Gene Activity in Early Development (eBook)

Eric H. Davidson (Autor)

eBook Download: PDF | EPUB

2014 | 1. Auflage
388 Seiten
Elsevier Science (Verlag)
978-1-4832-6147-8 (ISBN)

Infos

Gene Activity in Early Development reviews the state of knowledge regarding genomic function in the programming and operation of what Bonnet, in 1762, described as 'the miracle of epigenesis.' The book is divided into four sections. Section I is concerned with gene activity in early embryogenesis, with the time of onset and the nature of embryo genome control, and with recent attempts to analyze the shifting patterns of gene expression as development proceeds. Section II reviews various classic and recent studies relevant to the phenomenon of cytoplasmic localization of morphogenetic potential and discusses the significance, from a contemporary vantage point, of this often neglected area of developmental biology. Section III deals with genomic function in oogenesis, beginning with a general survey of what could be described loosely as the natural history of the oocyte nucleus, and proceeding to current attempts to understand the character and the ultimate function of the oocyte gene products. Section IV discusses various aspects of the general problem of gene regulation in animal cells.

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Gene Activity in Early Development reviews the state of knowledge regarding genomic function in the programming and operation of what Bonnet, in 1762, described as "e;the miracle of epigenesis."e; The book is divided into four sections. Section I is concerned with gene activity in early embryogenesis, with the time of onset and the nature of embryo genome control, and with recent attempts to analyze the shifting patterns of gene expression as development proceeds. Section II reviews various classic and recent studies relevant to the phenomenon of cytoplasmic localization of morphogenetic potential and discusses the significance, from a contemporary vantage point, of this often neglected area of developmental biology. Section III deals with genomic function in oogenesis, beginning with a general survey of what could be described loosely as the natural history of the oocyte nucleus, and proceeding to current attempts to understand the character and the ultimate function of the oocyte gene products. Section IV discusses various aspects of the general problem of gene regulation in animal cells.

