The Questions of Developmental Biology

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Fig 9.35 Since it can diffuse only a short distance, the Gurken protein reaches only those follicle cells closest to the oocyte nucleus. Mutations of the Gurken gene in the mother (and thus in the oocyte) cause the ventralization of both the embryo and its surrounding follicle cells. Mutations of this gene in the mother (and thus in the oocyte) cause the ventralization of both the embryo and its surrounding follicle cells. (If the mutation is in the follicle cells and not in the egg, the embryo is normal.) Fig 9.36
The Gurken signal is received by the follicle cells through a receptor encoded by the torpedo gene. Molecular analysis has now established that gurken encodes a homologue of the vertebrate epidermal growth factor (EGF), while torpedo encodes a homologue of the vertebrate EGF receptor (Price et al. 1989; Neuman-Silberberg and Schüpbach 1993). Maternal deficiency of torpedo causes the ventralization of the embryo. Moreover, the torpedo gene is active in the ovarian follicle cells, not in the embryo. This was discovered by making germ line/somatic chimeras. Schüpbach (1987) transplanted germ cell precursors from wild-type embryos to embryos whose mothers carried the torpedo mutation. Conversely, she transplanted the germ cells of the torpedo mutant embryos to the wild-type embryos (Figure 9.37). When mated to wild-type males, the wild-type eggs produced ventralized embryos when they developed within the torpedo mutant mothers' follicles. The torpedo mutant eggs were able to produce normal embryos if they developed within a wild-type ovary. Thus, unlike the gurken gene product, the wild-type torpedo gene is needed in the follicle cells, not in the egg itself. Signal from the follicle cells to the oocyte cytoplasm. The activated Torpedo receptor protein inhibits the expression of the pipe gene. As a result, the Pipe protein is made only in the ventral follicle cells (Sen et al. 1998). The Pipe protein (in some as yet unknown way) activates the Nudel protein, which is secreted to the cell membrane of the ventral embryonic cells. A few hours later in development, the activated Nudel protein initiates the activation of three serine proteases that are secreted by the embryo into the perivitelline fluid (see Figure 9.35C; Hong and Hashimoto 1995). These three serine proteases are the products of the gastrulation defective (gd), snake (snk), and easter (ea) genes. Like most extracellular proteases, they are secreted in an inactive form and become activated by peptide cleavage. It is thought that the activated Nudel protein first tethers and activates the Gastrulation defective protein. This protease cleaves the Snake protein. This cleavage activates the Snake protease, which in turn cleaves the Easter protein. This cleavage activates the Easter protein, which cleaves the Spätzle protein (Chasan et al. 1992; Hong and Hashimoto 1995). The cleaved Spätzle protein is now able to bind to its receptor in the oocyte cell membrane, the product of the Toll gene. Toll protein is a maternal product that is evenly distributed throughout the cell membrane of the egg (Hashimoto et al. 1988, 1991), but it becomes activated only by binding the Spätzle protein, which is produced only on the ventral side of the egg. Therefore, the Toll proteins on the ventral side of the egg are transducing a signal into the egg, while the Toll receptors on the dorsal side of the egg are not.
