End plate classification and spontaneous sprouting in the sternocostalis muscle of the rat: A new whole mount preparation

Summary The sternocostalis muscle of the rat provides an ideal preparation for examination of neuromuscular junctions in a whole mount. It contains all three morphological end plate types (A, B and C), and its segmental innervation allows ease of experiment, such as partial denervation.The ratio of end plate types remains constant in all individuals of the same age, and there is no variation in this ratio over different regions of the same muscle. Spontaneous sprouting was observed from end plates of all the animals examined: again the ratio of sprouting end plate types remained constant over all muscles examined, and over all regions of the same muscle.     

Expression of the mouse PR domain protein Prdm8 in the developing central nervous system

It was first shown in the PR (PRDI-BF1 and RIZ homology) domain family proteins that the PR domain has homology to the SET (Su(var)3-9, Enhancer-of-zeste and Trithorax) domain, a catalytic domain of the histone lysine methyltransferases. Recently, there are many reports that the PR domain proteins have important roles in development and/or cell differentiation. In this report, we show the expression patterns of one of the mouse PR domain proteins, Prdm8, in the developing central nervous system. In the developing retina, Prdm8 expression was detected in postmitotic neurons in the inner nuclear layer and the ganglion cell layer, and its expression became restricted predominantly to the rod bipolar cells when retinogenesis was completed. In the developing spinal cord, Prdm8 was expressed first in the progenitor populations of ventral interneurons and motor neurons, and later in a subpopulation of interneurons. In the developing brain, Prdm8 expression was observed in postmitotic neurons in the intermediate zone and the cortical plate. In the postnatal brain, Prdm8 was expressed mainly in layer 4 neurons of the cerebral cortex. These results show that Prdm8 expression is tightly regulated in a spatio-temporal manner during neural development and mainly restricted to postmitotic neurons, except in the spinal cord.     

Mesodermal patterning during avian gastrulation and neurulation: Experimental induction of notochord from non-notochordal precursor cells

The cells that are normally fated to form notochord occupy a region at the rostral tip of the primitive streak at late gastrula/early neurula stages of avian and mammalian development. If these cells are surgically removed from avian embryos in culture, a notochord will nonetheless form in the majority of cases. The origin of this reconstituted notochord previously had not been investigated and was the objective of this study. Chick embryos at late gastrulal early neurula stages were cultured, and the rostral tip of the primitive streak including Hensen's node was removed and replaced with non-node cells from quail epiblast to ensure that the cells normally fated to be notochord would be absent and that healing of the blastoderm would occur. Embryos were allowed to develop for 24 hr, and the presence and origin (host or graft) of the notochord were assessed using antibodies against notochord or quail cells. Two notochords typically developed; both were almost exclusively of host origin. The primitive streak, and in some cases adjacent tissues, was removed from another group of embryos in an attempt to estimate the mediolateral position and extent of the cells required to form reconstituted notochord. Additional experimental embryos with and without grafts were transected at various rostrocaudal levels in an attempt to estimate the rostrocaudal extent of the cells required to form reconstituted notochord. Finally, various levels of the primitive streak either were placed in a neutral environment (the germ cell crescent) or were grafted in place of the node. Collective results from all experiments indicate that the areas lateral to the rostral portion of the primitive streak, estimated to have a rostrocaudal span of less than 500 μm and a mediolateral extent of less than 250 μm, are critical for formation of the reconstituted notochord. Fate mapping and histological examination of this region identify 4 possible precursor cell populations. Further studies are underway to determine which of the 4 possible precursor cell types forms or induces the reconstituted notochord, and which tissue interactions underlie this change in cell fate. © 1995 Wiley-Liss, Inc.