Abstract
The chicken erythrocyte model system has been valuable to the study of chromatin structure and function, specifically for genes involved in oxygen transport and the innate immune response. Several seminal features of transcriptionally active chromatin were discovered in this system. Davie and colleagues capitalized on the unique features of the chicken erythrocyte to separate and isolate transcriptionally active chromatin and silenced chromatin, using a powerful native fractionation procedure. Histone modifications, histone variants, atypical nucleosomes (U-shaped nucleosomes) and other chromatin structural features (open chromatin) were identified in these studies. More recently, the transcriptionally active chromosomal domains in the chicken erythrocyte genome were mapped by combining this chromatin fractionation method with next-generation DNA and RNA sequencing. The landscape of histone modifications relative to chromatin structural features in the chicken erythrocyte genome was reported in detail, including the first ever mapping of histone H4 asymmetrically dimethylated at Arg 3 (H4R3me2a) and histone H3 symmetrically dimethylated at Arg 2 (H3R2me2s), which are products of protein arginine methyltransferases (PRMTs) 1 and 5, respectively. PRMT1 is important in the establishment and maintenance of chicken erythrocyte transcriptionally active chromatin.
Highlights
The chicken erythrocyte is a useful model system to study the organization and function of a vertebrate genome and to discover the salient features of transcriptionally active chromatin [1]
The landscape of histone modifications relative to chromatin structural features in the chicken erythrocyte genome was reported in detail, including the first ever mapping of histone H4 asymmetrically dimethylated at Arg 3 (H4R3me2a) and histone H3 symmetrically dimethylated at Arg 2 (H3R2me2s), which are products of protein arginine methyltransferases (PRMTs) 1 and
The following features of transcriptionally active chromatin were first documented in studies using chicken erythrocytes: (1) transcriptionally active chromatin is sensitive to DNase I digestion, showing that active chromatin has a “loosened” chromatin structure [3,4]; (2) the boundaries of transcriptionally active chromatin domains are defined by their DNase I sensitivity [5]; (3) the DNase I sensitivity of transcriptionally active chromatin is increased when the torsional stress of the transcriptionally active chromatin domain is maintained [6,7]; (4) direct demonstration that acetylated histones are associated with the DNase I sensitive transcriptionally active chromatin [8,9]
Summary
The chicken erythrocyte is a useful model system to study the organization and function of a vertebrate genome and to discover the salient features of transcriptionally active chromatin [1]. Many sources of chromatin have 0.8 to 1.0 H1 molecules per nucleosome (rat liver, chicken liver, glial nuclei from ox cerebral cortex, pig lymphocytes), Cells 2021, 10, 1354 of 13 than any other chromatin source [10]. H1/H5 from rendering the active gene chromatin insoluble at will discuss later, histone acetylation, which is limited to transcriptionally active chromatin, physiological ionic strength [11].the. This composition of the chicken chromatin prevents H1/H5 from rendering active gene chromatin insolubleerythrocyte at physiological ionic makes this source of chromatin highly suitable to a chromatin fractionation procedure, strength [11].
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