The @entity3308 ( @entity3308 ) of the vertebrate embryonic neural tube develops in response to the isthmic organizer (IsO), located at the midbrain-hindbrain boundary (MHB). @entity3308 derivatives are largely missing in mutants affected in IsO activity; however, the potentialities and fate of @entity3308 precursors in these conditions have not been directly determined. To follow the dynamics of @entity3308 maintenance in vivo, we used artificial chromosome transgenesis in @entity3392 to construct lines where egfp transcription is driven by the complete set of regulatory elements of @entity69995 , the first known gene expressed in the @entity3308 area. In these lines, egfp transcription faithfully recapitulates @entity69995 expression from its induction phase onwards. Using the stability of GFP protein as lineage tracer, we first demonstrate that @entity69995 expression at gastrulation is a selective marker of @entity3308 precursor fate. By comparing GFP protein and @entity69995 transcription, we further reveal the spatiotemporal dynamics of @entity69995 expression that conditions neurogenesis progression towards the MHB over time. Finally, we trace the molecular identity of GFP-positive cells in the acerebellar (ace) and no-isthmus (noi) mutant backgrounds to analyze directly @entity28628 and @entity69996 mutant gene activities for their ultimate effect on cell fate. We demonstrate that most @entity3308 precursors are maintained in both mutants but express abnormal identities, in a manner that strikingly differs between the ace and noi contexts. Our observations directly support a role for @entity28628 in protecting anterior tectal and metencephalic precursors from acquiring anterior identities, while @entity69996 controls the choice of @entity3308 identity as a whole. Together, our results suggest a model where an ordered @entity3308 pro-domain is identified at gastrulation, and where cell identity choices within this domain are subsequently differentially controlled by @entity28628 and @entity69996 functions.

Tracing of XXXX progeny in @entity3392 transgenics reveals the dynamics of midbrain-hindbrain neurogenesis and maintenance.

@entity69996 :: ('60636(Tax:7955)', 'Gene') :: ['Pax2.1', 'pax2.1'] @entity3308 :: ('MESH:D020295', 'Disease') :: ['midbrain-hindbrain domain', 'MH'] @entity28628 :: ('30538(Tax:7955)', 'Gene') :: ['Fgf8', 'fgf8'] @entity69995 :: ('30285(Tax:7955)', 'Gene') :: ['her5'] @entity3392 :: ('7955', 'Species') :: ['zebrafish']
@entity69995 :: (30285(Tax:7955),Gene) :: ['her5']
