Zebrafish midbrain slow-amplifying progenitors exhibit high levels of transcripts for nucleotide and ribosome biogenesis

Abstract

Investigating neural stem cell (NSC) behaviour in vivo, which is a major area of research, requires NSC models to be developed. We carried out a multilevel characterisation of the zebrafish embryo peripheral midbrain layer (PML) and identified a unique vertebrate progenitor population. Located dorsally in the transparent embryo midbrain, these large slow-amplifying progenitors (SAPs) are accessible for long-term in vivo imaging. They form a neuroepithelial layer adjacent to the optic tectum, which has transitory fast-amplifying progenitors (FAPs) at its margin. The presence of these SAPs and FAPs in separate domains provided the opportunity to data mine the ZFIN expression pattern database for SAP markers, which are coexpressed in the retina. Most of them are involved in nucleotide synthesis, or encode nucleolar and ribosomal proteins. A mutant for the cad gene, which is strongly expressed in the PML, reveals severe midbrain defects with massive apoptosis and sustained proliferation. We discuss how fish midbrain and retina progenitors might derive from ancient sister cell types and have specific features that are not shared with other SAPs.

Embryonic origin and lineage hierarchies of the neural progenitor subtypes building the zebrafish adult midbrain

“…We therefore propose that the post-embryonic her5 -positive NE pool serves as a common source for the construction of the TeO, torus semicircularis and tegmentum, acting as a hub that orchestrates in time and space the construction of the midbrain. This appears similar to the function of the embryonic PML (Recher et al, 2013). Whether similar progenitor hierarchies are used in all domains remains to be demonstrated.…”

“…This demonstrated their contribution to the generation of neurons and oligodendrocytes populating the tegmentum, in the basal midbrain (Chapouton et al, 2006). In the embryo, the PML region also in part expresses her5 (Tallafuss and Bally-Cuif, 2003), and time-lapse imaging identified individual PML cells generating neurons in the PGZ, or in the TSc (Recher et al, 2013). Thus, the PML serves as a progenitor source for tectal and torus neurons in the embryo.…”

Mitotic cell rounding and epithelial thinning regulate lumen growth and shape

“…AB wild-type zebrafish strain, transgenic lines expressing Lifeact-GFP (Tg(actb1:lifeact-GFP)), Utrophin-GFP (Tg(actb1:GFP-utrCH)) 20 and Myosin light-chain GFP (Tg(b-actin:myl12.1-eGFP)) 20 , and the hi3820Tg ect2 mutant line 44,45 were maintained and bred according to the standard procedures 46 at the aquatic facility of Parc de Recerca Biomèdica de Barcelona (PRBB). All experiments conform to the guidelines from the European Community Directive and Spanish legislation for the experimental use of animals.…”

A Conserved Developmental Mechanism Builds Complex Visual Systems in Insects and Vertebrates

“…Similarly, dividing tectal progenitors become restricted to a peripheral hinge (tectal marginal zone; TMZ) between the optic tectum and torus semicircularis (Figure 3G–I). This hinge is formed when the torus semicircularis invaginates into the brain and comes to lie below the tectum, which occupies the dorsal and lateral parts of the brain [39] (Figure 3H,I). …”

“…This process includes several key features. Firstly, the external edge of the CMZ and TMZ (CMZe, TMZe) is formed by a ribbon of slowly dividing neuroepithelial stem cells [39,41,42] (Figure 4A,B) which accumulate transcripts for nucleotide and ribosome synthesis enzymes [39]. These genes form a synexpression group that provides a useful signature to compare neuroepithelial stem cells of the retina and tectum, as well as other stem cell types.…”