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Cell Migration and Layer/Nuclear Formation

開催日 2014/9/11
時間 11:00 - 12:00
会場 Poster / Exhibition(Event Hall B)

Distinction between Reticular Tegmental Nucleus and Pontine Grey Nucleus ---- rhombomeric origin, Hox gene expression, and topographic organization

  • P1-089
  • 小林 正志 / Masashi Kobayashi:1 村上 富士夫 / Fujio Murakami:1 Zhu Yan / Yan Zhu:1 
  • 1:大阪大学大学院 生命機能研究科 / Graduate School of Frontier Biosciences, Osaka University 

The precerebellar rhombic lip (pRL) (encompassing rhombomere r6-r8) is a secondary germinal zone that gives rise to a number of hindbrain nuclei which send projections to the cerebellum. To understand how these different nuclei are constructed from a seemingly common progenitor zone has served an interesting model to reveal mechanisms underlying the formation of complex cytoarchitecture of mammalian brain.

Among the pRL-derived hindbrain nuclei, Reticular Tegmental Nucleus (RTN) and Pontine Grey Nucleus (PGN) comprise the large pontine nuclear complex (PN) positioned at ventral pons. The only criterion known to distinguish between the two nuclei is their final positions within PN, with RTN dorsal to, and PGN ventral to the longitudinally-traversing cortical spinal tract. Recently, it has been shown that PGN originate from r6-r8, and these neurons maintain the expression of Hox genes corresponding to their respective rhombomeric origin during and after their migration (Di Meglio et al, 2013). Furthermore, the relative rostrocaudal positions of their rhombomeric origin are topographically maintained during migration and faithfully translated to their rostrocaudal positions in the resulting PGN. However, whether RTN is constructed in a similar way is not known. Here in this study, we showed that RTN do not express Hoxb4 (r7/r8) and Hoxa5 (r8) raising the possibility that RTN may originate solely from r6.
We then employed focal in utero electroporation to target an EGFP construct into a small region of pRL in mice. We found that rostral pRL (r6) contribute extensively to RTN but caudal pRL do not, consistent with what has been inferred from the Hox gene expression. Interestingly, differing from the topography displayed in PGN, r6-derived RTN is not located above the r6-derived PGN but rather above the r7/r8 derived PGN, suggesting that these two closely related nuclei are constructed by distinct mechanisms. We will discuss the implication of our finding in the context of the potentially distinct behaviours between RTN and PGN neurons during the termination phase of their migration.

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