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PART 1. Principles of development i
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PART 2: Early embryonic development
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15. Lateral plate mesoderm and endo
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Hox Genes: Descent with Modificatio
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The question of growth. How do our
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Embryonic homologies One of the mos
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absent (Figure 1.16A). Over 7000 af
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Such growth, in which the shape is
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One way to search for the chemicals
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2 3 hours as adults, and they must
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for the following spring's breeding
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VADE MECUM Amphibian development. T
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The formation of a cap is a complex
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In Chlamydomonas, recognition occur
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organism with two distinct and inte
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Aggregation is initiated as each of
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The mathematics of such oscillation
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gonidia to undergo a modified patte
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Sponges develop in a manner so diff
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Embryology provides an endless asso
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Environmental sex determination Sex
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Protection of the egg by sunscreens
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The Developmental Mechanics of Cell
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Autonomous specification was first
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In postulating this model, Weismann
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Insofar as it contains a nucleus, e
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Other tissues may use the same grad
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will give rise to its particular or
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Sydney Brenner (quoted in Wilkins 1
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The results of their experiments we
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This observation led Steinberg to p
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into a single layer of cells (Takei
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6. In conditional specification, th
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3. Geneticists had to explain pheno
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These events are not the normal rou
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differentiated; each of them contai
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federal proscription of human cloni
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ecombinase enzymes are active only
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In situ hybridization But where was
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damaged.) The second primer is adde
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By using the appropriate restrictio
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These homozygous mutant mice lacked
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Phenotype Manipulation This technol
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The second approach is candidate ge
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developmental genetics is different
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This gene consists of the following
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In addition to these basal transcri
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Enhancers are critical in the regul
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The third functional region of MITF
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A fourth enhancer sequence, located
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The discovery of the human globin L
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The results of this procedure are o
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In vertebrates, the presence of met
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chromatin that remains condensed th
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Second, knocking out one Xist locus
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types of cells (Kleene and Humphrey
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(Sxl) gene,* while the autosomes pr
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Table 5.3. Some mRNAs stored in ooc
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determine the anterior-posterior ax
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6. Cell-cell communication in devel
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The inducing tissue does not need i
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Instructive and permissive interact
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mouth, whereas the frog tadpole pro
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are utilized throughout the animal
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includes the TGF-β family, the act
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The RTK spans the cell membrane, an
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members of this family: the C. eleg
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The Wnt pathway Members of the Wnt
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The Hedgehog pathway is extremely i
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A series of mutations has been foun
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The Nature of Human Syndromes As we
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vertebral column deformities, myopi
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The mammalian homologue of CED-4 is
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In the absence of Notch gene transc
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extracellular matrix (Figure 6.32).
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mammary gland tissue. The binding o
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In some cells, gene transcription r
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PARTE 2. Early embryonic developmen
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The means by which sperm are propel
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The sperm released during ejaculati
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Lying immediately beneath the plasm
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The mechanisms of chemotaxis differ
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Once the sea urchin sperm has penet
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Removal of these threonine- or seri
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undergo the acrosomal reaction with
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Gamete Fusion and the Prevention of
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The fast block to polyspermy. The f
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envelope to expand and become the f
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The calcium ions responsible for th
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Thus, the conversion of NAD + to NA
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eticulum (McPherson et al. 1992). T
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cAMP-dependent protein kinase activ
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These cells divide to form embryos
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(Figure 7.34; Elinson and Rowning 1
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6. In many species, eggs secrete di
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One consequence of this rapid cell
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Table 8.1. Karyokinesis and cytokin
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provides a classification of cleava
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This occurred at precisely the time
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These rapid and invariant cell clea
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The identities of the signaling mol
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Ingression of primary mesenchyme Fu
Page 205 and 206: But these guidance cues cannot be s
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Page 209 and 210: The orientation of the cleavage pla
Page 211 and 212: stage, the remaining cells divide n
Page 213 and 214: embryos can produce these cells, bu
Page 215 and 216: Early Development in Tunicates Tuni
Page 217 and 218: (or inactivating) specific genes. T
Page 219 and 220: occur under laboratory conditions.
