1、Insect Physiology Developmental Systems,Department of EntomologyNational Chung Hsing University,CONTENTS,Preembryonic development 胚胎前發育Insect eggsEgg membranes 卵膜Pattern formation within the oocyte 卵決定作用Embryonic developmentBlastoderm formation 囊胚形成Formation of the germ band 胚帶形成Blastokinesis and do
2、rsal closure 轉胚動Formation of the gut 腸化作用Formation of the nervous system 神經系統形成Formation of internal organs 內部構造形成Formation of the reproductive system 生殖系統形成Endocrinology of embryonic development 內分泌學,Preembryonic Development,All multicellular organisms begin their lives as single-celled zygotes tha
3、t divide to form groups of cells that show progressive 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 morphological differences and the genera
4、tion 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 membrane with a thickness of about 0.3 mmWax layer腊層: 5 nm to 2 mm; to provide protection against desiccationChorionic laye
5、rs:Inner chorionic layer Endochorion: inner and outer endochorionExochorion,Cross-Section of an 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
6、plastron to extract 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 Oocyte,There are distinct regions with an oocytePeriplasm: cytoplasm i
7、mmediately beneath the plasma membraneSpatial gradient of protein that result from the transcription of specific genes to create a pattern that provides the developing embryo with positional information within the egg.Morphogens,Polarity Gradients of Morphogens,Polarity gradients of these materials
8、are established early during oogenesis, while the oocyte resides in 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 Egg,Fig. The
9、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 Drosophila oocyte.,Insect Egg Prior to Fertilization,The oocyte, which has been arrested in me
10、taphase of the first meiotic division, continues to mature after oviposition occurs.Shortly after the sperm penetrates the egg 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 inter
11、ior of the egg.Parthenogenesis: reproduction 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 complete cleavage. (e.g. mammals)Meroblasti
12、c 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. insects),Blastoderm Formation,Energid: each nucleus surrounded by a small island of cytoplasm during the meroblastic cleav
13、age of most insectsAfter a series of mitoses, the energids migrate to the egg periphery and continue 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; giv
14、e rise to the germ 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 blastoderm.,Fig. Formation of the cellular blastoderm from th
15、e syncytial blastoderm.,Formation of the Germ Band,Embryonic primordium: the thickened portion of the blastoderm; develop into the embryoExtraembryonic ectoderm: the other cells of the blastoderm beside the primordiumGerm line: the embryonic primordium increases in length; represents the ventral reg
16、ion of the future body,Fig. Development of the embryonic permordium and extraembryonic 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 groove
17、: 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 constitutes the trunk of the developing insect,Fig. Formation of mesoderm from the migrati
18、on of ectodermal cells.,Origin of the Mesoderm from Cells Expressing Twist,Segmentation,Segmentation begins as the maternal effect genes activate or repress the gap genes to establish regions of segment identity.The concentrations of Bicoid, Hunchback, and Caudal proteins determine the transcription
19、 patterns of the gap genes. The produces of the gap 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 ultimately produce the anterior compart
20、ment 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 each of the parasegments.Then, subsequent interactions of the gap and pair-rule genes regulate the homeotic gene
21、s that establish the identity of each segment and its characteristic structure. (next slide),Blastokinesis 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
22、 amniotic folds.Amniotic 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 closure: after blastokinesis and growth of the embryonic ectoder
23、m 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 it from the serosa.,Fig. The formation of neuroblasts from ectodermal tissue and the proliferation of mesoderm.,Fig. Dorsal closure of the e
24、mbryo.,Formation of the Gut,Cells at the anterior and posterior ends of the embryo 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 the yo
25、lk 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 ectodermal invaginations and the development of endoderm that forms the midgut.,Form
26、ation of the Nervous System,The nervous system arises from ectodermal cells in the ventral region of the germ band.Proliferation of the neuroblasts in portions of the embryonic ectoderm produces a neural groove and neural ridges.Three groups of neuroblasts that proliferate in the anterior region ult
27、imately produce the procerebrum, deutocerebrum, and tritocerebrum 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 rise to most of the internal
28、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 constructed around the pole cells.The pole cells become the germ cells of the future adult. The genital ridge of mes
29、oderm that forms the reproductive organs, germaria of the ovarioles and the follicles of the testes.Mesoderm 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 mat
30、ure insect.,Endocrinology 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: involved in embryonic molting.Juvenile hormone: less kno
31、wn about its contributions during embryogenesisDiapause hormone in Bombyx mori eggs,Two Way to Create a Morphogen Gradient,The Origins of the Drosophila Body Segments 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 Phenotypes of Mutations Affecting the Three Types of Segmentation,The Regulatory Hierarchy of Egg-Polarity, Gap Segmentation and Homeotic Selector,
