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本帖最后由 细胞海洋 于 2010-11-30 12:27 编辑
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Developmental Genetics, or What Can Genetics and Genomics Tell Us About Evolution, Development, Stem Cells, Human Birth Defects, and Disease?6 S8 l5 v6 j% i2 j6 g }' j3 M
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The ability of researchers to answer experimental questions greatly depends
. G$ |# ~7 f) ~$ j( R+ q H' non the available technologies. New technologies lead to novel observations
# N1 D# r6 O5 p' Z6 Qand field-changing discoveries and influence the types of questions that can
" C$ s. B K: z. Sbe asked. Today’s recently available technologies include sequencing and analyzing% t% I6 E5 I, J8 {4 j- \
the genomes of human and model organisms, genome-wide expression
) H/ [3 i b6 O0 {5 ?" `# Pprofiling, and high-throughput genomic and genetic analyses. The information7 [2 i! ~5 W% t: Y i; E, g2 L
provided by these approaches is enabling us to begin to understand the
; T( F5 c* _9 a- x/ ^* _complexity of many biological processes through the elucidation of gene regulatory
# b/ t3 G3 }( s, ~networks, signaling pathway networks, and epigenetic modifications.: ?+ h; ?) d: o
This book describes many lines of research that are being impacting by these
( Q3 y8 m! p; j8 J5 _new technologies, including developmental genetics and the related fields of; [. u. v. t& m
clinical genetics, birth defects research, stem cell biology, regenerative medicine,
" G5 |7 { E+ F; J4 eand evolutionary biology.
& K3 e# E, N1 r% Z# D' R7 ?4 UThe field of developmental genetics, or the study of how genes influence. L3 ^1 E$ i: W S9 a8 q% m
the developmental processes of an organism, has been influenced by new technologies
7 ~% X! k2 u+ i- L: c3 X8 band by interactions with other fields of study throughout its history.
9 K6 V2 L6 K* k0 TThe concept of a genetic basis of development began in “modern” times at the1 p4 p: p( @5 W/ L
intersection of descriptive embryology and cytology. Modern histological% J N' v7 E) x9 k7 P$ T5 D$ o5 V
techniques were developed in the mid-19th century, largely by Wilhelm His! j( p3 ?; J& T! B# t
so that he could study cell division in the neural tube, which enabled visualization4 P% c. k* q- X/ O9 |/ a
of the cell nucleus, chromosomes, and the discrete steps of mitosis.5 n* A4 ~8 D# Q8 ]8 O
Theodor Boveri cleverly applied these improved microscopic techniques to- Y. ~# |; G K) o. T6 D2 V% U
transparent marine embryos to demonstrate that each parent contributes& j4 d& `1 f6 I1 V9 a+ T
equivalent groups of chromosomes to the zygote, and that each chromosome
. s+ l8 m5 m8 p: uis an independently inherited unit. Importantly, he noted that if an embryo1 W2 I5 {2 b2 D( X. |0 L6 b' @
contains the incorrect number or improper combination of chromosomes, it# s9 P' K( r! A
develops abnormally.5 i$ M. C$ q" |
However, many early embryologists rejected the idea that development is
* w0 H ~/ a/ X$ R+ J7 K6 Idriven by prepackaged heritable particles because it seemed too similar to the8 j9 c: L3 ^5 N$ m( h8 C
idea of “preformation”: the concept that development is driven by predetermined
6 ~; I! l6 E$ bfactors or “forces” (sometimes described in rather mystical terms).& S! Q+ H3 o) C: X0 B9 X L9 I+ ~
Wilhelm Roux, an advocate of studying the embryo from a mechanistic point
' i: i0 r% R& k8 Y3 m1 ?% Oof view, was a leader in the approach of manipulating the embryo with microsurgical
8 C1 N9 H3 _- z1 Y/ }# ^+ Ctechniques to elucidate cause and effects between component parts, j- a. I, E+ {3 u! H' @$ N# N
(experimental embryology). By using an animal model whose embryos were
' w: i! X6 {, ~large, developed external to the mother, could be surgically manipulated with8 t! F H% ]+ m9 b6 [, [
sharpened forceps and cultured in simple salt media (i.e., amphibians), he0 B1 ^, R4 [/ P/ J/ k0 O
rejected the role of predetermined factors and demonstrated the importance( V1 `* a5 O: J9 [; M& q$ u
of external (epigenetic) influences and cell–cell interactions in regulating
5 r7 S# }$ ^# d) Rdevelopmental programs. Experimental embryologists further refined their) s& B' t c9 C
skills at dissecting small bits of tissue from the embryo, recombining them: Q0 Z2 \5 h6 K5 w4 f
with other tissues in culture or transplanting them to ectopic regions in the
. q2 P* N, L" E `; W2 Rembryo. This work led to the invention of tissue culture by Ross Harrison
( R& M `2 E$ v' b6 S: l; b' iand the discovery of tissue inductions by Hans Spemann.
