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本帖最后由 细胞海洋 于 2010-11-30 12:27 编辑 5 p; }0 c1 T8 g/ k
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Developmental Genetics, or What Can Genetics and Genomics Tell Us About Evolution, Development, Stem Cells, Human Birth Defects, and Disease?
& D% x1 _( V* Z# k; O4 p/ b2 Y7 o, F0 g8 _ n3 y
The ability of researchers to answer experimental questions greatly depends& f4 z# f% |! A4 E4 N
on the available technologies. New technologies lead to novel observations
, K; z9 k$ d1 u- Gand field-changing discoveries and influence the types of questions that can
5 F6 o4 j& d9 g& \9 z; W c9 cbe asked. Today’s recently available technologies include sequencing and analyzing
! A9 y7 T, V5 x! p; hthe genomes of human and model organisms, genome-wide expression
, k- f3 R/ q* e1 Zprofiling, and high-throughput genomic and genetic analyses. The information+ W) O- N+ M4 R& ~5 {& d
provided by these approaches is enabling us to begin to understand the) Q9 {; S3 V0 E- E$ ~
complexity of many biological processes through the elucidation of gene regulatory8 d- M9 C" q2 j' t# L
networks, signaling pathway networks, and epigenetic modifications.
/ p7 Y' U' k4 ]This book describes many lines of research that are being impacting by these
( V0 y! c- l2 }$ _9 L0 P; ?new technologies, including developmental genetics and the related fields of; [$ Q0 Y# p/ Y9 v1 u
clinical genetics, birth defects research, stem cell biology, regenerative medicine,
% g- y5 j K1 u3 t' f6 t9 tand evolutionary biology.! P8 Y* s; ~$ b# u4 l" R
The field of developmental genetics, or the study of how genes influence
8 E, I+ A; P0 E+ X8 i$ Pthe developmental processes of an organism, has been influenced by new technologies5 ^0 Z* T+ b- y4 B
and by interactions with other fields of study throughout its history.) M" C6 ~. u$ K% t. p- h9 n
The concept of a genetic basis of development began in “modern” times at the
: n4 [% _) X' u! |5 a( Lintersection of descriptive embryology and cytology. Modern histological5 J2 ]: n. F1 {6 Q0 E
techniques were developed in the mid-19th century, largely by Wilhelm His. A3 `3 H- g' ^' E# z1 i. W
so that he could study cell division in the neural tube, which enabled visualization
- g# Q6 Q; T3 @of the cell nucleus, chromosomes, and the discrete steps of mitosis.& Z* q$ D, i. q% i& Y
Theodor Boveri cleverly applied these improved microscopic techniques to% ]: |4 R+ `" L' d9 o8 _
transparent marine embryos to demonstrate that each parent contributes0 o/ [$ {' s' n; t3 K
equivalent groups of chromosomes to the zygote, and that each chromosome$ Z w9 N4 |5 o
is an independently inherited unit. Importantly, he noted that if an embryo) [( k7 h+ ?% A) h4 U/ V
contains the incorrect number or improper combination of chromosomes, it
6 Q Y' N! v! N$ |7 \develops abnormally.! Z- v" }9 v, f
However, many early embryologists rejected the idea that development is! ^, \, X/ U# w$ D2 l! H7 c
driven by prepackaged heritable particles because it seemed too similar to the
6 c7 ]. W) F- U+ p5 Nidea of “preformation”: the concept that development is driven by predetermined
7 v& D+ X6 O8 [& C* {9 a4 Pfactors or “forces” (sometimes described in rather mystical terms).
