anoverviewofinsecthormones-國立中興大學(xué)昆蟲系

1、Insect Physiology Developmental Systems,Department of EntomologyNational Chung Hsing University,CONTENTS,Preembryonic development 胚胎前發(fā)育Insect eggsEgg membranes 卵膜Pattern formation within the oocyte 卵決定作用Embryonic d

2、evelopmentBlastoderm formation 囊胚形成Formation of the germ band 胚帶形成Blastokinesis and dorsal closure 轉(zhuǎn)胚動Formation of the gut 腸化作用Formation of the nervous system 神經(jīng)系統(tǒng)形成Formation of internal organs 內(nèi)部構(gòu)造形成Formation of

3、the reproductive system 生殖系統(tǒng)形成Endocrinology of embryonic development 內(nèi)分泌學(xué),Preembryonic Development,All multicellular organisms begin their lives as single-celled zygotes that divide to form groups of cells that show pr

4、ogressive morphological changes.Two main processes occur in the embryonic development Determination決定作用: the commitment process that establishes the later differentiated stateDifferentiation分化作用: the development of mo

5、rphological differences and the generation of cellular diversity,,Insect Egg Structure,Egg Membranes,Chorion卵殼: synthesized within the ovariole by the follicular epitheliumVitelline envelope卵黃膜: an inner noncellular mem

6、brane with a thickness of about 0.3 mmWax layer臘層: 5 nm to 2 mm; to provide protection against desiccationChorionic layers:Inner chorionic layer Endochorion: inner and outer endochorionExochorion,Cross-Section of an

7、 Drosophila Egg,Specialized Structures of Insect Eggs,Micropyle受精孔: an opening of chorion that allows a single sperm to enter. (some with many micorpyles)Respiratory appendages: structures that serve as a plastron to e

8、xtract oxygen from water.Operculum卵蓋: a cap that is surrounded by hatching regions and opens to allow the larva to exit.,Cross-Section of an Insect Egg,Respiratory Horns of Drosophila Egg,,Pattern Formation within the

9、Oocyte,There are distinct regions with an oocytePeriplasm: cytoplasm immediately beneath the plasma membraneSpatial gradient of protein that result from the transcription of specific genes to create a pattern that prov

10、ides the developing embryo with positional information within the egg.Morphogens,Polarity Gradients of Morphogens,Polarity gradients of these materials are established early during oogenesis, while the oocyte resides in

11、 the female even before fertilization and oviposition occur (next slide)Maternal effect genes: establish an anterior-posterior polarity in the egg, such as bicoid, nanos, hunchback, and caudal,Cross-Section of an Insect

12、 Egg,Fig. The mechanism of Gurken signaling to establish anterior/posterior and dorsal/ventral commitment of follicle cells.,Fig. The gradients of bicoid, nanos, hunchback, and caudal mRNA that establish position in the

13、Drosophila oocyte.,,Insect Egg Prior to Fertilization,The oocyte, which has been arrested in metaphase of the first meiotic division, continues to mature after oviposition occurs.Shortly after the sperm penetrates the e

14、gg and oviposition take place, the oocyte completes meiosis.,Insect Egg Prior to Fertilization,Syngamy: the union of sperm pronucleus and oocyte pronucleus; occurs at the interior of the egg.Parthenogenesis: reproductio

15、n without sperm involvement; a haploid polar nucleus combines with the haploid oocyte nucleus to restore the diploid.,Egg Cleavage,Holoblastic cleavage: animals that have relatively little yolk are able to undergo comple

16、te cleavage. (e.g. mammals)Meroblastic cleavage: the relatively large amount of yolk prevents the first cleavage divisions from cutting through the entire egg, and their cleavage is more superficial cleavage. (e.g. inse

17、cts),Blastoderm Formation,Energid: each nucleus surrounded by a small island of cytoplasm during the meroblastic cleavage of most insectsAfter a series of mitoses, the energids migrate to the egg periphery and continue

18、to divide there.Syncytial blastoderm: lacks any membranes, with all the cleavage nuclei contained within the common cytoplasm.Pole cells: some of the energids migrate to the posterior of the egg; give rise to the germ

19、cells.Vitellophages: some energids remain in the yolk; involved in the digestion of yolk and the formation of the midgut epithelium.,Fig. Migration of energids to the periplasm of an insect oocyte, forming the syncytial

20、 blastoderm.,Fig. Formation of the cellular blastoderm from the syncytial blastoderm.,,Formation of the Germ Band,Embryonic primordium: the thickened portion of the blastoderm; develop into the embryoExtraembryonic ecto