+ Q$ V, }; l" I. y3 q# W1 p4 V- e, QWhile experimental embryology was thriving, T. H. Morgan founded the
7 S$ i0 O3 F) n" ^' c/ t# _) ~field of Drosophila genetics. Also trained as an embryologist, Morgan was, N2 A9 z2 h; m3 H/ n6 |
skeptical of Boveri’s idea of heritable packets, and directed his studies towards D E5 D5 Z; F7 E: U
understanding the principles of inheritance. For several decades, the two fields$ G* K# V8 a, ~6 E4 j
had little impact on one another. Interestingly, however, after a few decades of
8 _# `, A# V/ r# B9 pstudy of the fruit fly, Morgan’s work supported the idea of discrete intracellular
6 b" |# M5 V! Zparticles that directed heritable traits, which he named “genes.” Nonetheless,) y* d1 c9 |' V
the fields of experimental embryology and genetics remained fairly# G: U* Z3 I# x5 ~" A9 j
separate entities with distinct goals and points of view. Embryologists were
2 U& H% i9 ]8 b( ~1 {$ B+ l% ^2 Relucidating the interactions that are important for the development of numerous
# K1 e8 Y9 X# H* R3 J9 S4 ^tissues and organs, whereas geneticists were focused on the fundamentals
% t/ e! e0 w( t( Kof gene inheritance, regulation of expression, and discovering the genetic" D1 G8 Q4 D* S A6 S, \
code. Indeed, elucidating the genetic basis of vertebrate development was, f+ |$ b K7 j3 O1 B6 e& e
delayed until new technologies in molecular biology and cloning were devised.
: a8 Y+ g! V. y H3 KFrom the field of bacterial and viral genetics came the techniques for cloning
# Y2 W M+ E9 Heukaryotic genes and constructing vectors for controlling expression. From1 R: R0 `$ O+ k; J
the classical genetic studies in fly and nematode came the rationale for mutagenizing/ {3 O+ z* C' N5 I* R
the entire genome and screening for developmental abnormalities.* ~+ V* _2 V5 N- h$ _
Important regulatory genes were discovered in these invertebrates, and their# H8 C5 T6 ?+ L- |, ^" T
counterparts were discovered in many other animals by homology cloning: a8 v9 z/ k. T# P1 G+ v# q5 f" [
approaches. Thus was born the modern field that we call developmental
) t. I+ S/ U4 a1 L2 O9 E# Rgenetics.
- \* |- C& C: _+ t# ^An important advance in the past decade is the demonstration that genes9 K/ u$ h& v# N3 {4 C& k; L
that regulate developmental processes in invertebrate species have important
+ ^: K g; C7 ]: h& g( N4 s( Tdevelopmental functions in vertebrates. The wealth of information concerning
* j5 A' a! a8 A# s( Vthe molecular genetic processes that regulate development in various animals: K, ~# v3 v. z2 I7 Q3 J" X; l
demonstrates that developmental programs and biological processes are highly
' V9 Q( k7 D6 M- W( Q6 o% oconserved, albeit not identical, from yeast to human. Indeed, the Human; R0 o% G/ G2 {+ T& @! S
Genome Project has made it possible to identify the homologues in humans/ P" M1 C, U6 e* J) I: n: x
and demonstrate that many of these regulatory genes underlie human developmental3 f1 S# @4 z7 b# J+ L
disorders and aspects of adult diseases in which differentiation processes
& h8 B2 a( w5 p, ]' z3 f4 l( [( I* Lgo awry. Currently, researchers are studying the fundamentals of
( w3 j2 A5 f* D4 }; odevelopmental processes in the appropriate animal model and screening% L" \9 Y" Q' f
humans for mutations in the genes identified by the basic research to be likely. ?8 k9 l8 S9 }% {& W
causative candidates. Researchers are mutagenizing vertebrate animal models c: M' B8 N* ~: G6 O8 q( d
and screening for mutants that resemble known human syndromes. This
6 l* `2 H4 Y6 o. S- S! E! ~cross-fertilization of fields is also impacting concepts in evolutionary biology,4 V) s7 a8 ?) U
xii PREFACE5 u1 q' e+ Z8 P
leading to a better understanding of “ancestral” species via gene expression
! y: e+ l& L3 E! }9 B; c4 Sprofiles, and paradigms in stem cell biology in which naı¨ve cells may be directed& c G6 z( i' H
to “designer” lineages.