Inhalt

Front Cover 1
Gene Activity in Early Development 4
Copyright Page 5
Table of Contents 10
Dedication 6
Preface 8
Part I: gene actívíty ín early embryogenesís 14
Chapter 1. The varíable gene actívíty theory of cell dífferentíatíon 16
early evidence for the informational equivalence of differentiated cell genomes 16
altered cell fate experiments 17
DNA constancy and the reversibility of differentiation 18
failure to detect differences in the DNA sequences present in differentiated cells 20
direct evidence for the variable gene activity theory of differentiation 23
Chapter 2. The onset of genome control ín embryogenesís 25
the species hybrid experiments and their conceptual background 26
evidence for delayed onset of embryo genome control from echinoderm species-hybrid studies 30
embryo genome control in the development of species-hybrids in higher deuterostomes 34
interpretation of the species-hybrid experiments 36
development in physically enucleated embryos 37
"chemical enucleation" : development of actinomycin-treated embryos 39
the timing of transcription for early genome-controlled morphogenesis 43
Chapter 3. Early molecular índíces of dífferentíatíon 48
protein synthesis in actinomycin-treated sea urchin embryos 48
the appearance of histospecific proteins 51
Chapter 4. RNA synthesís ín the early embryo 55
informational and ribosomal RNA synthesis in early Xenopus embryos 55
the amount of the genome active in the early morphogenesis of Xenopus: RNA-DNA hybridization studies 66
change in the informational content of the newly synthesized embryo RNA's 72
informational and ribosomal RNA synthesis in the early sea urchin embryo 76
change in the patterns of transcription during early echinoderm development 80
patterns of early gene activity in other deuterostomes 83
pattern of early gene activity in protostomes 88
summary of biochemical data regarding onset of various classes of RNA synthesis in the embryogenesis of diverse animals 92
Chapter 5. The fate and functíon of early ínformatíonal RNA 95
evidence suggesting that early gene products serve as templates for early embryo proteins 95
evidence that early gene products are stored for later utilization 98
Chapter 6. Maternal template RNA 106
the demonstration of maternal template RNA 106
extraction of maternal template RNA and the nature of its program 108
fertilization and the activation of the maternal program 112
CONCLUSIONS 114
Part II: cytoplasmíc localízatíon and the onset of dífferentíatíon 116
Chapter 1. The localízatíon phenomenon 118
Chapter 2. Localízatíon and preformatíonísm 125
the origins of late-nineteenth-century "neopreformationism" 125
neopreformationism and development in lower protostomes 128
Chapter 3. Defínítíve experímental evídence for localízatíon 130
the capabilities of isolated blastomeres 130
blastomere specification as a consequence of factors present in the egg cytoplasm 135
cytoplasmic localization in the embryogenesis of Dentalium and Ilyanassa 140
Chapter 4. Regulatíve and mosaíc development, and the uníversalíty of morphogenetíc determínants ín egg cytoplasm 147
the orientation of cleavage and the mosaic vs regulative dichotomy 148
time of appearance of definitive cytoplasmic organization in various eggs 151
lability of localization patterns 156
localization, regulative development, and mosaic development 157
Chapter 5. Demonstratíons of localízatíon in regulatíve embryos 158
cytoplasmic determinants in the eggs of echinoderms 158
cytoplasmic localization in amphibian eggs 159
the universality of cytoplasmic localization 167
Chapter 6. Interpretatíons of the localízatíon phenomenon 168
the "embryo in the rough" 168
localization and cell differentiation 169
recent evidence for the selective gene activation theory of localization 171
CONCLUSIONS 177
Part III: Gene functíon ín oogenesís 178
Chapter 1. Origin and dífferentíatíon of the female germ líne 180
the origin of germ cells 180
general aspects of the timing of oogenesis in the chordate life cycle 183
oogenesis in sea urchins 192
panoistic and meroistic insect oogenesis 193
the occurrence of lampbrush chromosomes and the duration of the lampbrush stage 197
synopsis: temporal aspects of female germ-line differentiation 201
Chapter 2. Clues to oocyte genome functíon from organísms dísplayíng chromosome elímínatíon 203
Chapter 3. Accessory cell functíons ín oogenesís 206
the origin and physiological role of nurse cells 206
follicle cells 212
Chapter 4. Gene actívíty ín the oocyte nucleus: ríbosomal RNA synthesís 215
nucleolar function in the oocyte 215
the retention of ribosomal RNA synthesized in the amphibian oocyte 219
evidence that the free nucleoli of amphibian oocytes are the major sites of ribosomal RNA synthesis 221
nucleolar DNA and the selective replication of genes for ribosomal RNA 222
Chapter 5. Gene actívíty in the oocyte nucleus: synthesís of ínformatíonal RNA 230
the temporal location of informational RNA synthesis in oogenesis 230
lampbrush chromosome structure and DNA content 235
RNA synthesis in lampbrush chromosomes 239
the RNA and protein content of lampbrush chromosomes 241
informational RNA synthesis in the lampbrush-stage oocyte 242
the fate of lampbrush-synthesized informational RNA in later oogenesis 246
the fate of lampbrush-synthesized informational RNA in embryogenesis 248
the nature of the informational RNA inherited by the embryo 251
Chapter 6. 
257 
CONCLUSIONS 259
Part IV: ímmedíacy of gene control and the regulatíon of gene actívíty 260
Chapter 1. Very long-líved gene products 262
Chapter 2. Moderately long-líved ínformatíonal RNA 265
specific moderately long-lived template RNA's in the polysomes of differentiating tissues 265
a well-studied example: moderately long-lived template in hemoglobin-synthesizing cells 270
the presence of moderately long-lived template RNA and the repression of nuclear activity 273
moderately long-lived template RNA in microorganisms 277
Chapter 3. Rapídly decayíng template RNA 280
rapidly decaying template RNA in differentiated cells 282
the use of actinomycin in studies of template life 287
multiple levels of immediacy in gene control 289
significance of immediacy of gene control in the cellular genomic response system 291
changes of immediacy in embryonic development 292
Chapter 4. The rapídíty of varíatíons ín gene actívíty ín dífferentíated cells 295
Chapter 5. Characterístícs of bacteríal repressíon-derepressíon systems 299
the genetic basis for coordinate control and the generality of coordinate systems 300
polycistronic messenger RNA, the molecular basis of coordinate control 302
the operator gene concept 303
regulatory genes in coordinate and other systems 305
Chapter 6. Characterístícs of gene regulatíon systems ín dífferentíated cells 308
the proportion of the genome active in differentiated cells 308
relative change in gene function associated with change in state of differentiation 311
the nature of the repressive agents functioning in the differentiated cell genome 315
gene products of the differentiated cell nucleus 320
Chapter 7. Some hypotheses regardíng the nature of genomíc regulatíon ín dífferentíated cells 326
possible relevance of the operon concept 326
the nature of gene regulation in differentiated cells 328
conclusíon 337
Bíblíography 339
Author Index 370
Subject Index 381

