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Lens regeneration in Xenopus is not a mere repeat of lens development, with respect to crystallin gene expression.
Mizuno N
,
Mochii M
,
Takahashi TC
,
Eguchi G
,
Okada TS
.
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The spatio-temporal expression of three crystallin genes (alpha A, beta B1 and gamma) in lenses of Xenopus laevis was studied by in situ hybridization to compare the process of lens formation in embryonic development with that of lens regeneration from cornea that occurs in the tadpole. During embryonic lens development, all three crystallin transcripts were initially detected at the same stage of lens placode formation, and subsequently their signals became restricted to the presumptive lens fiber region. At later stages, the three crystallin genes were expressed in primary and secondary lens fibers, but not in lens epithelium. During lens regeneration, alpha A- and beta B1-crystallin signals were first detected in the presumptive lens fiber region of the lens vesicle. The expression of gamma-crystallin, however, appeared later than the other two crystallin genes and was detected only in morphologically discernible lens fibers. In the later stages of lens regeneration, expression of these crystallins was observed only in the lens fiber region, similar to embryonic lens development. These results reveal that lens regeneration from the inner layer of the outer cornea is not simply a repetition of embryonic lens development, when examined at the level of crystallin gene transcription.
Fig. 1A, B Nucleotide sequences of isolated cDNAs encoding
Xenopus crystallins. A αA-crystallin. B βB1-crystallin. The deduced
amino acid sequence is shown below the nucleotide sequence&/fi
Fig. 2A, B Deduced amino acid sequences of Xenopus crystallins
compared with sequences from other animals. A Amino acid sequences
of Xenopus Xα with αA-crystallins from Xenopus (partial
sequence), Rana catesbeiana, and rat. B Amino acid sequences of
Xenopus Xβ with βB1-crystallins from Xenopus (partial sequence),
chicken and cow. Asterisks represent conserved amino
acid residues. Sequences other than Xα and Xβ are derived from
the following references: Xenopus αA [8], Rana αA [20], rat αA
[4], Xenopus βB1 [1], chicken βB1 [15], cow βB1 [3]&
Fig. 3A–H In situ hybridization of sections through the eye region
of Xenopus embryo (A–D) and the regenerating lens (E–H)
hybridized with αA-crystallin probes. A Nieuwkoop-Faber stages
26–27. The inset panel is a high-magnification view of the lens
placode. Arrows indicate expression of αA-crystallin in the outer
layer of epidermis. B Nieuwkoop-Faber stages 28–29. C Nieuwkoop-Faber
stage 31. D Nieuwkoop-Faber stage 50. The inset
panel is a high-magnification view of lens tissue. E Freeman’s early
stage 3. F Freeman’s middle-to-late stage 3. G Freeman’s early
stage 4. H Freeman’s late stage 4; co cornea, di dorsal iris, lr iris,
l lens, le lens epithelium, lf lens fiber, lp lens placode, lv lens vesicle,
nr neural retina, oc optic cup, ov optic vesicle. The dorsal side
is up. Bar 100 μm. All panels except D are at the same magnification&/
Fig. 4A–H In situ hybridization of sections through the eye region
of Xenopus embryo (A–D) and the regenerating lens (E–G)
hybridized with βB1-crystallin probes. A Nieuwkoop-Faber stages
26–27. The inset panel is a high-magnification view of the lens
placode. Arrows indicate expression of βB1-crystallin in the outer
layer of epidermis. B Nieuwkoop-Faber stages 28–29. C Nieuwkoop-Faber
stage 31. D Nieuwkoop-Faber stage 50. The inset
panel is a high-magnification view of lens tissue. E Freeman’s early
stage 3. F Freeman’s middle-to-late stage 3. G Freeman’s early
stage 4. The H Freeman’s late stage 4. See legends to Fig. 3 for
abbreviations. The dorsal side is up. Bar 100 μm. All panels except
D are at the same magnification&
Fig. 5A–G In situ hybridization of sections through the eye region
of Xenopus embryo (A–D) and the regenerating lens (E–G)
hybridized with γ4-crystallin probes. A Nieuwkoop-Faber stages
26–27. The inset panel is a high magnification view of the lens
placode. Arrows indicate expression of γ-crystallin in the outer
layer of epidermis. B Nieuwkoop-Faber stages 28 to 29. C Nieuwkoop-Faber
stage 31. D Nieukoop-Faber stage 50. The inset
panel is a high magnification view of lens tissue. E Freeman’s
middle to late stage 3. F Freeman’s early stage 4. G Freeman’s
late stage 4. See legends to Fig. 3 for abbreviations. The dorsal
side is up. Bar 100 μm. All panels except D are at the same magnification&/fig
