THE ANNEXINS - SPECIFIC MARKERS OF MIDLINE STRUCTURES AND SENSORY NEURONS IN THE DEVELOPING MURINE CENTRAL-NERVOUS-SYSTEM

The annexins are a family of cytoplasmic proteins that have been shown to have numerous actions within a cell. Recent evidence suggests that at least one of these proteins plays a role in the development of the central nervous system (CNS). The present study examines the temporal expression and spatial distribution of annexins I, II, IV, V, and VI during development and at maturity in the murine CNS by immunocytochem ical analysis. The results demonstrate that annexins I, II and IV exhi bit clear immunolabeling in the murine CNS with distinct patterns of t emporal and spatial expression. Annexin IV is the first annexin to be expressed on embryonic day (E) 9.5 while annexin I is the last to be e xpressed (E11.5). Annexins I, II and IV are found in the floor plate r egion, but to differing rostrocaudal extents. Annexin I has a very res tricted distribution, only present in the midline raphe of the brainst em. Annexin II is present in the spinal cord, brainstem and mesencepha lon. Annexin IV has the widest midline distribution, being observed in the floor and roof plates of the developing CNS. Additionally, antibo dies against annexin II and TV immunolabel most dorsal root and sensor y ganglion cells and their axons. During early postnatal development, immunolabeling with each antibody gradually disappears in many structu res, and only first order sensory neurons and their fibers are immunop ositive for annexins II and IV at weaning. Three functions of the anne xins are suggested by the present findings: (1) to help establish the midline structures of the floor and roof plates, (2) to help direct th e decussation of sensory fibers, and (3) to regulate some aspect of se nsory neuron processing, such as signal transduction. (C) 1995 Wiley-L iss, Inc.