21、derm: the other cells of the blastoderm beside the primordiumGerm line: the embryonic primordium increases in length; represents the ventral region of the future body,Fig. Development of the embryonic permordium and ext

22、raembryonic ectoderm from the blastodermal cells.,Gastrulation,Gastrulation: the germ band develop to become a double-layer embryoThe cells of the germ band migrate inward into yolk to form a multicellular layerGastral

23、 groove: the longitudinal furrow that is formed by the elongation and migration upward of the cells along the ventral line midline of the germ bandMesoderm: the inner layer of cells of the gastal groove.The germ band c

24、onstitutes the trunk of the developing insect,Fig. Formation of mesoderm from the migration of ectodermal cells.,Origin of the Mesoderm from Cells Expressing Twist,Segmentation,Segmentation begins as the maternal effect

25、genes activate or repress the gap genes to establish regions of segment identity.The concentrations of Bicoid, Hunchback, and Caudal proteins determine the transcription patterns of the gap genes. The produces of the g

26、ap genes regulate the expression of the pair-rule genes.The produces of the pair-rule genes further divide the broad gap gene regions into individual parasegments. (next slide),Segmentation,The parasegments will ultimat

27、ely produce the anterior compartment of one segment and the posterior compartment of the next.The segment polarity genes assure that certain repeated structures appear in each segment, establishing the cell fates within

28、 each of the parasegments.Then, subsequent interactions of the gap and pair-rule genes regulate the homeotic genes that establish the identity of each segment and its characteristic structure. (next slide),,Blastokinesi

29、s and Dorsal Closure,Amniotic folds: the folds which are formed while the germ band elongates and widens, carrying the margin of the extraembryonic ectoderm with it.Amnion: the inner walls of the amniotic folds.Amnioti

30、c cavity: the amnion enclosureSerosa: the ectoderm that is detached from the germ bandBlastokinesis: the movements of the germ band within the yolk; reverse the relative positions of the yolk and the embryoDorsal clos

31、ure: after blastokinesis and growth of the embryonic ectoderm over the dorsal portion and end up with to enclose the yolk within the embryo.,Fig. The formation of the amnion and the invagination of the germ band to free

32、it from the serosa.,Fig. The formation of neuroblasts from ectodermal tissue and the proliferation of mesoderm.,Fig. Dorsal closure of the embryo.,,Formation of the Gut,Cells at the anterior and posterior ends of the emb

33、ryo migrate inward to form the foregut, hindgut, and midgut.Foregut and hindgut: raise from ectoderm cells.Midgut: from the endoderm (some of the invaginating epithelia)The endodermal cells form sheets that enclose th

34、e yolk in a tube that creates the midgut epithelium. Vitellophages contained within the yolk that are integrated into the endoderm to form the definitive midgut epithelium.,Fig. Formation of the foregut and hindgut from

35、ectodermal invaginations and the development of endoderm that forms the midgut.,,Formation of the Nervous System,The nervous system arises from ectodermal cells in the ventral region of the germ band.Proliferation of th

36、e neuroblasts in portions of the embryonic ectoderm produces a neural groove and neural ridges.Three groups of neuroblasts that proliferate in the anterior region ultimately produce the procerebrum, deutocerebrum, and t

37、ritocerebrum of the brain. Those in other segments give rise to the subsesophageal and abdominal ganglia.,Fig. Formation of the ventral nerve cord from neuroblasts.,,Formation of Internal Organs,Mesodermal tissue gives r

38、ise to most of the internal organs of the insect.Splanchic mesoderm: forms the visceral musclesSomatic mesoderm: gives rise to the skeletal muscles,,Formation of the Reproductive System,The reproductive system is const

39、ructed around the pole cells.The pole cells become the germ cells of the future adult. The genital ridge of mesoderm that forms the reproductive organs, germaria of the ovarioles and the follicles of the testes.Mesode

40、rm also gives rise to the lateral oviducts and vasa deferentia.Invaginations of the ectoderm form the median oviduct and ejaculatory duct.,Fig. Cell lineages and derivation of tissues in the mature insect.,,Endocrinolog

41、y of Embryonic Development,Hormones required during embryogenesis are packaged into the egg largely as inactive hormone conjugates and released from the conjugates as active hormones when they are required.Ecdysteroids

42、: involved in embryonic molting.Juvenile hormone: less known about its contributions during embryogenesisDiapause hormone in Bombyx mori eggs,Two Way to Create a Morphogen Gradient,The Origins of the Drosophila Body S

43、egments During Embryonic Development,A Drosophila oocyte in Its Follicle,The Organization of the Four Egg-Polarity Gradient Systems,Morphogen Gradients Patterning the Dorsoventral Axis of the Embryo,,Examples of the Phen