Textauszug

2

The onset of genome control in embryogenesis

Publisher Summary

This chapter describes the onset of genome control in embryogenesis. The earliest stages of embryonic life also involve a certain amount of actual morphogenesis, in particular the construction of characteristic pregastrular structures, such as the hollow blastula of the echinoderm, or the structures demarcating the germinal layers from the nutrient syncytium in meroblastic eggs. Though specialized cellular structures, thus, exist even at these very early periods, pregastrular cells appear in general to be functionally nondifferentiated, at least in comparison to the situation following gastrulation when a variety of clearly specialized functional tissues has come into being. Differentiation in this discussion is defined as  [A2]

Wrong word copied the active manifestation of a specialized or histospecific cell function. This definition excludes functionally inactive cells, which are different from their neighbors merely by virtue of having passively inherited a different cytoplasm, or any cells that during a given period are carrying out no specialized function, irrespective of any possible synthesis of precursors for a future specialized function that might be taking place. The chapter reviews experiments that show in general that predifferentiation morphogenesis is independent of immediate control by the embryo cell genomes, while development from the onset of functional tissue level differentiation onward is directed by these same genomes.

It is now clearly established, at least for many deuterostome groups (echinoderms and lower chordates), that the initial, visible events of embryogenesis are not under the direct control of the embryonic cell genomes. These early events require active cell division, with all the complex biochemical processes thus entailed, including protein synthesis, membrane formation, mitotic spindle formation, chromosomal movements, DNA synthesis, etc. The earliest stages of embryonic life also involve a certain amount of actual morphogenesis, in particular the construction of characteristic pregastrular structures such as the hollow blastula of the echinoderm, or the structures demarcating the germinal layers from the nutrient syncytium in meroblastic eggs. Though specialized cellular structures thus exist even at these very early periods, pregastrular cells appear in general to be functionally nondifferentiated, at least in comparison to the situation following gastrulation when a variety of clearly specialized functional tissues has come into being. Differentiation in this discussion is defined as the active manifestation of a specialized or histospecific cell function. This definition excludes functionally inactive cells which are different from their neighbors merely by virtue of having passively inherited a different cytoplasm, or any cells which during a given period are carrying out no specialized function, irrespective of any possible synthesis of precursors for a future specialized function which might be taking place. The experiments we are now to review show in general that predifferentiation morphogenesis (which is to say, in lower deuterostomes, the major part of pregastrular morphogenesis) is independent of immediate control by the embryo cell genomes, while development from the onset of functional tissue level differentiation onward is directed by these same genomes. For the moment it is desirable to confine discussion to the submammalian deuterostomes, since by far the most is known about organisms belonging to this phylogenetic area, in particular sea urchins, ascidians, teleosts, and amphibians. The available data concerning protostomes and mammals in fact indicate that in both groups serious deviation from the echinoderm-amphibian pattern of events may exist.

