Functional test of tight junctions in the mouse blastocyst

Abstract

THE mouse blastocyst contains a fluid-filled cavity, the blastocoele, which in normal Q-strain embryos first appears at about 83 h post coitum, when cleavage has produced a ball of about 30 cells¹. Two factors could be involved in the formation of the blastocoele: the secretion of fluid, which seems to be brought about by the coalescence and subsequent release of fluid-filled cytoplasmic vacuoles², and the development of tight intercellular junctions. Such junctions are first observed at the eight-cell stage, around the periphery of the embryo³; in the blastocyst they have increased in number and complexity to form the so-called ‘zonula occludens’, a permeability seal that can exclude lanthanum tracer from the blastocoele and thus presumably plays a role in maintaining the fluid turgor of the blastocyst⁴. By ‘immunosurgical’ dissection⁵ of Q embryos, we have investigated the stage of normal development at which the permeability seal becomes functional. We report here that impermeability to antiserum was not achieved until the mid-blastocyst stage (45–50 cells), and was not hastened or delayed by experimentally increasing or decreasing total cell number.