Immunocytochemical localization of ZP3 in primordial follicles of rabbit, marmoset, rhesus monkey and human ovaries using antibodies against human ZP3.

Active immunization with zona pellucida (ZP) proteins leads to depletion of primordial and recruited follicles in the ovary by a yet unknown mechanism. Small amounts of ZP present on primordial follicles or granulosa cells may be one of the reasons for this ovarian pathology. This study was undertaken in an attempt to identify the presence of ZP in or on primordial follicles and granulosa cells in ovaries of rabbits, common marmosets (Callithrix jacchus), rhesus monkeys (Macacas mulatta) and humans. Therefore, monoclonal antibodies (mAbs) and rabbit and mouse antisera against recombinant human ZP3 (hZP3) were produced. All these antibodies bound to the ZP of native intact human oocytes. Several fixatives have been tested on pieces of rabbit ovaries. With 4% (w/v) paraformaldehyde in PBS (4% PFA) followed by paraffin embedding and cryostat sections postfixed with 4% PFA, the most intense staining of ZP with one of the mAbs was obtained and the morphology was well preserved. In humans, besides the ZP, the oocyte cytoplasm and granulosa cells of most primordial and recruited follicles were also stained with these antibodies. In rhesus monkey ovaries, all primordial oocytes were also stained, in addition to some granulosa cells of primary follicles. In marmosets, small dots of immunoreactive ZP were found on 60% of the primordial follicles but granulosa cells were not stained. In rabbits, only minor staining of primordial follicles was observed. After passive immunization of rabbits with mAb 4, antibodies were found on both primordial and recruited follicles. These results clearly show the presence of ZP3 on primordial follicles and in granulosa cells, and this could explain the ZP-induced ovarian pathology after active immunization with ZP3.

Melanocortin analogue Org2766 binds to rat Schwann cells, upregulates NGF low-affinity receptor p75, and releases neurotrophic activity.

Binding of the stable melanocortin(4-9) analogue, Org2766 [Met(O2)-Glu-His-Phe-D-Lys-Phe] to cultured rat sciatic nerve Schwann cells was demonstrated using a biotinylated derivative in semiquantitative histochemical and CELISA assays. Org2766 bound to Schwann cells, but not to fibroblasts, and was displaced maximally by unlabeled Org2766, alpha-MSH and ACTH(1-24). Displacement of Org2766 from the binding sites was considerably reduced by N- and C-truncation of the peptide. Specific binding of Org2766 was also demonstrated in the immortal rat Schwann cell line SCL4.1/F7 and was more pronounced in cells displaying a differentiated morphology. Org2766 and alpha-MSH increased cyclic AMP content of Schwann cells but neither stimulated DNA synthesis when applied alone. However, in the presence of a priming (subthreshold) concentration of the mitogen, cholera toxin, Org2766 and alpha-MSH caused a delayed increase in DNA synthesis. Org2766 did not modulate the expression of several differentiation-related Schwann cell markers. However, Org2766 increased immunoreactivity for p75 low-affinity NGF receptor on Schwann cells and evoked the release of neurotrophic factor(s) that synergized with NGF in stimulating neurite outgrowth in rat DRG neurons. The results indicate that Schwann cells are a primary target for the action of Org2766 and provide evidence for an indirect mechanism by which melanocortins might stimulate neurite sprouting in regenerating peripheral nerve axons.

Binding of a biotinylated neurotrophic ACTH(4-9) analogue, Org 2766, to neurofilament-positive cells in primary or cell line cultures.

To study the putative binding sites of the neurotrophic peptide Org 2766, an analogue of ACTH(4-9) [H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH], biotinylated forms of the peptide were used. After fixation, cultures of rat spinal cord and dorsal root ganglia were incubated with 4-10 microM of biotinyl-Org 2766 (b-Org 2766). Binding of both N- and C-terminally biotinylated Org 2766 was seen to phase-bright, round cells with thin processes, but not to flat, orthogonal-shaped cells with tapering processes. The b-Org 2766 binding was displaceable by an excess of nonbiotinylated Org 2766. Light and electron microscopy showed that the biotinylated peptide binds to a cytoplasmatic component as well as to the cell membrane. Double-labeling experiments with b-Org 2766 and an antibody (RT-97) to a high molecular weight neurofilament protein in dorsal root ganglion cultures showed, using fluorescence and confocal scanning laser microscopy, that all b-Org 2766 binding cells were neurofilament positive. Biotinylated Org 2766 did also bind to the neuronally differentiated cells in cultures of the human neuroblastoma cell line SK-N-SH, but not to those differentiated into epithelial cells. The present data suggest that the neurotrophic peptide Org 2766 binds specifically to cell types with neuronal characteristics.