the species hybrid experiments and their conceptual background

Effective investigation into the role of embryo genome control in morphogenesis can be said to have begun in 1889, with the first interspecific sea urchin hybrid experiments of Theodor Boveri (31), several earlier unsuccessful or inconclusive attempts notwithstanding. Boveri fertilized normal eggs and enucleate egg fragments of Spherechinus granulatus with sperm of a species belonging to a different genus, Echinus (= Parechinus = Psammechinus) microtuberculatus. The experiment was undertaken to determine if the nuclear substance alone is the bearer of hereditary qualities. Boveri reported that while true (diploid) hybrids between these species developed skeletal structures of a phenotypically hybrid character the (haploid) hybrid merogones formed by fertilizing enucleate eggs developed strictly in accordance with paternal type. These results, he believed, demonstrated the nuclear nature of the hereditary determinants, since the sperm contributes the only nuclear components in the hybrid merogone, and also emphasized explicitly the fact of embryo genome control over developmental morphogenesis and differentiation. This experiment was repeated in later years by Boveri himself, and in his last paper, which was published posthumously in 1918 (32), Boveri partially qualified his earlier results, pointing out several sources of error unknown in the 1890’s. Later workers, using far better methods, have learned much about hybrid sea urchin merogones that was not known in Boveri’s time. Some of the most important of these investigations have been carried out by Boveri’s former students such as Baltzer [see reviews in von Ubisch (33) and Hörstadius (34)]. If one takes into account the various artifacts and interpretative difficulties (33), Boveri’s early conclusions are in general correct, though real androgenetic haploid hybrids between the species originally used by Boveri do not in fact possess the range of developmental capacities he originally reported. In any case the Boveri experiment opened the way to an intensive experimental attack on the role of the embryo genome in early development by means of the species hybrid experiment. In these experiments hybrids are formed between species whose normal development differs sufficiently from the start so that by inspection it is possible to determine whether the course of development follows a maternal, a hybrid, or a paternal pattern. Since the genomic contents of the blastomere nuclei are replicas of the initial zygote fusion nucleus, observations of this nature could be expected to indicate the extent of genomic control over morphogenesis at each stage of development.

Both the technical and the conceptual developments which made these brilliant experiments possible had taken place only a very short time previously. Technically, the species hybrid experiments rested on the work of the Hertwigs, and it is interesting to note that it was during the period in which he was associated with the laboratory of R. Hertwig that Boveri carried out his first hybrid merogone studies. Only a few years earlier the Hertwigs had described the formation of normal and merogonal sea urchin hybrids; the conceptual background of the new line of investigation was almost as recent. At root in a theoretical (if not necessarily a historical) sense was the demonstration by Kölreuter, who, as early as 1761, showed that male and female parents contribute equally to the hereditary characters of the offspring (35). Kölreuter’s demonstrations apparently did not influence later workers in cellular embryology, and it was not until the writings of Nägeli in the 1880s that the attention of developmental biologists was drawn to this incisive early experimental study. By this time the conclusions Kölreuter had drawn were already assumed by many investigators; in the absence of the basic concept of equal parental contribution to inheritance it is of course impossible to understand the nature of pronuclear fusion and fertilization. Pronuclear fusion was apparently reported first by Warneke, who observed it in a snail egg in 1850, and by Bütschli (1873) who reported fusion in both nematode and snail eggs. Auerbach (1874) independently described pronuclear fusion in Ascaris, as did Hertwig and Fol in 1879 in the sea urchin [see Fol (36) for an extensive consideration of earlier and contemporary references]. Shortly thereafter Strasburger described pronuclear fusion in plants. These observations were of the utmost significance in that they produced the conviction that the nuclei of the male and female gametes are in fact the vehicle in which are borne the parental hereditary determinants.

Figure 3 (37) shows the pronuclei of a human egg as viewed in the electron microscope and also illustrates the apparent equality of the egg and sperm pronuclei, the very feature which was so suggestive to the early observers. The true significance of the pronuclear fusion phenomenon did not become completely clear until 1883, with the publication of Van Beneden’s careful observations of chromosomal movements before, during, and after fertilization in Ascaris.

FIGURE 3 Region of the penetrated human ovum with male and female pronuclei (PN). Nucleoli (n) and intrapronuclear annulate lamellae (ial) are in evidence. Note the numerous organelles which populate the cytoplasm adjacent to the pronuclei, (g) Golgi complex. ×5400. Zamboni, L., Mishell, D. R., Jr., Bell, J. H., and Baca, M., J. Cell Biol. 30, 579...

Produkt-Details

• Erscheint lt. Verlag: 28.6.2014
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Biologie ► Biochemie
• Themenwelt: Naturwissenschaften ► Biologie ► Evolution
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Angewandte Physik
• Themenwelt: Technik
• ISBN-10: 1-4832-6147-6 / 1483261476
• ISBN-13: 978-1-4832-6147-8 / 9781483261478