Page 221 and 222: the germ cells. Using fluorescent a
Page 223 and 224: Conditional specification As we saw
Page 225 and 226: eggs. Coda This chapter has describ
Page 227 and 228: 9. The genetics of axis specificati
Page 229 and 230: Following cycle 13, the oocyte plas
Page 231 and 232: Thus, at the end of germ band forma
Page 233 and 234: Classic embryological experiments d
Page 235 and 236: posterior region of the unfertilize
Page 237 and 238: Further studies have strengthened t
Page 239 and 240: The Hunchback protein also works wi
Page 241 and 242: transcription factor to activate an
Page 243 and 244: The gap genes The gap genes were or
Page 245 and 246: Table 9.2. Major genes affecting se
Page 247 and 248: The development of the normal patte
Page 249 and 250: However, the mechanism by which the
Page 251 and 252: As we saw above, the gap gene and p
Page 253 and 254: can substitute for Ultrabithorax an
Page 255: The Translocation of Dorsal Protein
Page 259 and 260: This fate map is generated by the g
Page 261 and 262: first glimpses of the multiple leve
Page 263 and 264: 10. Early development and axis form
Page 265 and 266: While these cells are dividing, num
Page 267 and 268: The next phase of gastrulation invo
Page 269 and 270: Black and Gerhart (1985, 1986) let
Page 271 and 272: The convergent extension of the dor
Page 273 and 274: During early gastrulation, three ro
Page 275 and 276: Spemann concluded from this experim
Page 277 and 278: Hans Spemann and Hilde Mangold: Pri
Page 279 and 280: We will take up each of these quest
Page 281 and 282: Moreover, the injection of exogenou
Page 283 and 284: These Nodal-related proteins will a
Page 285 and 286: The diffusible proteins of the orga
Page 287 and 288: Follistatin. The fourth organizer-s
Page 289 and 290: Frzb and Dickkopf. Shortly after th
Page 291 and 292: Moreover, when dorsal blastopore li
Page 293 and 294: The relationship between these thre
Page 295 and 296: Nodal protein activates expression
Page 297 and 298: 11. The early development of verteb
Page 299 and 300: Gastrulation in Fish Embryos The fi
Page 301 and 302: If one conceptually opens a Xenopus
Page 303 and 304: Left-right axis formation Little is
Page 305 and 306: thereby forming the secondary hypob
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This region, the germinal crescent,
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Axis Formation in the Chick Embryo
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The mechanisms for neural induction
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*Arendt and Nübler-Jung (1999) hav
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Compaction The fifth, and perhaps t
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Modifications for development withi
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The ectodermal precursors end up an
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These include the genes for transcr
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Experimental analysis of the hox co
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Kessel and Gruss (1991) found this
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Mice homozygous for an insertion mu
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7. In birds, gravity is critical in
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This tissue forms the amnionic sac
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12. The central nervous system and
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surrounding them. As much as 50% of
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Cell wedging is intimately linked t
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Fig 12.6 Human neural tube closure
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The anterior-posterior axis The ear
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Ventral patterning of the neural tu
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The time of this vertical division
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layer (Wallace 1999). Each Purkinje
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However, if these cells are transpl
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Neuronal Types The human brain cons
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Neurons transmit electrical impulse
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Development of the Vertebrate Eye A
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In addition, there are numerous Mü
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are shed and are replaced by new ce
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Just as there is a pluripotent neur
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13. Neural crest cells and axonal s
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The Trunk Neural Crest Migration pa
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Recognition of surrounding extracel
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However, D. J. Anderson's laborator
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Neural crest cells from rhombomeres
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the aortic arch arteries and the se
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Soon afterward, the expression patt
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Ericson and colleagues (1996) have
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That it must be a sort of a surface
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the G growth cone acts abnormally,
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Guidance by diffusible molecules Ne
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There is some reciprocity in scienc
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The activity of the synapse release
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Growth of the retinal ganglion axon
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The complicated nerve fiber circuit
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Snapshot Summary: Neural Crest Cell
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Fetal Neurons in Adult Hosts In 197
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Somites give rise to the cells that
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Eph signaling is thought to mediate
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(The dermis of other areas of the b
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Muscle cell fusion The myotome cell
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The mechanism of intramembranous os
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mitochondrial energy potential (Sha
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Mutations in FGFR1 can cause Pfeiff
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These buds eventually separate from
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Step 2: The metanephrogenic mesench
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Step 5: Conversion of the aggregate
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6. The two myotome regions are spec
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The Heart The circulatory system is
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This fusion occurs at about 29 hour
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Formation of Blood Vessels Although
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networks of each organ arise within
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In some instances, angiogenesis may
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This became apparent when experimen
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Blood and lymphocyte lineages. Figu
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Chick cells are readily distinguish
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In mammalian embryos, food and oxyg
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*In some infants, the septa fail to
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As Figure 15.27 shows, the stomach
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The surfactant enables the alveolar
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In mammals, the size of the allanto
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inhibits liver formation (Figure 15
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Moreover, as will be detailed in Ch
