The spatial and temporal pattern of C-Lmx1 expression in the neuroectodermduring chick neurulation

C-Lmx1 has been shown to be a key regulatory gene for specification of dors oventral pattern during vertebrate limb development. Here, we describe its earlier pattern of expression during and shortly after neurulation. Transcr ipts are first expressed in the mesoderm of the head process and rostral ti p of the primitive streak at the late gastrula/early neurula stage (stage 4 ). As neurulation occurs with shaping of the neural plate, C-Lmx1 is expres sed in a butterfly-like pattern in the lateral neuroectoderm. During bendin g of the neural plate, C-Lmx1 expression becomes localized to three areas o f the bending neuroectoderm the median hingepoint (future floor plate of th e neural tube) and the paired dorsolateral regions of the neuroepithelium, including the dorsolateral hingepoints and the adjacent neuroectodermal and epidermal ectodermal components of the neural folds. After closure of the neural groove and formation of the primary brain vesicles, C-Lmx1 is expres sed in the dorsal neural tube along the entire length of the neuraxis, as w ell as in the floor plate at the brain but not spinal cord levels. At the m idbrain and rostral hindbrain levels, C-Lmx1 is heavily expressed. Here, in addition to expression in the dorsal neural tube and floor plate, it is ex pressed in the lateral walls of the neural tube, with the exception of the levels of rhombomeres 2 and 4. C-Lmx1 is also expressed in several other di screte domains during and shortly after neurulation, including the prechord al plate and rostral head mesenchyme, foregut endoderm, otic placode and ve sicle, dorsal semitic mesoderm, midline endoderm at the level of the caudal spinal cord, mesonephroi and limb bud mesoderm. (C) 1999 Elsevier Science ireland Ltd. All rights reserved.