Clarke H J, Bustin M, Oblin C
Department of Obstetrics and Gynecology, Royal Victoria Hospital, Montreal, Quebec, Canada.
J Cell Sci. 1997 Feb;110 ( Pt 4):477-87. doi: 10.1242/jcs.110.4.477.
We examined the distribution of the somatic subtypes of histone H1 and the variant subtype, H1(0), and their encoding mRNAs during oogenesis and early embryogenesis in the mouse. As detected using immunocytochemistry, somatic H1 was present in the nuclei of oocytes of 18-day embryos. Following birth, however, somatic H1 became less abundant in both growing and non-growing oocytes, beginning as early as 4 days of age in the growing oocytes, and was scarcely detectable by 19 days. Together with previous results, this defines a period of time when somatic H1 is depleted in oocytes, namely, from shortly after birth when the oocytes are at prophase I until the 4-cell stage following fertilization. At the stages when somatic H1 was undetectable, oocyte nuclei could be stained using an antibody raised against histone H1(0), which suggests that this may be a major linker histone in these cells. In contrast to the post-natal loss of somatic H1 protein, mRNAs encoding four (H1a, H1b, H1d, H1e) of the five somatic subtypes were present, as detected using RT-PCR in growing oocytes of 9-day pups, and all five subtypes including H1c were present in fully grown oocytes of adults. All five subtypes were also present in embryos, both before and after activation of the embryonic genome. mRNA encoding H1(0) was also detected in oocytes and early embryos. Whole-mount in situ hybridization using cloned H1c and H1e cDNAs revealed that the mRNAs were present in the cytoplasm of oocytes and 1-cell embryos, in contrast to the sea urchin early embryo where they are sequestered in the cell nucleus. We suggest that, as in many somatic cell types, the chromatin of mouse oocytes becomes depleted of somatic H1 and relatively enriched in histone H1(0) postnatally, and that somatic H1 is reassembled onto chromatin in cleavage-stage embryos. The post-natal loss of somatic H1 appears to be regulated post-transcriptionally by a mechanism not involving nuclear localization.
我们研究了组蛋白H1的体细胞亚型和变体亚型H1(0)及其编码mRNA在小鼠卵子发生和早期胚胎发育过程中的分布。通过免疫细胞化学检测发现，体细胞型H1存在于18天胚胎的卵母细胞核中。然而，出生后，无论是生长中的还是未生长的卵母细胞中，体细胞型H1的含量都逐渐减少，在生长中的卵母细胞中最早从4日龄开始减少，到19日龄时几乎检测不到。结合之前的研究结果，这确定了一个体细胞型H1在卵母细胞中被耗尽的时间段，即从出生后不久卵母细胞处于减数分裂前期I开始，直到受精后的4细胞阶段。在体细胞型H1无法检测到的阶段，卵母细胞核可以用针对组蛋白H1(0)产生的抗体进行染色，这表明H1(0)可能是这些细胞中的主要连接组蛋白。与出生后体细胞型H1蛋白的丢失相反，使用RT-PCR检测发现，在9日龄幼鼠生长中的卵母细胞中存在编码五种体细胞亚型中的四种（H1a、H1b、H1d、H1e）的mRNA，在成年小鼠完全成熟的卵母细胞中存在包括H1c在内的所有五种亚型。所有五种亚型在胚胎基因组激活前后的胚胎中也都存在。在卵母细胞和早期胚胎中也检测到了编码H1(0)的mRNA。使用克隆的H1c和H1e cDNA进行的全胚胎原位杂交显示，这些mRNA存在于卵母细胞和1细胞胚胎的细胞质中，这与海胆早期胚胎中它们被隔离在细胞核中不同。我们认为，与许多体细胞类型一样，小鼠卵母细胞的染色质在出生后体细胞型H1减少而组蛋白H1(0)相对富集，并且体细胞型H1在卵裂期胚胎中重新组装到染色质上。体细胞型H1出生后的丢失似乎是由一种不涉及核定位的机制在转录后进行调控的。
