8 research outputs found
Apoptosis and proliferation in the trigeminal placode
The neurogenic trigeminal placode develops from the crescent-shaped panplacodal primordium which delineates the neural plate anteriorly. We show that, in Tupaia belangeri, the trigeminal placode is represented by a field of focal ectodermal thickenings which over time changes positions from as far rostral as the level of the forebrain to as far caudal as opposite rhombomere 3. Delamination proceeds rostrocaudally from the ectoderm adjacent to the rostral midbrain, and contributes neurons to the trigeminal ganglion as well as to the ciliary ganglion/oculomotor complex. Proliferative events are centered on the field prior to the peak of delamination. They are preceded, paralleled and, finally, outnumbered by apoptotic events which proceed rostrocaudally from non-delaminating to delaminating parts of the field. Apoptosis persists upon regression of the placode, thereby exhibiting a massive “wedge” of apoptotic cells which includes the postulated position of the “ventrolateral postoptic placode” (Lee et al. in Dev Biol 263:176–190, 2003), merges with groups of lens-associated apoptotic cells, and disappears upon lens detachment. In conjunction with earlier work (Washausen et al. in Dev Biol 278:86–102, 2005) our findings suggest that apoptosis contributes repeatedly to the disintegration of the panplacodal primordium, to the elimination of subsets of premigratory placodal neuroblasts, and to the regression of placodes
Early development of the nervous system of the eutherian <i>Tupaia belangeri</i>
The longstanding debate on the taxonomic status of <i>Tupaia belangeri</i> (Tupaiidae, Scandentia,
Mammalia) has persisted in times of molecular biology and genetics. But way
beyond that <i>Tupaia belangeri</i> has turned out to be a valuable and widely accepted animal
model for studies in neurobiology, stress research, and virology, among
other topics. It is thus a privilege to have the opportunity to provide an
overview on selected aspects of neural development and neuroanatomy in
<i>Tupaia belangeri</i> on the occasion of this special issue dedicated to Hans-Jürg Kuhn.
Firstly, emphasis will be given to the optic system. We report rather
"unconventional" findings on the morphogenesis of photoreceptor cells, and
on the presence of capillary-contacting neurons in the tree shrew retina.
Thereafter, network formation among directionally selective retinal neurons
and optic chiasm development are discussed. We then address the main and
accessory olfactory systems, the terminal nerve, the pituitary gland, and the
cerebellum of <i>Tupaia belangeri</i>. Finally, we demonstrate how innovative 3-D reconstruction
techniques helped to decipher and interpret so-far-undescribed, strictly
spatiotemporally regulated waves of apoptosis and proliferation which pass
through the early developing forebrain and eyes, midbrain and hindbrain, and
through the panplacodal primordium which gives rise to all
ectodermal placodes. Based on examples, this paper additionally wants to
show how findings gained from the reported projects have influenced current
neuroembryological and, at least partly, medical research