User:Philliskp/sandbox

hi

History
Through studies of human embryos performed in the late 1890s, Swiss anatomist Wilhelm His identified a portion of hindbrain neuroepithelium that was distinct from the rest of the hindbrain neuroepithelium in its morphology, sustained mitotic activity into late stages of embryogenesis, and deployment of streams of neurons through the hindbrain periphery. His named this zone "rautenlippe," or rhombic lip, because it appeared to emanate from the rhomboid-shaped opening of the fourth ventricle, much like the shape of a mouth. His proposed that the rhombic lip held the precerebellar precursors that would migrate ventrally to populate the pontine and olivary nuclei, but the methodologies available at the time limited the amount of evidence he could gather. The first real evidence that precerebellar neurons had a dorsal origin was obtained in the 1990s through the use of chick-quail chimeras, a technique in which portions of quail hindbrain neuroepithelium is grafted into chick embryos in ovo. Tracking the ventral migration of the quail daughter cells confirmed His' theory.

Rhombic Lip Development
Located between the fourth ventricle and the roofplate, the rhombic lip extends from r1-r8 and can be divided into upper, or cerebellar, and lower, or hindbrain, portions as the brainstem bends during later development. Expression of Math1, a transcription factor with a basic helix-loop-helix structure, governs the germinal epithelium of the rhombic lip and is expressed in midbrain and hindbrain regions as early as embryonic day 9.5 (E9.5). Math 1-null mice have been shown to lack several rhombic lip derivatives, including the granule neurons of the cerebellum and the pontine nucleus of the precerebellar system. The rhombic lip is organized according to a temporal fate map in which Math1-expressing precursors that first emigrate from the germinative layer (prior to E12.5) become deep nuclear neurons, while those exiting later (E13) become granule cells. Chick-quail chimera experiments have shown that r1 is the most likely source of granule cell precursors. Inside the rhombic lip, granule cell precursors divide and develop a unipolar morphology, with a single process that projects toward its destination.

dun http://www.ncbi.nlm.nih.gov/pubmed/11179876