Activin A is expressed in endocrine precursor cells of the fetal pancreatic anlage. To determine the physiological significance of activins in the pancreas, a transgenic mouse line expressing the truncated type II activin receptor under the control of beta-actin promoter was developed. Histological analyses of the pancreas revealed that the pancreatic islets of the transgenic mouse were small in size and were located mainly along the pancreatic ducts. Immunoreactive insulin was detected in islets, some acinar cells, and in some epithelial cells in the duct. In addition, there were abnormal endocrine cells outside the islets. The shape and the size of the endocrine cells varied and some of them were larger than islets. These cells expressed immunoreactive insulin and glucagon. In the exocrine portion, there were morphologically abnormal exocrine cells, which did not form a typical acinar structure. The cells lacked spatial polarity characteristics of acinar cells but expressed immunoreactive amylase, which was distributed diffusely in the cytoplasm. Plasma glucose concentration was normal in the transgenic mouse before and after the administration of glucose. The insulin content of the pancreas in transgenic and normal mice was nearly identical. These results suggest that activins or related ligands regulate the differentiation of the pancreatic endocrine and exocrine cells.
Lipid droplets (LDs)
are closely related to lipid metabolism in
living cells and are highly associated with diverse diseases such
as fatty liver, diabetes, and cancer. Herein we describe a π-extended
fluorescent coumarin (PC6S) for visualizing LDs in living cells and
in the tissues of living mice using confocal fluorescence lifetime
imaging microscopy (FLIM). PC6S showed a large positive solvatochromic
shift and high fluorescence quantum yield (>0.80) in both nonpolar
and polar solvents. Additionally, the fluorescence lifetimes of PC6S
were largely dependent on solvent polarity. The excellent spectral
and photophysical properties of PC6S allowed its selective staining
of LDs in living and fixed cells, and multicolor imaging. Fluorescence
lifetime measurements of PC6S allowed estimation of the apparent polarity
of LDs. The high photostability and long intracellular retention of
PC6S supported in situ visualization of the formation processes of
LDs resulting from the accumulation of fatty acid. Furthermore, intravenous
administration of PC6S and use of the FLIM system allowed the imaging
of LDs in hepatocytes in living normal mice and the growth of LDs
resulting from the excess accumulation of lipids in high-fat-diet-fed
mice (fatty liver model mice). Taking advantage of the high selectivity
and sensitivity of PC6S for LDs in liver, we could visualize the adipocytes
of lipid-rich tissues and LDs in kidney peritubular cells by PC6S
fluorescence. These results demonstrated that PC6S combined with a
FLIM system can be useful for monitoring and tracking the formation
of LDs in both cultured cells and specific tissues and organs.
Phosphorescence lifetime imaging microscopy (PLIM) combined with an oxygen (O2)-sensitive luminescent probe allows for high-resolution O2 imaging of living tissues. Herein, we present phosphorescent Ir(III) complexes, (btp)2Ir(acac-DM) (Ir-1) and (btp-OH)3Ir (Ir-2), as useful O2 probes for PLIM measurement. These small-molecule probes were efficiently taken up into cultured cells and accumulated in specific organelles. Their excellent cell-permeable properties allowed for efficient staining of three-dimensional cell spheroids, and thereby phosphorescence lifetime measurements enabled the evaluation of the O2 level and distribution in spheroids, including the detection of alterations in O2 levels by metabolic stimulation with an effector. We took PLIM images of hepatic tissues of living mice by intravenously administrating these probes. The PLIM images clearly visualized the O2 gradient in hepatic lobules with cellular-level resolution, and the O2 levels were derived based on calibration using cultured cells; the phosphorescence lifetime of Ir-1 gave reasonable O2 levels, whereas Ir-2 exhibited much lower O2 levels. Intravenous administration of NH4Cl to mice caused the hepatic tissues to experience hypoxia, presumably due to O2 consumption to produce ATP required for ammonia detoxification, suggesting that the metabolism of the probe molecule might affect liver O2 levels.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.