4 G! ^8 F: ~, V2 qWilhelm Roux, an advocate of studying the embryo from a mechanistic point) T8 N" m- s/ o- [
of view, was a leader in the approach of manipulating the embryo with microsurgical
. u& O7 B+ t, g& A' v) |techniques to elucidate cause and effects between component parts$ I' n8 p, S& T; f6 V/ W0 `5 O
(experimental embryology). By using an animal model whose embryos were( V3 h+ z P: H+ g
large, developed external to the mother, could be surgically manipulated with% {" e& M; r6 `- z% f
sharpened forceps and cultured in simple salt media (i.e., amphibians), he
( [8 b* v5 a- O. \! U7 L! s; krejected the role of predetermined factors and demonstrated the importance$ T4 {- ~1 \4 l$ i5 W' l. a
of external (epigenetic) influences and cell–cell interactions in regulating" S* y# c2 {6 ~9 R
developmental programs. Experimental embryologists further refined their
0 Q! x+ d0 T1 H5 G4 I0 k& Wskills at dissecting small bits of tissue from the embryo, recombining them
# Z" L# P, `4 ^& ~* Z1 N! Jwith other tissues in culture or transplanting them to ectopic regions in the& |+ G/ p. p) x* Q9 i
embryo. This work led to the invention of tissue culture by Ross Harrison- B2 E* f' O. f3 G7 y% _% b, t
and the discovery of tissue inductions by Hans Spemann., p4 U5 z0 C m. R* [
While experimental embryology was thriving, T. H. Morgan founded the
$ X( Y, J2 ~9 u' L& } d- Jfield of Drosophila genetics. Also trained as an embryologist, Morgan was8 n5 t3 l; Z# O# W( w# h1 ~
skeptical of Boveri’s idea of heritable packets, and directed his studies towards ?- b- A& p `* X
understanding the principles of inheritance. For several decades, the two fields) N1 E3 B$ n% |5 w1 F1 C6 v2 S
had little impact on one another. Interestingly, however, after a few decades of/ p- O4 E S/ `. c
study of the fruit fly, Morgan’s work supported the idea of discrete intracellular
% I) g. g' _2 X2 z) Jparticles that directed heritable traits, which he named “genes.” Nonetheless,2 f W7 ` I' M2 S/ G, u: F. w
the fields of experimental embryology and genetics remained fairly. o; }8 [5 [ E" K8 j
separate entities with distinct goals and points of view. Embryologists were, p: I7 z: c1 ^% [+ \
elucidating the interactions that are important for the development of numerous
# R0 k8 O3 x8 ~9 M5 x4 B7 s8 ztissues and organs, whereas geneticists were focused on the fundamentals
D5 S* Y8 W2 aof gene inheritance, regulation of expression, and discovering the genetic0 h* l# \$ \- @/ O+ J( S
code. Indeed, elucidating the genetic basis of vertebrate development was. \: n N: f7 e" J( I
delayed until new technologies in molecular biology and cloning were devised.0 B- ~% U5 D Q
From the field of bacterial and viral genetics came the techniques for cloning
- ~/ o6 @7 ^; H( `* S) c& Yeukaryotic genes and constructing vectors for controlling expression. From, e( n; z0 B1 H- c E
the classical genetic studies in fly and nematode came the rationale for mutagenizing: V1 v7 q8 X$ W+ ^4 M- W
the entire genome and screening for developmental abnormalities.
' a% ]6 c8 U# o1 D7 hImportant regulatory genes were discovered in these invertebrates, and their9 g, E) i" H1 V6 A2 R# k
counterparts were discovered in many other animals by homology cloning1 D/ R6 u6 ?; T$ e5 @# a
approaches. Thus was born the modern field that we call developmental7 }6 t9 @$ W- Y, `4 e; N
genetics.4 U0 t3 ?) B- G- z4 \* t' G
An important advance in the past decade is the demonstration that genes
; [% o7 D: d o3 b* L/ M8 P" `+ Tthat regulate developmental processes in invertebrate species have important. J2 M. ?/ H5 R6 s% K& D! n
developmental functions in vertebrates. The wealth of information concerning Y' l$ D$ Z0 [
the molecular genetic processes that regulate development in various animals2 R, F2 a# c! P
demonstrates that developmental programs and biological processes are highly( U' u. o) k) \6 g& V
conserved, albeit not identical, from yeast to human. Indeed, the Human
8 @; E' k, m8 {1 V6 jGenome Project has made it possible to identify the homologues in humans: ^9 W/ e" J, f. @( {
and demonstrate that many of these regulatory genes underlie human developmental! J( Z6 R. Z% f
disorders and aspects of adult diseases in which differentiation processes' B" o; S) a2 {- f. h$ d3 F
go awry. Currently, researchers are studying the fundamentals of
' \0 d' U' k' T& a8 T# kdevelopmental processes in the appropriate animal model and screening
8 b* e. {" Z4 x3 U+ K4 J. q5 e/ ~, B8 xhumans for mutations in the genes identified by the basic research to be likely. K# O( h) t/ p1 U" n7 }
causative candidates. Researchers are mutagenizing vertebrate animal models
% F+ _3 [* K& vand screening for mutants that resemble known human syndromes. This4 p1 G+ i4 C* e8 ^, ]1 f
cross-fertilization of fields is also impacting concepts in evolutionary biology,
5 {/ [/ A0 c; Z8 `! Lxii PREFACE
7 E$ D+ f5 ?' C: e$ ~leading to a better understanding of “ancestral” species via gene expression2 l& h9 G1 y0 t; U
profiles, and paradigms in stem cell biology in which naı¨ve cells may be directed
: F( K1 n, N4 {) A$ S7 e G# X( o1 ?# mto “designer” lineages.
