Inhibitory control of neural differentiation in explants of Rana pipiens gastrula ectoderm
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Cited by 5 publications
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The influence of neural retina and lens on the development of embryonic lens vesicles in Amblystoma punctatum and Triturus viridescens
Embryonic lens vesicles from both species of salamander self-diff erentiated into a small lens with fibers when implanted into either the dorsal f i n or anterior chamber of the larval eye. Growth of these lenses was very slow in Amblystoma and somewhat faster in Triturus. When implanted into the pupil in place of the extirpated host lens, the embryonic lens vesicles differentiated normally and had a normal rate of growth. Lens regeneration from the host iris in Triturus was frequently inhibited by the implanted lens. A statistical analysis by the method of covariance showed that, in both species, lenses from the implants were largest in the lentectomized eyes, smaller in the vitreous chamber of eyes with intact host lens and smallest in the anterior chamber, host lens present. In Amblystma, the growth rates, as indicated by the coefficients for linear regression, were significantly different between lenses developing in the absence of the host lens and those growing from implants into either the anterior or vitreous chambers of eyes containing the host lens. In Trituru.~, a significant difference was observed only between growth rates of lenses in the lentectomized eyes and in the anterior chambers, host lens present or in the dorsal fin. These results show that the neural retina stimulates growth and differentiation of embryonic lens vesicles and that the host lens retards their growth.The regeneration of a lost part in an older animal frequently repeats many of the events of morphogenesis and cytodifferentiation that characterized the development of this structure during embryonic Iife. However, this takes place in an environment which is quite different from that found in an embryo. Unlike the embryonic anlage, the regenerating part is subject to local influences from adjacent differentiated tissues and to systemic influences such as hormones. The interactions of these factors have been extensively investigated in the many studies on regeneration of the amphibian limb. The regeneration of a lens from the pigmented epithelium of the dorsal iris in certain urodeles also repeats the events of morphogenesis and histogenesis observed in the embryonic development of the lens from the surface ectoderm overlying the optic vesicle and cup. In the embryo, lens development is stimulated and modu- namely, the entoderm of the dorsal-antenor archenteron wall, the adjacent mesoderm and, finally, the optic vesicle and cup (Liedke, '51, '55; Reyer, '58a, b; Jacobson, '55, '58, '63a, b, c). In the larval and adult eye, the presence of the neural retina is essential for the initiation of lens regeneration from the iris (reviewed by Stone, '59, '65; Goss, '64; Reyer, '54, '62a). This is normally released by extirpation of the host lens. It was of interest, therefore, to test the response of the prospective lens-forming ectoderm and embryonic lens vesicle to the environment of the differentiated eye, especially to any influences emanating from the host neural retina or lens. Experiments have already been reported (Reyer...
The influence of neural retina and lens on the development of embryonic lens vesicles in Amblystoma punctatum and Triturus viridescens
Embryonic lens vesicles from both species of salamander self-diff erentiated into a small lens with fibers when implanted into either the dorsal f i n or anterior chamber of the larval eye. Growth of these lenses was very slow in Amblystoma and somewhat faster in Triturus. When implanted into the pupil in place of the extirpated host lens, the embryonic lens vesicles differentiated normally and had a normal rate of growth. Lens regeneration from the host iris in Triturus was frequently inhibited by the implanted lens. A statistical analysis by the method of covariance showed that, in both species, lenses from the implants were largest in the lentectomized eyes, smaller in the vitreous chamber of eyes with intact host lens and smallest in the anterior chamber, host lens present. In Amblystma, the growth rates, as indicated by the coefficients for linear regression, were significantly different between lenses developing in the absence of the host lens and those growing from implants into either the anterior or vitreous chambers of eyes containing the host lens. In Trituru.