Chromatin structure of the developmentally regulated early histone genes of the sea urchinStrongylocentrotus purpuratus

Abstract

Chromatin organization of the early histone gene repeat was studied at the early embryonic stages of the sea urchin S. purpuratus. Micrococcal nuclease digestion showed a highly irregular packaging of the whole repeat at the period of transcriptional activity, which was progressively replaced by more regular nucleosomal arrays upon developmentally programmed inactivation. No evidence for unique positioning of the nucleosomes was found. Regions upstream of each of the genes were hypersensitive to DNAase I digestion in the active state. These regions contained one (H2A and H2B), or two (H3 and H4) well-defined DNAase I cutting sites, or two poorly-defined sites (H1). They mapped within DNA sequences shown previously to be required for proper expression of the genes. Hypersensitivity continued in the hatching blastula, which have a conventional nucleosomal structure and a much reduced transcriptional activity. Hypersensitivity of these regions during morula and early blastula was not dependent on the torsional strain in chromatin, as it was not influenced by extensive gamma ray-induced nicking of the DNA in nuclei. By late blastula no hypersensitive regions were present.

Regulation of the Sea Urchin Early H2A Histone Gene Expression Depends on the Modulator Element and on Sequences Located near the 3′ End

“…Similarly, maximal and proper temporal expression of E-H1 gene depends on sequences that lie within the region -65 to + 39, including Inr and internal elements, while two other upstream binding sites have no apparent effect (Fei and Childs, 1993). In line with this assumption is the observation that a nuclease hypersensitive site that appears at the morula stage in the modulator sequence of both P. lividus and P. miliaris (Bryan et al, 1983;Anello et al, 1986), maps to a similar position in the active E-H2A gene of S. purpuratus (Fronk et al,1990). Unfortunately, sequence and functional data on the cis-acting sequences of S. purpuratus E-H2A promoter are lacking, so a direct comparison with our studies is not possible.…”

Down-regulation of Early Sea Urchin Histone H2A Gene Relies on cis Regulative Sequences Located in the 5′ and 3′ Regions and Including the Enhancer Blocker sns

“…In fact, during the period of maximum transcriptional activity, at early blastula stage, the chromatin of these genes does not present the regular nucleosomal package and is more accessible to digestion by endonucleases. Concurrent with transcription inactivation of a-histone genes at blastula stage, a defined regular micrococcal nuclease pattern reappears 22,[54][55][56] and two positioned nucleosomes probably assemble in the sns 5 fragment. 23,24 Transition from randomized to regular nucleosome spacing occurs also in the enhancer and TATA box-containing promoter region of the H2A gene (not shown).…”

Chromatin remodeling during sea urchin early development: molecular determinants for pronuclei formation and transcriptional activation

“…During sea urchin early development, transcriptional activation of the early histone genes correlates with changes in chromatin structure, along the promoter and coding sequences of these genes (Bryan et al, 1983;Wu and Simpson, 1985;Fronk et al, 1990;Jasinkas et al, 1998). Changes in nucleosome positioning and nuclease accessibility were detected in the proximity of transcriptional regulatory elements.…”

“…One site was found centered at À 60, in close proximity to the elements NFH3.1 and CCAAT. However, the transcription factors interacting with this region of the early histone H3 gene promoter have not been identified (Fronk et al, 1990). In the sea urchin Tetrapygus niger, it was found at DNase I hypersensitive domain centered at À 90 in the early histone H3 gene promoter which is only detected in embryos at the 128-cell stage expressing high levels of early histone H3 mRNA (Medina et al, 2001b).…”