/ z4 t+ F! Y4 j. w9 D- q. CMost recently, there have been significant technological advances in" ]6 O0 p9 k) a
genetic, genomic, and protein expression analyses that are having a major1 _% {$ J+ j% V) J) u( [4 O u3 D7 g
impact on experimental approaches and analytic design. The intersection of
- ~( t# h/ [* K* |$ Ndevelopmental biology with these technologies offers a new view of developmental* S7 ?8 W3 H6 f" X' \. M
genetics that is only beginning to be exploited. It is this new intersection
" J; `" T$ Q5 u0 G' [at the onset of the genomic era that is the focus of this book. The book is) v- L# r5 }% a o( Z
organized into sections focused on different aspects of developmental genetics.
9 Q! K0 L( L- ], v1 P# O' QSection I discusses the impact of new genetic and genomic technologies on( U% g7 B9 V3 J/ z! b* D
development, stem cell biology, evolutionary biology, and understanding
Q& q# g5 f s% t* y2 ? Ahuman birth defects. Section II discusses several major events in early embryogenesis,
! i7 p8 ]) C7 [$ V1 N" Afate determination, and patterning, including cellular determinants
& C f8 y* m7 V9 u- i/ [" a0 C(Boveri revisited?), gene cascades regulating embryonic axis formation, signaling
3 b9 n$ E% e( {molecules and transcription factors that regulate pattern formation, and7 _& H* z0 J' ]; _+ z2 E9 y* E
the induction of the primary germ layers (ectoderm, mesoderm, and endoderm).
4 V5 T% t# z+ aSection III describes the reorganization of the embryo via different# {9 o$ h4 q( g0 q3 C' P
types of morphogenetic and cellular movements that result in the foundation
5 s* c* T. c; c: L5 [2 O/ ^$ tof organ systems, and discusses the many signaling and adhesion molecules# g4 a6 P# x1 o
that are involved in regulating these complex processes. The final three sections8 F6 }& n0 s# j5 y( o' }( D6 n
focus on the signaling cascades and transcriptional pathways that regulate/ ]- w! K% W3 W' ]1 d( O* T1 O' C* D
organogenesis in representative systems derived from the embryonic1 f4 q F* t( [0 b, t2 k/ U& l0 ?$ O
ectoderm, mesoderm, and endoderm. These chapters illustrate how embryonic
; S7 E) ]/ B$ J* Q2 `rudiments become organized into adult tissues, and how defects in these processes
. p7 |6 A9 I, c0 Y2 j2 Lcan result in congenital defects or disease. Each chapter demonstrates. `) }& C0 h7 ]
the usefulness of studying model organisms and discusses how this information
* T0 U, M2 X4 N7 Capplies to normal human development and clinical disorders. Several
1 W4 G2 j7 D$ b- A" o4 R. Echapters also discuss the utility of stem cells to repair damaged organs and e. b8 \. F. Z! b* u) a" M7 @2 F8 R
the application of developmental genetics to the manipulation of stem cells
M! X8 y' M3 ` q. D! Z. t: lfor regenerative medicine.7 F6 Z; C4 T+ S! e9 K9 P) E
The goal of this book is to provide a resource for understanding the critical
1 n1 r5 r' S' Z; u! Cembryonic and prenatal developmental processes that are fundamental to! @- N' m7 u4 D- ]' C6 G0 E
the normal development of animals, including humans. It highlights new
3 k, ~, k6 e' _' w* ztechnologies to be used, new questions to be answered, and the important& G7 T1 K! |6 ]) {2 H$ P
roles that invertebrate and vertebrate animal models have had in elucidating
* h& N% T/ ~; }8 [, d& Uthe genetic basis of human development. Developmental genetics has reemerged5 L" N; L# t, I) ~+ U. m8 n3 ^
from its birth a century ago as a nexus of diverse fields that are using, k6 S1 j3 z! |) ]$ j0 V
the common language of gene sequence and function. This is influencing
. g/ f" O! h7 H% p( Gwhat questions are posed and how the answers are used. New technologies
# e5 A& W# }+ c5 c4 l. ?& `are making it relatively easy to study gene expression and regulation at single
" F H- C( |% V+ Ycell, tissue, and embryonic levels. The conservation between the genomes! E: c2 L v3 D: F- b
of species that are separated by vast evolutionary time encourages us to, x4 I* _; ?8 r( o" {; Y# V: K
more fully utilize animal models to gain important insights into the clinical
4 S* l/ l3 O: g6 }& G% u: s jrelevance of the animal model data. It is our hope that this book will stimulate7 \, ]" c5 f+ |5 @/ n }
even more cross-fertilization and interactions between evolutionary biology,
f% M g# s! b- Qdevelopmental biology, stem cell biology, basic scientists, and clinical
! W. c# ^) `5 Q9 B( W3 x0 Ascientists.
0 l0 M! z! `+ y8 _I wish to thank all of the authors for contributing such exciting and
. {' r- P, S6 Xexcellent chapters, and Pat Gonzalez for keeping all of us on schedule.
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