Prenatal differentiation of mouse vomeronasal neurones.

The vomeronasal organ (VNO) subserves basic chemosensory functions in rodents, mainly related to sexual behaviour. In order to understand early stages of the VNO structural maturation, we have undertaken an immunocytochemical analysis of the VNO of fetal mice. Our results demonstrate that Olfactory Marker Protein (OMP), a marker of differentiated chemosensory cells, is already expressed in vomeronasal neurones and their fibres projecting to the accessory olfactory bulb during the last week of gestation. However, in contrast to the adult, where its expression is restricted to the medial sensory neuronal component of the VNO, during fetal development OMP is also present in cells located in the lateral non-sensory epithelial component. Some other markers of nasal chemosensory neurones, such as GAP-43/B-50, Protein Gene Product 9.5 (PGP 9.5) and carnosine are also transiently expressed in this ectopic site. These results indicate that (i) significant morphological and biochemical maturation of the VNO is achieved before birth; (ii) transient cell populations, sharing the biochemical profile of the vomeronasal chemosensory receptors, occur in ectopic areas during fetal development.

GAP-43 and p75NGFR immunoreactivity in presynaptic cells following neuromuscular blockade by botulinum toxin in rat.

Peripheral nerve lesion results in changes in protein expression by neurons and denervated Schwann cells. In the present study we have addressed the question whether similar changes take place following functional denervation. Using immunohistochemistry and immunoelectron microscopy we examined changes in growth-associated protein (GAP-43) and low-affinity nerve growth factor receptor (p75NGFR) in rat gastrocnemius muscle following botulinum toxin-induced paralysis. GAP-43 and p75NGFR were selected because they are not expressed by mature intact motor neurons or Schwann cells, but are expressed following nerve lesion in both motor neurons and denervated Schwann cells. In control muscle, GAP-43 and p75NGFR immunoreactivity was seen only in nerve fibres near blood vessels. Two weeks after toxin injection, GAP-43 immunoreactivity could be seen at the motor endplates and in axons. Intensity of staining increased with longer survival and reached a peak between 4 and 8 weeks post-injection. Ultrastructurally, GAP-43 immunoreactivity was confined to nerve terminals and axons, whereas Schwann cells remained negative. Immunostaining for p75NGFR also increased following toxin injection and was detected in some terminal Schwann cells and in perineurial cells of small nerve fascicles near the paralyzed target cells, but not in axons. These results show that changes in expression of GAP-43 in motor neurons following functional denervation closely resemble the changes following anatomical interruption of nerve-muscle contact. GAP-43 was not expressed in Schwann cells, indicating that its upregulation in these cells is induced by loss of axonal contact or nerve degeneration products. There is no support for a role of p75NGFR in incorporation of neurotrophins in axons. The restriction of p75NGFR expression to terminal Schwann cells and perineurial cells in close proximity to the paralyzed target suggests a role for a target-derived signal or, alternatively, macrophages in eliciting this expression.

Resistance of metastatic tumor variants to tumor-specific cytotoxic T-lymphocytes not due to defects in expression of restricting major histocompatibility complex molecules in murine cells.

Metastases of ESb lymphoma cells in syngeneic DBA/2 animals frequently are selectively immunoresistant to lysis by syngeneic cytotoxic T-lymphocytes (CTL). This immunoresistance of tumor cells to CTL lysis could be due to a defect in either of two structures: (a) tumor-associated transplantation antigens; or (b) mouse major histocompatibility complex (H-2) antigens serving as restricting elements. In this study, we have analyzed the possible involvement of major histocompatibility complex Class I antigens in the immunoresistance of ESb tumor variant cells. Syngeneic anti-ESb CTL appeared to be H-2Kd restricted since only antibodies to Kd but not D,Ld molecules could inhibit CTL lysis. Comparison of H-2 antigens expressed on immunosensitive and resistant ESb sublines by immunofluorescence and flow cytofluorography, alloreactive CTL, two-dimensional gel analysis did not reveal any differences either qualitatively or quantitatively. Southern blotting of tumor-derived DNA with H-2-specific probes did not reveal differences either. Serologically detectable cell surface differentiation antigens were expressed very similarly on immunosensitive and resistant tumor lines, and only minor differences were noted by biochemical analysis of plasma membrane proteins. C-Type viral Mr 70,000 glycoprotein antigens were also similar in both types of cells. We conclude that cell surface changes on immunoresistant ESb variant cells are very selective and involve only CTL-defined tumor-associated transplantation antigen determinants.