PATH201 L12 Developmental Pathology PDF

PATH201: Developmental Pathology Dr Karen Reader  Oocyte quality & in vitro maturation Intro to me Te Whanganui-a-Tara Sheep oocyte confocal microscopy Sheep oocyte mitochondria Ovarian and prostate cancer Develop...

PATH201: Developmental Pathology Dr Karen Reader  Oocyte quality & in vitro maturation Intro to me Te Whanganui-a-Tara Sheep oocyte confocal microscopy Sheep oocyte mitochondria Ovarian and prostate cancer Developmental pathology – lectures & lab Lecture 12 – Introduction to embryo development Lecture 13 – Overview of developmental pathology Lecture 14 – Developmental pathology: environmental factors Lecture 15 – Developmental pathology: genetic factors Lab 4a & 4b – Developmental pathology: Foetal alcohol spectrum disorder – Zebrafish model (11th & 13th Sept) PATH201: Lecture 12 Introduction to embryo development Learning objectives – introduction to embryo dev Describe the stages of embryo and foetal development Know when key developmental events occur Know which stages are susceptible to developmental anomalies and why Know which organs or body systems are likely to be affected Describe animal and other models used to study human embryology Definitions not specifically examined, but you need to understand these  Ancient Greek teras = “monster” Developmental pathologies Birth defects Congenital anomalies Abnormal development Malformations Includes abnormal structure, function, metabolism or behaviour External/morphological eg. Digital amputations caused by amniotic bands Internal/organ systems/disease eg. Heart defects Or both eg. Down syndrome History of embryology For interest – not examined  Preformationism vs epigenesis from Exercitationes de generatione animalium 1651 by William Harvey Epigenesis theory that an embryo develops progressively from an undifferentiated egg A tiny person (a homunculus) inside a Aristotle (384-322BC) 2000 years earlier sperm, as drawn by Nicolaas Before microscopes invented (late 16th century) Hartsoeker in 1695  Early studies of embryology Engraving by the Leonardo da Klauber brothers Vinci study after drawings by of a foetus Christian Koeck, in a womb from (c. 1510) Soemmerring (1799)  Ernst Haeckel Anthropogenie 1891: comparative vertebrate embryology Lizard Snake Crocodile Turtle Chick Ostrich Opossum Pig Deer Cow Dog Bat Rabbit Human Stages of embryo development From here on is examinable Embryo/foetal development stages Oocyte/sperm maturation Ovulation/ejaculation Fertilisation Implantation Embryo development Foetal development Parturition (birth) https://atlas.eshre.eu/es Human gestation ~38 weeks (post fertilisation) 3 3/4 month-old foetus Human embryology and developmental biology, 6th Edition Carlson, Bruce M.  Human developmental timeline 40 weeks https://embryology.med.unsw.edu.au/embryology  Early embryo development / cleavage / blastulation Week 1 Fertilised Cleaved embryo oocyte – 2 – 4 cell Day 2 pronuclei 44h post IVF 4 cell Blastocyst embryo Day 5 with inner cell mass fragmented trophectoderm cell blastocoel https://atlas.eshre.eu/es Human embryos in culture 3h to 115h post fertilization (4.8 days) Humans hatch too (Day 6-7) expanded blastocyst inner cell mass trophectoderm zona pellucida  Implantation: week 2 (Day 7-9) Mescher AL Junqueira’s Basic Histology: Text and Atlas, 12th edition Gastrulation: week 3 (Day 16-20) Changes embryo from blastula (single layer) to a gastrula (multiple layers of cells) Inner cell mass forms two germ layers Hypoblast = primitive endoderm (extraembryonic cells) Epiblast = embryonic cells Epiblast forms three germ layers Ectoderm (outer layer) Mesoderm (middle layer) Endoderm (inner layer) Cells proliferate, differentiate and move Human embryology and developmental biology, 6th Edition Carlson, Bruce M. Germ layers Internal organs Connective tissues Skin, nerve cells Gastrulation Gastrulation, notochord, somitogenesis: (week 3) Formation of: Neural groove → neural tube Will form brain & spinal cord Somites (balls of mesoderm) ~44 pairs Give rise to connective tissues Somite (cartilage, bone, muscle, tendon) Neural Notochord tube Midline structure Not present in adult Provides patterning signals by secreting sonic hedgehog (shh) Vertebrate body plan complete by end of 4 weeks Begin formation of: Gut tube Liver Genital ridge (ovaries/testes) Neural tube, brain vesicles Heart begins to beat Embryonic period: Weeks 5 to 8 Heart – descends into thorax Lung - buds form, descend into thorax Liver - enlarges Ears – cochlear otic vesicle, external ears form Eyes – retinal pigment present, eye & eyelids develop Limbs - buds form & elongate, hands/feet form, fingers and toes lengthen Brain – cerebellum begins to form Skeleton – 33-34 cartilaginous vertebrae present, ossification of limb bones begins Foetal period: weeks 9 to 38 Organogenesis largely completed (embryonic period) 16 weeks Extensive growth (14 g to 3500 g) Ongoing differentiation and development of the organ systems Three, 3-month trimesters Foetuses born after 22 weeks can survive (15% survival) 7 weeks 28 weeks (90% survival) but 1/3 have significant morbidity Larsen’s Human Embryology 5th Edition When can things go wrong? Oocyte Ex ovo omnia - everything from the egg cellular and molecular mechanisms required for fertilisation and early embryo development are inherent to the oocyte metabolites, organelles and mRNA… “… a prerequisite of obtaining a healthy embryo is first obtaining a healthy oocyte” (Swain and Pool 2008) > 50% of fertilised eggs are lost early in development from Exercitationes de generatione animalium 1651 William Harvey  Oocyte, sperm & fertilisation Oocyte Sperm 1. cumulus expansion