~, a significant difference was observed only between growth rates of lenses in the lentectomized eyes and in the anterior chambers, host lens present or in the dorsal fin. These results show that the neural retina stimulates growth and differentiation of embryonic lens vesicles and that the host lens retards their growth.The regeneration of a lost part in an older animal frequently repeats many of the events of morphogenesis and cytodifferentiation that characterized the development of this structure during embryonic Iife. However, this takes place in an environment which is quite different from that found in an embryo. Unlike the embryonic anlage, the regenerating part is subject to local influences from adjacent differentiated tissues and to systemic influences such as hormones. The interactions of these factors have been extensively investigated in the many studies on regeneration of the amphibian limb. The regeneration of a lens from the pigmented epithelium of the dorsal iris in certain urodeles also repeats the events of morphogenesis and histogenesis observed in the embryonic development of the lens from the surface ectoderm overlying the optic vesicle and cup. In the embryo, lens development is stimulated and modu- namely, the entoderm of the dorsal-antenor archenteron wall, the adjacent mesoderm and, finally, the optic vesicle and cup (Liedke, '51, '55; Reyer, '58a, b; Jacobson, '55, '58, '63a, b, c). In the larval and adult eye, the presence of the neural retina is essential for the initiation of lens regeneration from the iris (reviewed by Stone, '59, '65; Goss, '64; Reyer, '54, '62a). This is normally released by extirpation of the host lens. It was of interest, therefore, to test the response of the prospective lens-forming ectoderm and embryonic lens vesicle to the environment of the differentiated eye, especially to any influences emanating from the host neural retina or lens. Experiments have already been reported (Reyer...
1. Recently the direct analysis of neural induction in the early chick embryo has become possible by the perfection of a technique for mechanical germ layer separation (HARA, 1961). This technique made it possible to interrupt the inductive process at various stages of development by separating the ectoderm from the inducing mesoderm anterior toHENSEN'S node. By subsequently culturing pieces of the isolated ectodermin vivo a study was made of the temporal sequence of appearance and the spatial extension of neural differentiation tendencies in the prospective neural ectoderm. 2. An area of the blastoderm anterior to the node was carefully freed of endo- and mesoderm with tungsten needles, and the remaining ectoderm was then cut into pieces of definite sizes with a glass needle. These pieces were culturedin vivo by means of transplantation into the coelome of 2 1/2 days old host embryos in order to assess their self-differentiation. 3. Donor blastoderms of four carefully defined stages (I-IV) were used: the nearly definitive and definitive streak stages, and the early and medium headprocess stages. The ectodermal area concerned was divided into a median zone and two lateral zones, and each of these zones was subdivided into two, three, or four anteroposterior areas, according to the stage used. The areas were designated with the letters 'A'-'D' for the median ones, and 'LA'-'LD' for the lateral ones. The 'A', 'LA', 'B', and 'LB' areas together always included the prospective prosencephalic region of the neurectoderm, whereas the remaining areas included the prospective mesencephalic region and part of the prospective rhombencephalic region (cf. Figs. 14, 16, 18, 20). 4. A total of 903 grafts prepared from 114 donor blastoderms were transplanted intracoelomically; 202 grafts were lost due to the death of the host embryos; out of the remaining 701 grafts 304 were recovered and studied histologically after 12 days of culturing. 5. There was a marked difference in the rates of recovery between grafts from the lateral and anteriormost median areas containing peripheral parts of the prospective neural anlage, and grafts from the more posterior median areas. The possible reasons for this difference were discussed. 6. The regional neural structures differentiating in the grafts were identified with the help of criteria established byHARA (1961) and extended in the course of the present study. 7. The results may be summarized as follows (cf. Figs. 14, 16, 18, 20): a. In all stages the relative numbers of grafts forming neural structures were lower in the lateral and anteriormost median graft areas than in the more posterior median areas. They generally increased from stage to stage in all graft areas, ranging from 0% in the anterolateral areas of stage I and II, to 100% in the posteromedian areas from stage III onwards. Among the lateral areas in any one stage it was always the area located at the level of the prechordal mesoderm (the 'LB' area) which showed the highest relative number of grafts forming neural structures. b...
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