* z# I) G2 n* {Most recently, there have been significant technological advances in, }# y, ]1 c( T5 }2 z
genetic, genomic, and protein expression analyses that are having a major
1 j7 p1 x) Q: b$ ]/ [impact on experimental approaches and analytic design. The intersection of. ]% H( j' C+ ]
developmental biology with these technologies offers a new view of developmental
6 U8 t! J/ e/ U* Agenetics that is only beginning to be exploited. It is this new intersection2 ~: w; {; O" {( Q% @
at the onset of the genomic era that is the focus of this book. The book is8 ^7 J& d* C- e& m7 g; E. p: P
organized into sections focused on different aspects of developmental genetics.
1 _9 V% l" T, Y0 @5 xSection I discusses the impact of new genetic and genomic technologies on
9 T, L1 U7 n+ I# Rdevelopment, stem cell biology, evolutionary biology, and understanding1 D3 D$ m" D$ s) O; W' g
human birth defects. Section II discusses several major events in early embryogenesis,9 h1 |. G; b0 O
fate determination, and patterning, including cellular determinants
9 s) y, g' D+ o! {: G5 |8 X(Boveri revisited?), gene cascades regulating embryonic axis formation, signaling6 S" k5 |0 t# c; B8 H6 ~2 E1 K
molecules and transcription factors that regulate pattern formation, and
8 |& B2 j& t- _2 h7 \% d9 Qthe induction of the primary germ layers (ectoderm, mesoderm, and endoderm).) L2 l8 i5 R7 |) m3 x
Section III describes the reorganization of the embryo via different
$ q$ u: Y% ?. stypes of morphogenetic and cellular movements that result in the foundation- x/ i5 r+ R5 c! B/ S2 p8 W
of organ systems, and discusses the many signaling and adhesion molecules* ~2 [. Y r% Y$ w
that are involved in regulating these complex processes. The final three sections# [& J, {" z3 C+ \
focus on the signaling cascades and transcriptional pathways that regulate. p. O# f( H) R' [, h; `
organogenesis in representative systems derived from the embryonic+ _9 b5 ?& e3 ]
ectoderm, mesoderm, and endoderm. These chapters illustrate how embryonic6 T" |4 i0 E3 O/ C3 r4 K
rudiments become organized into adult tissues, and how defects in these processes4 f! k- w) B/ T+ Q4 F3 W! c3 ?/ z
can result in congenital defects or disease. Each chapter demonstrates
6 z& t8 Z9 R) W, [the usefulness of studying model organisms and discusses how this information
5 Q+ _0 B0 o8 N/ ?* Fapplies to normal human development and clinical disorders. Several- }6 @6 t$ A6 Q4 P4 _1 }. H5 G, J- e
chapters also discuss the utility of stem cells to repair damaged organs and
% N0 @& Q2 H+ K+ xthe application of developmental genetics to the manipulation of stem cells
! e; _4 |! }$ k: xfor regenerative medicine.1 _* X2 i _. C- c9 u8 g
The goal of this book is to provide a resource for understanding the critical- b# m4 J$ w0 G/ i5 }8 k
embryonic and prenatal developmental processes that are fundamental to; \: Y+ X8 ] E2 J' O* N
the normal development of animals, including humans. It highlights new8 ^/ |6 D6 j8 c7 E" P
technologies to be used, new questions to be answered, and the important
( g9 U G4 \+ ?9 `! c" proles that invertebrate and vertebrate animal models have had in elucidating
$ f% D( C, ^+ G* `$ n* sthe genetic basis of human development. Developmental genetics has reemerged
: q" m# h% H# n4 y* {% Q" O9 Nfrom its birth a century ago as a nexus of diverse fields that are using y# X) L6 b; w' m: E
the common language of gene sequence and function. This is influencing
8 P8 h, [& a& Swhat questions are posed and how the answers are used. New technologies
' b) M$ [" O* u5 z+ y0 Hare making it relatively easy to study gene expression and regulation at single
) Z+ F) W/ D x G: T1 mcell, tissue, and embryonic levels. The conservation between the genomes
, [3 r7 K7 M4 K1 p+ Rof species that are separated by vast evolutionary time encourages us to) ]6 |& t8 o; f) o8 r% K: p
more fully utilize animal models to gain important insights into the clinical
) Q1 N5 o6 P4 t6 {, X9 Wrelevance of the animal model data. It is our hope that this book will stimulate# S) U1 R/ ?7 d$ f1 Y( |* Z
even more cross-fertilization and interactions between evolutionary biology,' B" A1 ]5 k, D/ Q; `
developmental biology, stem cell biology, basic scientists, and clinical) _& Y4 Q$ ~; O" U
scientists.- S( N/ z! ]8 @" O; T" n6 H6 \
I wish to thank all of the authors for contributing such exciting and/ u2 T5 ?6 r/ v1 F+ Y
excellent chapters, and Pat Gonzalez for keeping all of us on schedule.
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