The earliest invasion of macrophages into the developing brain and eye of the tree shrew Tupaia belangeri

Abstract

The earliest occurrence of macrophages was investigated in the brain and optic anlagen of the tree shrew Tupaia belangeri. Nineteen serially sectioned embryos, belonging to five phases of programmed neuroepithelial cell death previously found during optic cup formation, were used. Macrophages were identified by structural criteria and by labelling with the lectin Griffonia simplicifolia I-B(4). Macrophages, most probably derived from the yolk sac, are present in the perineural vessels of the phase 1 embryo (V-shaped optic evagination). Within this compartment, their number increases up to phase 4 (advanced invagination) and drops during phase 5. This first wave of macrophages is followed by a second one occurring within the perineural mesenchyme and within the neuroepithelium of the brain and eyes from phase 3 onwards. In the phase 4 embryos, a considerable rise in the number of intraventricular macrophages is noted. During phase 5 (far advanced invagination), marked vascularization of the brain starts, and a peak of macrophages is noted in the neuroepithelium and in the ventricular lumen of the brain. This spatiotemporal pattern suggests that, in Tupaia, the earliest macrophages are simultaneously shifted from perineural vessels into the neuroepithelial walls of the developing brain and, at earlier stages than previously described in other vertebrate species, of the eye anlagen.

The patterns of cell death and of macrophages in the developing forebrain of the tree shrew Tupaia belangeri

“…In Tupaia, the earliest macrophages simultaneously invade the walls of the developing brain and eyes during phase 3 (Knabe and Kuhn 1999). The initiation of the midline band of cell death in the forebrain (phases 1 and 2; Fig.…”

“…GSA I-B 4 stains macrophages during earlier developmental stages than commercially available antibodies ( Fig. 1B; for method and control procedures, see Knabe and Kuhn 1999).…”

“…From phase 3 (onset of invagination) onwards these macrophages invade the walls of the brain and eyes from the outer or pial surface (Knabe and Kuhn 1999). The existence of distinct maxima of cell death, represented by bands or foci (Knabe and Kuhn 1998;present results), provides favourable conditions to analyze the spatial and temporal distribution of intraepithelial macrophages and their relationships to the pattern of cell death in the forebrain of Tupaia.…”

Early development of the nervous system of the eutherian <i>Tupaia belangeri</i>

“…Thereafter, macrophages emigrate from the perineural vessels, invade the anlagen of the forebrain and eyes from their pial/external surfaces, transmigrate the neuroepithelial wall, and, finally, arrive in the developing brain ventricles (Fig. 13a-d, Knabe and Kuhn, 1999). …”

To what extent are the retinal capillaries ensheathed by Müller cells? A stereological study in the tree shrew Tupaia belangeri

“…In our previous study we used the Griffonia simplicifolia isolectin-B % (GSA I-B % ) to discriminate GSA I-B % -labelled microglial cells from vessel-contacting horizontal cells (Knabe & Ochs, 1999). In Tupaia, GSA I-B % labels the earliest embryonic brain macrophages (Knabe & Kuhn, 1999) and, in the adult, microglial cells in the nerve fibre layer and in the inner plexiform layer of the central retina (Knabe & Ochs, 1999). The present study demonstrates by transmission electron microscopy that, in 1 case out of all capillary sections studied from the 3 outermost retinal capillary layers of Tupaia, the perikaryon of a microglial cell focally contacted the basal lamina of a capillary located in the inner plexiform layer (capillary layer 3, Fig.…”