Electron Microscopic Radioautographic Study on Protein Synthesis in Mitochondria of Binucleate Hepatocytes of Aging Mice

Abstract

In order to study the aging changes of intramitochondrial protein synthesis in mouse hepatocytes, 10 groups of aging mice, each consisting of three individuals, total 30, from fetal day 19 to postnatal year 2, were injected with 3H-leucine, a protein precursor, sacrificed 1 h later, and the liver tissues processed for electron microscopic radioautography. On electron microscopic radioautograms obtained from each animal, the numbers of mitochondria, the numbers of labeled mitochondria, and the mitochondrial labeling index labeled with 3H-leucine that showed protein synthesis in each hepatocyte, both mononucleate and binucleate cells, were counted and the averages in respective aging groups were compared. From the results, it was demonstrated that the numbers of mitochondria, the numbers of labeled mitochondria, and the labeling indices of intramitochondrial protein syntheses in both mononucleate and binucleate hepatocytes of mice at various ages increased due to development of animals. The numbers of mitochondria, the numbers of labeled mitochondria, and the labeling indices of intramitochondrial protein synthesis in binucleate hepatocytes were more than those of mononucleate hepatocytes at the same aging stages.

Electron microscopic radioautographic study on mitochondrial RNA synthesis in adrenal cortical and medullary cells of aging mice

“…Thus, their results from the statistics obtained from the cytoplasmic grain counting seems to be not accurate without observing mitochondria directly. To the contrary, we had studied DNA synthesis in the livers of aging mice [16][17][18][19][20][21][22][23][24][25][26][27][28][29] and clearly demonstrated that the number of mitochondria in each hepatocytes, especially mononucleate hepatocytes, increased with the ages of animals from the perinatal stages to adult and senescent stages, while the number of labeled mitochondria and the labeling indices increased from the perinatal stages, reaching a maximum at postnatal day 14, then decreased. Our previous studies [22,23] also clarified that the DNA synthesis and cell proliferation by mitosis were the most active in the nuclei of mononucleate hepatocytes at the perinatal stages in contrast that binucleate cells were less active at the perinatal stage but the number of binucleate hepatocytes increased at senescent stages and the results suggest the possibility that the mitochondria in mononucleate hepatocytes synthesized their DNA by themselves which peaked at postnatal day 14 in accordance with the proliferation of mononucleate hepatocytes while binucleate hepatocytes increased after the perinatal stage and did not divide but remained binucleate keeping many mitochondria in their cytoplasm which were more in number than mononucleate hepatocytes at the senescent stage.…”

“…Thus, our previous papers [22][23][24][25][26][27][28] were the first that dealt with the relationship between the DNA synthesis and aging in hepatocytes of mice in vivo at various ages by means of electron microscopic radioautography observing the small dot-like silver grains, due to incorporations of 3 H-thymidine, which exactly localized inside the mitochondria. Our previous results [39][40][41][42] also revealed that an increase was observed by direct observation on mitochondria at electron microscopic level and obtaining accurate mitochondrial number and labeling indices in adreno-cortical cells in 8 groups of developing mice.…”

“…Intramitochondrial nucleic acid syntheses, both DNA and RNA, in mammalian and avian cells were first demonstrated morphologically by the present author by means of electron microscopic radioautography in primary cultured cells of the livers and kidneys of mice and chickens in vitro [1,2] and then in some other established cell lines such as HeLa cells [3][4][5][6] or mitochondrial fractions prepared from in vivo cells [7][8][9]. It was later commonly found in various cells and tissues not only in vitro obtained from various organs in vivo [10][11][12][13][14], but also in vivo cells of various organs such as the salivary glands [15], the liver [16][17][18][19][20][21][22][23][24][25][26][27][28][29], the pancreas [30,31], the trachea [32], the lung [33], the kidneys [34], the testis [35,36], the uterus [37,38], the adrenals [39][40][41][42], the brains [43], and the retina [44]…”

Electron Microscopic Radioautographic Study on Mitochondrial DNA Synthesis in Adrenal Cortical Cells of Developing and Aging Mice

“…Intramitochondrial nucleic acid syntheses, both DNA and RNA, in mammalian and avian cells were first demonstrated morphologically by the present author by means of electron microscopic (EM) radioautography, with accurate localization in primary cultured cells of the livers and kidneys of mice and chickens in vitro [1,2] and then in some other established cell lines, such as HeLa cells [3,4,5,6] or mitochondrial fractions prepared from in vivo cells [7,8,9]. They were later commonly found in various cells and tissues not only in vitro obtained from various organs in vivo [10,11,12,13,14], but also in vivo cells of various organs such as the salivary gland [15], liver [16,17,18,19,20,21,22,23,24,25,26,27,28,29], pancreas [30,31], trachea [32], lung [33], kidney [34], testis [35,36], uterus [37,38], adrenal gland [39,40,41], brain [42], and retina [43,44,…”

<b>Aging Changes of Macromolecular Synthesis in the Mitochondria of Mouse Hepatocytes as Revealed by Microscopic Radioautography</b>

“…3A) and 14 (Fig. 3B) to adult and senescent stages at postnatal month 1-24, were labeled (Nagata, 2006b(Nagata, , 2007c. The silver grains were also observed in binucleate hepatocytes at postnatal day 1 to month 1, 2 (Fig.…”