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41.
42.
The ability of particular cell surface glycoproteins to recycle and become
exposed to individual Golgi enzymes has been demonstrated. This study was
designed to determine whether endocytic trafficking includes significant
reentry into the overall oligosaccharide processing pathway. The Lec1
mutant of Chinese hamster ovary (CHO) cells lack N -
acetylglucosaminyltransferase I (GlcNAc-TI) activity resulting in surface
expression of incompletely processed Man5GlcNAc2 N -linked
oligosaccharides. An oligosaccharide tracer was created by exoglycosylation
of cell surface glycoproteins with purified porcine GlcNAc-TI and
UDP-[3H]GlcNAc. Upon reculturing, all cell surface glycoproteins that
acquired [3H]GlcNAc were acted upon by intracellular mannosidase II, the
next enzyme in the Golgi processing pathway of complex N -linked
oligosaccharides (t1/2= 3-4 h). That all radiolabeled cell surface
glycoproteins were included in this endocytic pathway indicates a common
intracellular compartment into which endocytosed cell surface glycoproteins
return. Significantly, no evidence was found for continued oligosaccharide
processing consistent with transit through the latter cisternae of the
Golgi apparatus. These data indicate that, although recycling plasma
membrane glycoproteins can be reexposed to individual Golgi-derived
enzymes, significant reentry into the overall contiguous processing pathway
is not evident.
相似文献
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The histone demethylase, lysine (K)-specific demethylase 2A (Kdm2a), is highly conserved and expressed ubiquitously. Kdm2a can regulate cell proliferation and osteo/dentinogenic, adipogenic and chondrogenic differentiation of mesenchymal stem cells (MSCs) derived from dental tissue. We used quantitative real-time RT-PCR analysis and immunohistochemistry to detect Kdm2a expression during development of the murine molar at embryonic days E12, E14, E16 and E17 and postnatal days P3 and P14. Immunohistochemistry results showed no positive staining of Kdm2a at E12. At E14, Kdm2a was expressed weakly in the inner enamel epithelium, stellate reticulum cells and dental sac. At E16, Kdm2a was expressed mainly in the inner and outer enamel epithelium, stratum intermedium and dental sac, but weaker staining was found in cervical loop and dental papilla cells adjacent to the basement membrane. At E17, the strongest Kdm2a staining was detected in the ameloblasts and stronger Kdm2a staining also was detected in the stratum intermedium, outer enamel epithelium and dental papilla cells compared to the expression at E16. Postnatally, we found that Kdm2a was localized in secretory and mature ameloblasts and odontoblasts, and dentin was unstained. Real-time RT-PCR showed that Kdm2a mRNA levels in murine germ cells increased from E12 to E14 and from E14 to E16; no significant change occurred at E16, E17 or P3, then the levels decreased at P14 compared to P3. Kdm2a expression may be closely related to cell proliferation, to ameloblast and odontoblast differentiation and to the secretion of extracellular enamel and dentin during murine tooth development. 相似文献
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Technical comment on Boersma et al. (2016) Temperature driven changes in the diet preference of omnivorous copepods: no more meat when it's hot? Ecology Letters, 19, 45–53 下载免费PDF全文
Monika Winder Alfred Burian Michael R Landry David JS Montagnes Jens M. Nielsen 《Ecology letters》2016,19(11):1389-1391
A recent study concluded that omnivorous plankton will shift from predatory to herbivorous feeding with climate warming, as consumers require increased carbon:phosphorous in their food. Although this is an appealing hypothesis, we suggest the conclusion is unfounded, based on the data presented, which seem in places questionable and poorly interpreted. 相似文献
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In the current model for Glc3Man9GlcNAc2-P-P-Dol assembly, Man5GlcNAc2-
P-P-Dol, Man-P-Dol, and Glc-P-Dol are synthesized on the cytoplasmic face
of the ER and diffuse transversely to the lumenal leaflet where the
synthesis of the lipid-bound precursor oligosaccharide is completed. To
establish the topological sites of Glc-P-Dol synthesis and the
lipid-mediated glucosyltransfer reactions involved in
Glc3Man9GlcNAc2-P-P-Dol synthesis in ER vesicles from pig brain, the
trypsin-sensitivity of Glc-P-Dol synthase activity and the Glc-P-
Dol:Glc0-2Man9GlcNAc2-P-P-Dol glucosyltransferases (GlcTases) was examined
in sealed microsomal vesicles. Since ER vesicles from brain do not contain
glucose 6-phosphate (Glc 6-P) phosphatase activity, the latency of the
lumenally oriented, processing glucosidase I/II activities was used to
assess the intactness of the vesicle preparations. Comparative enzymatic
studies with sealed ER vesicles from brain and kidney, a tissue that
contains Glc 6-P phosphatase, demonstrate the reliability of using the
processing glucosidase activities as latency markers for topological
studies with microsomal vesicles from non-gluconeogenic tissues lacking Glc
6-P phosphatase. The results obtained from the trypsin-sensitivity assays
with sealed microsomal vesicles from brain are consistent with a
topological model in which Glc-P-Dol is synthesized on the cytoplasmic face
of the ER, and subsequently utilized by the three Glc-P-Dol-mediated
GlcTases after "flip-flopping" to the lumenal monolayer.
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50.