Fertilization 2N pronucleus (suspended in meiotic metaphase) N polar body reduction division N pronucleus (after sperm enters egg) mitosis 2N zygote nucleus N polar bodies (2): disintegrate membrane formation migrate carrying nutrients N sperm pronucleus fertilization Early establishment of polarity in Drosophila eggs: Maternal genes expressed in follicle cells produce morphogens BICOID maternal effect genes NANOS Anterior Posterior gap genes (transcription factors) -- a class of segmentation gene) 1
cleavage nuclei or energids ANT. Superficial (meroblastic) cleavage POST. ANT. micropyle cytoplasm sperm pronucleus POST. egg pronucleus cleavage center 8-12 synchronized divisions (256-4096 energids) cleavage cells ANT. vitellophage posterior activation P. center pole plasm & cells (primordial germ cells) primary dorsal organ blastoderm differentiation center (end of totipotency) (LONGITUDINAL SECTIONS) vitellophage ANT. germ band POST. posterior activation (proliferation) center Different types of later embryological development (on a continuum) (Holometabola) 1. Short germ band insects Apterygota Orthoptera: Caelifera some Coleoptera (e.g. Tribolium) 2. Intermediate germ band insects Odonata Orthoptera: Ensifera some Coleoptera 3. Long germ band insects (very distinct) Diptera (e.g., Drosophila) Lepidoptera Hymenoptera some Coleoptera 2
Embryonic membrane formation [cross-sections] typical of short / intermediate germ band insects blastoderm amniotic fold germ band (fusion) serosa amniotic cavity embryo (CROSS-SECTIONS) Four general pathways for dorsal closure (puts the inside the embryo) serosa Secondary dorsal organ (serosa) germ band Secondary dorsal organ (serosa) embryo (CROSS-SECTIONS) serosa embryo 3
1a. Invagination (many Coleoptera, etc: short / intermediate germ band insects) Types of gastrulation or endoderm/mesoderm formation vitellophage 2. Overgrowth (Diptera, Lepidoptera, Hymenoptera, & some Coleoptera: long germ band insects) blastoderm inner layer germ band (lateral plates) middle plate (inner layer) 1b. Proliferation or Delamination (other short / intermediate germ band insects, incl. many orthopteroids & Odonata) inner layer (CROSS-SECTIONS) germ band (lateral plates) ventral groove Blastokinesis in short / intermediate germ band insects (Apterygota, Odonata, Orthoptera, some Coleoptera) ANT. POST. head amniotic cavity (dorsal closure) serosa amniotic cavity chorion head (protocephalon) chorion serosa abdomen serosa head thorax & serosa fused head head abdomen (LONGITUDINAL SECTIONS) 4
Blastokinesis in an intermediate germ band insect (Orthoptera: Gryllidae: Acheta) ANT. POST. diagrammatic summary embryo revolution dorsal closure (see previous slide) near hatching (LONGITUDINAL SECTIONS) Segmentation & appendage formation, short germ band insects (Apterygota, caeliferan Orthoptera, some Coleoptera) Zygentoma (Petrobius) Coleoptera (Tribolium) Each segment is added sequentially (Dark bands = proliferation of engrailed mrna) Posterior proliferation zone: continually produces cells immediately anterior to itself. 5
Summary of segmentation & appendage formation in short / intermediate germ band insects (e.g. Ensifera) protocephalon protocorm antenna mouthparts (mandible, maxilla, and labium) Polypod stage labrum labrum antenna eye mouthparts legs legs abdominal appendages Loss of extra appendages late in embryo development protocephalon protocorm antenna mouthparts (mandible, maxilla, and labium) Polypod stage labrum labrum antenna eye mouthparts legs legs too many abdominal appendages morphs into Oligopod stage before hatching 6
Parallel vs. serial/sequential segmentation initial morphogen gradient (long germ band insects) (short / intermediate germ band insects) gap genes segment-polarity genes (e.g. engrailed) pair-rule genes segment-polarity genes (e.g. engrailed) 14 post-cephalic segments 14 stripes No tissue growth Sequential tissue growth Fate map, Drosophila a long germ band insect Polarity, pattern formation, and appendage formation 7
The eight Hox genes of Drosophila (transcription factor genes) Adult labial proboscipedia deformed antennapedia ultrabithorax abdominal-a, -B Order of Hox genes (regulate the development and identity of each region of the body) Embryo Summary of early tissue differentiation oocyte sperm polar nucleus 2 polar bodies ovum with female pronucleus male pronucleus zygote nucleus vitellophage cleavage nuclei (resorbed) pole cells germ cells blastoderm oogonia or spermatogonia ectoderm: stomodeum & proctodeum, neuroblasts & CNS, epidermis & derivatives, respiratory system genital ridges gonads mesoderm: endoderm: midgut muscles, fat body, blood cells & vascular system 8
Hemocoelom, coelom, and mixocoelom Hatching of the egg (eclosion) Bedbug, Cimex sp. (Hemiptera: Cimicidae) Bollworm, Helicoverpa sp. (Lepidoptera: Noctuidae) 9
Hatching by means of a cap Neuroptera: Ascalaphidae Ululodes sp. Post-embryonic development (incomplete/complete metamorphosis) HOLOMETABOLOUS (Lepidoptera) AMETABOLOUS (Zygentoma) HEMIMETABOLOUS (Hemiptera: Heteroptera) 10
Pupal types (Endopterygota/Holometabola) Decticous exarate (Megaloptera: Corydalidae) functional mandibles free appendages Adecticous exarate (Coleoptera, etc.) free appendages Adecticous obtect (Lepidoptera: Sphingidae) Options: Decticous vs. Adecticous; Exarate vs. Obtect glued appendages Secondary return to adecticous exarate: the puparium of higher Diptera and the coarctate pupa Puparium (larval skin) Exarate pupa inside puparium Puparium after eclosion 11
Re-defining instar Origin of the pupa 4 3 2 4 Pharate adult (monarch butterfly) 1 Pro-nymph (Truman & Riddiford) 12