The retinal fate of Xenopus cleavage stage progenitors is dependent upon blastomere position and competence: studies of normal and regulated clones

Abstract

The clonal origin of the stage 43-44 Xenopus retina from cleavage stage precursors was quantitatively assessed with lineage tracing techniques. The retina descends from a specific subset of those blastomeres that form forebrain. The most animal dorsal midline cell (D1.1.1) produced about half of the retina, the three other dorsal ipsilateral blastomeres each produce about an eighth of the retina, and the four contralateral dorsal blastomeres and an ipsilateral ventral-animal cell together produce the remaining eighth of the retina. There was no significant spatial segregation of the clones derived from different progenitors in either the anterior-posterior or dorsal-ventral axes of the retina and no boundaries between clones were observed. Instead, the clones intermixed to form multiple radial subclones that were equivalent to those demonstrated by marking optic vesicle progenitor cells (Holt et al., 1988; Wetts and Fraser, 1988). This mosaic pattern was initiated by the beginning of gastrulation, advanced in the neural plate, and virtually complete in the optic vesicle. At optic vesicle stages cell movement within subclones was restricted, resulting in the formation of lineally related columns of cells in the mature retina. To determine if the blastomere progenitors are determined to produce these retinal lineage patterns, the major retinal progenitor (D1.1.1) was deleted bilaterally. About 60% of the tadpoles developed normal-appearing eyes; of these the retinas in two-thirds were normal in size and the rest were smaller. The blastomeres surrounding the deleted D1.1.1 progenitors changed their contributions to retina in different ways to effect a complete or partial restoration. Ventral blastomeres, which normally contribute mainly to the tail, produced substantial amounts of the retina while dorsal blastomeres, which normally contribute mainly to the head, decreased their contribution to the retina. To determine whether these changes in retinal lineage were due to changes in blastomere position after the surgery, various other blastomeres were deleted prior to lineage mapping. Dorsal-animal blastomeres took over the retinal fate of their dorsal-vegetal neighbors after those neighbors were deleted, but did not change fate after the deletion of their ventral-animal neighbors. This result suggests that dorsal-animal blastomeres change positional values in only one direction (dorsal to vegetal) after neighbor cell deletion, and that retinal fate is dictated by blastomere position. To test this hypothesis directly, different ventral and vegetal blastomeres, which normally do not produce retina, were transplanted to the position of D1.1.1.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Development of Direction Selectivity in Retinotectum by a Neural Circuit Model with Spike Timing-Dependent Plasticity

“…It has been reported that a retinal area is 0.09 mm 2 and the number of RGCs is 2700 per retina in Xenopus tadpole at stage 45 (Gaze and Grant, 1992). From this observation, we estimated the distance between nearest RGCs to be 6 m. On the other hand, we estimated the diameter of an RGC of Xenopus tadpole at stages 43-44 to be 11 m based on the anatomical study of Huang and Moody (1993). Therefore, we set the distance between 6 and 11 m. We confirmed that the development of direction selectivity by a fast-moving white bar (see below) can also be reproduced with the distance 10 ͌ 2 m, which is Ͼ11 m (data not shown).…”

Polycomb repressive complex PRC2 regulates Xenopus retina development downstream of Wnt/β-catenin signaling

“…Capped mRNAs were synthesized using Message Machine kit (Ambion). mRNAs for GFP (300 pg), β-galactosidase (β-gal; 200 pg) or Xenopus p15 Ink4b (1 ng; Open Biosystems) were injected in one dorsal animal blastomere at the eight-cell stage (Huang and Moody, 1993). Embryos were collected and staged according to Nieuwkoop and Faber (Nieuwkoop and Faber, 1967), and X-gal staining performed on β-gal-injected embryos as previously described (Turner and Weintraub, 1994).…”

“…Morpholinos against Ezh2 (ATG, 0.25 ng; UTR, 2.5 ng) or mRNA encoding ∆SET-Ezh2 (1 ng) were injected in one dorsal animal blastomere of 32-cell stage embryos along with 300 pg of GFP mRNA (Huang and Moody, 1993). GFP mRNA alone (300 pg) or control MO (0.5 ng) were injected as controls.…”

A directional Wnt/β-catenin-Sox2-proneural pathway regulates the transition from proliferation to differentiation in theXenopusretina

“…3D,E). We tested whether the promotion of Müller cells by Sox2 could also occur at Sox2 levels that could inhibit proneural activity, by injecting Sox2 mRNA into one dorsal animal blastomere at the 32-cell stage [targeting over 60% of the retina (Huang and Moody, 1993) We also wondered whether the increase in Müller cells caused by Sox2 overexpression could be due to a weak phenocopy of a constitutive Wnt/β-catenin signaling effect, in that extra Sox2 might maintain the progenitor fate for longer, so that when these Sox2-transfected cells eventually differentiate, they do so in a glialpromoting late environment. After continuous BrdU administration from stage 32 to 40, only 10% of control Müller cells were BrdU negative, i.e.…”