatid differentiation, H2A.Lap1 dramatically loads onto the inactive X chromosome enabling a subset of its genes to be transcriptionally activated.

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Soboleva TA, Nekrasov M, Pahwa A, Williams R, Huttley GA, Tremethick DJ