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These cells secrete the paracrine f
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Induction of the apical ectodermal
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The progress zone: The mesodermal c
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The mechanism by which Hox genes co
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Thus, while the Hox gene expression
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Charité and colleagues (1994) have
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Between the time when the cell's de
Page 463 and 464:
Snapshot Summary: The Tetrapod Limb
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This environmental view of sex dete
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The cells of the seminiferous tubul
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into the mesenchyme, but stay near
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There was a strict correlation betw
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Wnt4: a potential ovary-determining
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Anti-müllerian duct hormone Anti-M
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in another (see Jacklin 1981; Bleie
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Chromosomal Sex Determination in Dr
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The sex-lethal gene as the pivot fo
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Doublesex: The switch gene of sex d
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It is not known whether the tempera
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18. Metamorphosis, regeneration, an
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There are no ipsilateral (same-side
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Organ-specific response to thyroid
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The more T 3 receptors a tissue has
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Other species, such as A. tigrinum,
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Metamorphosis in Insects Types of i
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On one side of the sac, the epithel
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During the first larval instar, the
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central region producing the Wingle
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The molecular biology of hydroxyecd
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Since its discovery in 1954, when B
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How do they regain the ability to d
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It is probable that during normal r
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The head activator gradient. The ab
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*The tradition of leaving one's boo
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However, recent studies have indica
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Moreover, if a mutation occured in
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Snapshot Summary: Metamorphosis, Re
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19. The saga of the germ line We be
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In the nematode C. elegans, the ger
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When ultraviolet light is applied t
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Fibronectin is likely to be an impo
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Germ cell migration in birds and re
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EG Cells, ES Cells, and Teratocarci
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come together and are then separate
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The distal tip cell extends long fi
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The initiation of spermatogenesis d
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ecause the flagellum is beginning t
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A partial catalogue of the material
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When a specific 340-base sequence f
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Oocyte chromosomes can be incubated
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The structure of the meroistic ovar
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Periodically, a group of primordial
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Following ovulation, the luteal pha
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20. An overview of plant developmen
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oth the embryo and the mature sporo
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*A small weed in the mustard family
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should provide information on the e
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of hormones. In scarlet runner bean
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embryos demonstrate that isolated p
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When the shoot emerges from the soi
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etween nodes is called an internode
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flowering patterns among the over 3
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genes, class D genes are now being
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Table 21.1. Specific settlement sub
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Predictable Environmental Differenc
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Diapause Many species of insects ha
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The hindwing pigments of the short-
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Ferguson and Joanen (1982) speculat
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Predator-Induced Defenses One survi
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3. Antigens are presented (usually
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the ipsilateral eye. The situation
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*The importance of substrates for l
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Thus, most abnormal embryos are spo
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Retinoic acid as a teratogen In som
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Another pathway to apoptosis involv
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Whether heavy maternal alcohol cons
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Some scientists, however, say that
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Chains of causation Whether in law
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Snapshot Summary: The Environmental
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One could emphasize the common desc
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The search for the Urbilaterian anc
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Hox Genes: Descent with Modificatio
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Changes in Hox gene transcription p
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But within the crustacean lineages,
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Changes in Hox gene number The numb
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Homologous Pathways of Development
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The gradient of Dpp concentration f
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Modularity: The Prerequisite for Ev
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Such a trait would be selected for
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*The lack of such transitional form
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Coevolution of ligand and receptor
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Evidence for this mathematical mode
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It is difficult for a mutation to a
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The population genetics model conta
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However, once one adds development
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A partial list of genes active in h
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