Genomic analysis of the mouse protamine 1, protamine 2, and transition protein 2 gene cluster reveals hypermethylation in expressing cells.
To understand the role of chromatin structure in the expression of the mouse protamine 1, protamine 2, and transition protein 2 genes during spermatogenesis, we have examined the genomic organization of this cluster of "haploid-specific" genes. As seen in the human genome, protamine 2, transition protein 2, and approximately 2.8 kb of a CpG island, hereafter called CpG island-dTP2, were clustered in a small region. Methylation analyses of this region have demonstrated that i) unlike most other tissue-specific genes, the protamine 1, protamine 2, and transition protein 2 genes were located in a large methylated domain in round spermatids, the cell type where they are transcribed, ii) the protamine 1 gene was only partially methylated in somatic cells and in testes from 7-day-old mice, and iii) the approximately 2 kb upstream and downstream of the CpG island-dTP2 were only partially methylated in somatic tissues. DNase I analysis revealed the presence of at least five strong DNase I hypersensitive sites over the CpG island-dTP2 in somatic tissues, but not in germ cells, and sequence analysis indicated that the CpG island-dTP2 is homologous to a CpG island located approximately 10.6 kb downstream of the human transition protein 2 gene. Although the nature of a CpG island-dTP2 and the function of a CpG island-dTP2-containing somatic tissue-specific DNase I hypersensitive sites in close proximity to the germ cell-specific gene cluster are unclear, the "open" chromatin structure of the CpG island-dTP2 may be responsible for the partial methylation pattern of the flanking sequences including the transition protein 2 gene in somatic tissues.
Choi
Y C
YC
Department of Biology, Tufts University, Medford, Massachusetts 02155, USA.
Aizawa
A
A
Hecht
N B
NB
D000818:Animals; D001483:Base Sequence; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics*; D003001:Cloning, Molecular; D018899:CpG Islands; D004247:DNA / Q000235:genetics; D019175:DNA Methylation; D015870:Gene Expression; D006238:Haploidy; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D015345:Oligonucleotide Probes / Q000235:genetics; D011479:Protamines / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D013091:Spermatogenesis / Q000235:genetics
D002868:Chromosomal Proteins, Non-Histone; D015345:Oligonucleotide Probes; C082073:PRM1 protein, human; C513176:Prm1 protein, mouse; D011479:Protamines; C068621:protamine 2; C053886:spermatid transition proteins; D004247:DNA