Cystic fibrosis (CF) is caused by mutations in the CF transmembrane regulator (CFTR) that result in reduced anion conductance at the apical membrane of secretory epithelia. Treatment of CF patients carrying the G551D gating mutation with the potentiator VX-770 (ivacaftor) largely restores channel activity and has shown substantial clinical benefit. However, most CF patients carry the ΔF508 mutation, which impairs CFTR folding, processing, function, and stability. Studies in homozygous ΔF508 CF patients indicated little clinical benefit of monotherapy with the investigational corrector VX-809 (lumacaftor) or VX-770, whereas combination clinical trials show limited but significant improvements in lung function. We show that VX-770, as well as most other potentiators, reduces the correction efficacy of VX-809 and another investigational corrector, VX-661. To mimic the administration of VX-770 alone or in combination with VX-809, we examined its long-term effect in immortalized and primary human respiratory epithelia. VX-770 diminished the folding efficiency and the metabolic stability of ΔF508-CFTR at the endoplasmic reticulum (ER) and post-ER compartments, respectively, causing reduced cell surface ΔF508-CFTR density and function. VX-770–induced destabilization of ΔF508-CFTR was influenced by second-site suppressor mutations of the folding defect and was prevented by stabilization of the nucleotide-binding domain 1 (NBD1)–NBD2 interface. The reduced correction efficiency of ΔF508-CFTR, as well as of two other processing mutations in the presence of VX-770, suggests the need for further optimization of potentiators to maximize the clinical benefit of corrector-potentiator combination therapy in CF.

After labelling DNA with the specific vital fluorophore Hoechst 33342, oocytes, isolated by puncture from antral follicles in adult mice, have two essentially different configurations of their nuclear fluorescence images. These have been called SN (where the nucleolus is surrounded by chromatin) and NSN (where the nucleolus is not surrounded by chromatin). Intermediate configurations are also found, although with a lower frequency. The proportion of each class is on the average equal and depends neither on the presence of cumulus cells nor on the age of the mouse. Electron microscopy confirms several ultrastructural differences between these two nuclear configurations, namely, the structure of the nucleolus, which is vacuolated in NSN-type and compact in SN-type oocytes. Using video-enhanced fluorescence microscopy at low level of excitation light, we could follow directly in vitro the meiotic maturation of both classes, without impairing their viability. We show that in germinal vessicle (GV) state, the chromatin does not change from one configuration into the other and that both classes are able to mature to metaphase II, although the maturation has slightly different characteristics.

Eppig, 1977Eppig, , 1979Bachvarova et al., 1980

Reaction in R a t and Hamster Eggs 'DANIEL SLOLLOSI D q a r t m e n t of Riological Structure, Univrrsity of Wushington Seattle, Was king ton ABSTRACTThe origin of cortical granules is described in hamster and rat oocytes by electron microscopy. Thcy occur first near vesicular elements of small Golgi complexes. Most of these Golgi complexes lie peripherally, but in thc rat, there are a few also near the germinal vesicle. The granules arise at the concave surfaces of the Golgi cornplexcs and apparcntly migrate to the cell memhrane where they become aligned in close association to it. Cortical granules are found in the cytoplasm of the first polar body but not in the second. The cortical reaction, initiated by sperm attachment, consists of a gradual fusion of the membranes surrounding cortical granules with that of the egg plasma membrane and eversion of their contents into the perivitclline space, Occasionally, in the rat several granules fuse laterally to form larger cortical "caverns." Such caverns have a single opening to the perivitelline space. The origin and extrusion of cortical granules can be compared usefully with the synthesis and mcrocrine-type secretion of proteinaceous granules or mucoid droplets.