Developmental Processes in Higher Vertebrates Ruth Bellairs

Ellis, C. H.

doi:10.2307/1296326

Cited by 13 publications

(15 citation statements)

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“…Keibel (1906) provided figures, redrawn from published studies, of embryonic development in a wide range of vertebrates. However, with a few notable exceptions (Bellairs 1971) modern textbooks rarely consider species other than the common laboratory animals. There has been no textbook of descriptive comparative embryology in English, covering all the major vertebrate groups, for over 70 years (Jenkinson 1913;Kerr 1919).…”

Section: Introductionmentioning

confidence: 99%

There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development

Richardson

Howard

Gooneratne

et al. 1997

Anatomy and Embryology

275

148

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Embryos of different species of vertebrate share a common organisation and often look similar. Adult differences among species become more apparent through divergence at later stages. Some authors have suggested that members of most or all vertebrate clades pass through a virtually identical, conserved stage. This idea was promoted by Haeckel, and has recently been revived in the context of claims regarding the universality of developmental mechanisms. Thus embryonic resemblance at the tailbud stage has been linked with a conserved pattern of developmental gene expression - the zootype. Haeckel's drawings of the external morphology of various vertebrates remain the most comprehensive comparative data purporting to show a conserved stage. However, their accuracy has been questioned and only a narrow range of species was illustrated. In view of the current widespread interest in evolutionary developmental biology, and especially in the conservation of developmental mechanisms, re-examination of the extent of variation in vertebrate embryos is long overdue. We present here the first review of the external morphology of tailbud embryos, illustrated with original specimens from a wide range of vertebrate groups. We find that embryos at the tailbud stage - thought to correspond to a conserved stage - show variations in form due to allometry, heterochrony, and differences in body plan and somite number. These variations foreshadow important differences in adult body form. Contrary to recent claims that all vertebrate embryos pass through a stage when they are the same size, we find a greater than 10-fold variation in greatest length at the tailbud stage. Our survey seriously undermines the credibility of Haeckel's drawings, which depict not a conserved stage for vertebrates, but a stylised amniote embryo. In fact, the taxonomic level of greatest resemblance among vertebrate embryos is below the subphylum. The wide variation in morphology among vertebrate embryos is difficult to reconcile with the idea of a phyogenetically-conserved tailbud stage, and suggests that at least some developmental mechanisms are not highly constrained by the zootype. Our study also highlights the dangers of drawing general conclusions about vertebrate development from studies of gene expression in a small number of laboratory species.

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Section: Introductionmentioning

confidence: 99%

There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development

Richardson

Howard

Gooneratne

et al. 1997

Anatomy and Embryology

275

148

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“…Blood islands are condensations of splachnic mesoderm cells in close association with the underlying endoderm and are evident in the a. 0. v. at the head process stage (11,12,13). However, erythrocytes of the primitive and definitive lines are formed in the absence of gastrulation movements when the PS formation is inhibited mechanically (6,8).…”

Section: Discussionmentioning

confidence: 99%

Determination of Erythroid Cells in Unincubated Chick Blastoderm

Zagris

1985

Dev Growth Differ

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Portions the size of 1/6 to 1/32 part of unincubated blastoderm cultured in an albumen-salineagar solid medium form erythroid cells under conditions which suppress normal co-ordinated movements for mesoderm induction. Anterior and posterior regions of unincubated blastoderm have the same potentiality to form erythroid cells. The marginal zone seems to be the contributor of prospective erythroid cells. Portion 1/16 part of unincubated blastoderm forms morphologically distinct erythroid cells of the primitive and definitive lines as in normal development in ovo. It seems progenitor cell(s) is preprogrammed to a particular pattern of differentiation and/or includes differentiation to various erythroid cell types as an obligatory step. This system provides novel experimental possibilities in the study of erythroid cell determination and differentiation.The blastoderm of the newly laid chicken egg contains about 60,000 cells and consists of the 1 to 2-cell thick area pellucida and the thicker area opaca (1). The different regions of the pre-streak blastoderm are not completely equivalent to blood cell formation, but there is a definite region, more or less firmly commited to erythroid cell differentiation, which will give rise to the area opaca vasculosa (a. 0. v.) (2). However, this "determined" state can be shifted and multiple blood forming areas can be induced in the pre-streak blastoderm (3). It has been reported that stem cell(s), which give rise to primitive and definitive erythroid cell lines, arise in the yolk sac outside the embryonic body (4, 5, 6). Unincubated blastoderm in which the primitive streak (PS) and, consequently, the embryonic body are inhibited mechanically can form primitive and definitive erythrocytes and embryonic and adult hemoglobins (Hb) as in development in o w (6).In the work presented in this report, we determined the critical mass of portions from unincubated blastoderm capable of forming erythroid cells under conditions which suppress normal tissue associations and tissue interactions. In addition, we studied their capacity of forming erythroid cells characteristic of the primitive and definitive lines. These results give insights concerning the regulation of erythroid cell determination and differentiation in the early chick blastoderm. MATERIALS AND METHODS CultureFreshly laid White Leghorn chicken fertilized eggs were used. Unincubated blastoderms (stage X) (7) were removed from the yolk, washed free of the vitelline membrane and most of the adhering yolk, and carried in a drop of phosphate buffered saline solution (PBS-DULBECCO'S) with a widemouthed medicine dropper on SPRATT'S albumen-saline-agar (we substituted plain saline by PBS) solid medium.Blastoderms were stretched and dissected into 4, 8, 14, 16, 32 and smaller V (wedge) -shaped equal portions, their apices coincident with the center of the blastoderm, with fine dissecting steel needles. In some cases, portion 95

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“…It also allowed morphology and biochemistry to unite in addition to structure and function. The following texts, among others, may be considered representative of this period: Cellular Biology of E. de Robertis, The Epigenetics of Birds (Waddington, 1952) and Developmental Processes in Higher Vertebrates (Bellairs, 1971).…”

Section: Experimental Embryologymentioning

confidence: 99%

Evolution of embryology: A synthesis of classical, experimental, and molecular perspectives

Murillo-González

2001

Clin. Anat.

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Developmental Processes in Higher Vertebrates Ruth Bellairs

Cited by 13 publications

References 0 publications

There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development

There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development

Determination of Erythroid Cells in Unincubated Chick Blastoderm

Evolution of embryology: A synthesis of classical, experimental, and molecular perspectives

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