The development of mouse olfactory vesicles and their cell contacts: A freeze-etching study

Abstract

Cell membranes of adult mouse olfactory vesicles and cilia contain approximately 103/μm2 intramembranous particles (IMP) of 120 A in diameter. Sensory cilia are provided with a necklace of five to seven rows of IMP. Rosette-like IMP arrays in the otherwise randomly dispersed IMP in outgrowing and mature olfactory vesicles are thought to be their precursors. Both supporting and sensory cells are sealed by six to eight rows of tight junction strands. Their continuity was supported by observation of corresponding membrane fracture faces. Macular gap junctions in the cell apices and small gap junctions, located within the tight junctions, interconnect exclusively supporting cells. Their lumenal membranes are densely populated by large rodshaped IMP. In addition to the common globular IMP in lateral supporting cell membranes, a few rectangular clusters of 60 A IMP are scattered. Intraepithelial olfactory dendrites in fetal and young mice develop few discontinuous strands at their tips. The penetration process of the dendrites through the preexisting tight junction belt of supporting cells and vesicle formation involves fusion of tight junction strands, formation of a “complex” tight junction and finally reorganization of the strands to the mature pattern. The number of IMP in the presumptive vesicle region increases during outgrowth and reaches its final number in the mature vesicle.