Isolation of somatic cell glycoprotein mutants

Absence of CD9 reduces endometrial VEGF secretion and impairs uterine repair after parturition

In mammals, uterine epithelium is remodeled cyclically throughout adult life for pregnancy. Despite the expression of CD9 in the uterine epithelium, its role in maternal reproduction is unclear. Here, we addressed this issue by examining uterine secretions collected from patients undergoing fertility treatment and fertilization-competent Cd9^−/− mice expressing CD9-GFP in their eggs (Cd9^−/−TG). CD9 in uterine secretions was observed as extracellular matrix-like feature, and its amount of the secretions associated with repeated pregnancy failures. We also found that the litter size of Cd9^−/−TG female mice was significantly reduced after their first birth. Severely delayed re-epithelialization of the endometrium was then occurred. Concomitantly, vascular endothelial growth factor (VEGF) was remarkably reduced in the uterine secretions of Cd9^−/−TG female mice. These results provide the first evidence that CD9-mediated VEGF secretion plays a role in re-epithelialization of the uterus.

Sulfate suicide selection of Dictyostelium discoideum mutants defective in protein glycosylation

The assembly and processing of glycoprotein-linked oligosaccharides in Dictyostelium discoideum has been shown to generate a wide array of glycan structures which undergo dramatic developmental regulation. As late steps in processing of these oligosaccharides involve sulfation, a sulfate suicide selection procedure was developed to select for temperature-sensitive glycoprotein-processing mutants. Of 673 clones derived from the survivors of suicide selection, 99 were classified by replica-plating fluorography as temperature sensitive for sulfate transport or incorporation. Of these, 74 were unable to complete the developmental program to the fruiting body stage at the restrictive temperature, 29 being blocked in some aspect of aggregation and 45 being blocked at some postaggregation stage. Quantitative metabolic labeling experiments with representative clones showed that they incorporated wild-type levels of [35S]methionine but reduced levels of sulfate at the restrictive temperature. The specific incorporation patterns in the mutants suggest that distinct oligosaccharide-processing steps are involved in different developmental events.

Sulfate suicide selection of Dictyostelium discoideum mutants defective in protein glycosylation

The assembly and processing of glycoprotein-linked oligosaccharides in Dictyostelium discoideum has been shown to generate a wide array of glycan structures which undergo dramatic developmental regulation. As late steps in processing of these oligosaccharides involve sulfation, a sulfate suicide selection procedure was developed to select for temperature-sensitive glycoprotein-processing mutants. Of 673 clones derived from the survivors of suicide selection, 99 were classified by replica-plating fluorography as temperature sensitive for sulfate transport or incorporation. Of these, 74 were unable to complete the developmental program to the fruiting body stage at the restrictive temperature, 29 being blocked in some aspect of aggregation and 45 being blocked at some postaggregation stage. Quantitative metabolic labeling experiments with representative clones showed that they incorporated wild-type levels of [35S]methionine but reduced levels of sulfate at the restrictive temperature. The specific incorporation patterns in the mutants suggest that distinct oligosaccharide-processing steps are involved in different developmental events.

A novel type of Chinese hamster ovary cell mutant defective in oligosaccharide-lipid synthesis

A novel type of Chinese hamster ovary cell mutant has been isolated with a constitutive defect in the synthesis of lipid-linked oligosaccharides. This mutant, designated AS15-1, incorporates 30-fold less glucosamine into an oligosaccharide-lipid fraction than the wild type. A gel filtration analysis has shown that a small amount of oligosaccharide-lipid corresponding to Man5GlcNAc2-lipid is formed in the mutant. This mutant shows temperature sensitivity for both growth and adhesion to substratum, and constitutively secretes several unusual proteins in large amounts.

Lectin-resistant CHO cells: selection of new mutant phenotypes

Cytotoxic plant lectins select for mutants which exhibit unique structural changes in surface carbohydrates reflecting specific defects in glycosylation reactions. However, lectins are not highly specific selective agents and, as a result, only the most frequently occurring mutants are obtained from single lectin selections. We have previously shown that the specificity of lectin selections may be improved by utilizing a combination of lectins added together or sequentially. This strategy has now been further exploited in the search for novel lectin-resistant mutants of Chinese hamster ovary cells. Five new LecR phenotypes have been uncovered. One belongs to a new, recessive complementation group, two behave dominantly in somatic cell hybrids, and the remaining two appear to represent new phenotypes which fall into previously described complementation groups.