motility 2. zona pellucida binding morphology 3. oolemma fusion acrosome concentration 4. oocyte activation 5. sperm processing 6. pronuclear formation Swain, J. E. and T. B. Pool (2008). Human Reproduction Update 14(5): 431-446. Influence of sperm factors on pre-implantation development Mol Hum Reprod, Volume 27, Issue 7, July 2021, gaab042, https://doi.org/10.1093/molehr/gaab042 The content of this slide may be subject to copyright: please see the slide notes for details. Sperm effects on embryo quality Lane, M., et al. (2014). Science 345(6198): 756-760. Early embryo development / cleavage: Week 1 Lane, M., et al. (2014) Science 345(6198): 756-760 Cleavage stage embryo/blastocyst: first 2 weeks Fertilisation, cleavage, blastocyst, bilaminar embryo Exposure to teratogens will usually cause complete loss of the conceptus Abnormalities often result in fertilisation or implantation failure No birth defects as no organs/structures developed yet Or early embryo may compensate for damage (plasticity) Can get subtle effects on long term offspring health high blood pressure insulin resistance/diabetes Main embryonic period: weeks 3 to 8 Gastrulation, embryo folding, formation of organs & systems Active period of development and differentiation Most vulnerable to major birth defects Foetal period: months 3 to 9 Mainly growth of organs & structures already developed Birth defects less severe Small size, mental retardation, defects in eyes, ears, teeth & external genitalia Periods of susceptibility Human Embryology and Developmental Biology, 6th Edition Carlson, Bruce M. How can we study human embryo development? Human embryology research Need to understand how development occurs at tissue, cellular and molecular levels Formation of structures and their function How is it regulated? Which signalling pathways/molecules are involved? What goes wrong? How can we diagnose, prevent and cure birth defects? Which drugs and chemicals are safe for use during pregnancy? How can we improve success rates of ART? Assisted reproductive technologies in NZ 15% couples experience infertility ANZARD report 2021 for NZ 8,861 ART treatment cycles (5,285 in 2010) 22.8% resulted in a live birth (22.6% in 2010) Still very inefficient/poor success rate – why? Evidence of developmental effects, differences in transcriptome etc Need to improve the technology Improve our understanding of normal embryology How to study human embryology - ethics When does life begin? 14-day rule for non-clinical human embryo research HART Act 2004 and ACART guidelines HART Act allows research on human embryos but…. No guidelines for ECART to approve human reproductive research on viable embryos Can’t research ways to improve IVF / ART Minister of Health finally agreed for ACART to develop guidelines in 2022 Public consulted early 2023 https://acart.health.govt.nz/ Goodman, L., L. Cree, D.D.G. Jones, M. Legge, A. Shelling, and C. Farquhar, The futility of fertility research? Barriers to embryo research in New Zealand. N Z Med J, 2018. 131(1477): p. 63-70. Animal models for human embryology Need good model for embryonic period (most susceptible to teratogens) Developmental mechanisms appear well conserved between species, but timing very different Match timing of fertilisation, maternal to zygotic transition, blastocyst, maternal recognition of pregnancy, type of implantation/placentation Animal models have both similarities and differences to human embryo development Best one depends on the research question & developmental stage being studied Don’t know what we don’t know! Animal models for human embryology Non-human primates – most similar, ethical issues and costs Rodents (mouse, rat, hamster) – poly-ovulatory, faster development, cheaper, inbred (less variation), can be genetically modified Domestic animal species (sheep, cow, pig) – mono- or poly-ovulatory, similar timing of development, out-bred (similar variation), placentation different Chicken – faster development, can be manipulated surgically Frog (Xenopus laevis) – external development, large cells, faster development Zebrafish – develop externally, much faster development Sheep – in vitro oocyte, embryo studies Human Comparable size to human oocyte/embryo Similar timing of early development Mainly mono-ovulatory Similar structural, metabolic and transcriptomic profiles Ovaries/oocytes readily obtained from Sheep abattoirs – IVF and in vitro embryo development Can manipulate embryos in vitro then transfer back to ewe Placentation process very different Zebrafish 10 weeks: Fertile adults Large numbers of progeny Embryos are transparent, develop outside the mother Short generation time Fairly cheap and easy 2 days: to raise Free swimming Relatively easy to genetically modify 1 day: Body plan established  Liu, X., et al. (2021). "Modelling human blastocysts by Human iBlastoids reprogramming fibroblasts into iBlastoids." Nature 591(7851): 627-632. Human iBlastoids – are they human embryos? HART Act: embryo includes a zygote and a cell or a group of cells that has the capacity to develop into an individual; but does not include stem cells derived from an embryo Liu, X., et al. (2021) Nature 591(7851): 627-632. iBlastoids from human embryonic stem cells Kagawa, H., et al. (2022).Nature 601(7894): 600-605. iBlastoid implanting into endometrial cell layer Kagawa, H., et al. (2022).Nature 601(7894): 600-605. Summary Stages of development: Fertilisation, cleavage stage, embryonic period, foetal development, birth Know when key developmental events occur: Week 1 Fertilisation, cleavage, blastulation Week 2 Implantation, bilaminar embryo Week 3 Gastrulation, trilaminar embryo Week 4 to 8 Organogenesis Month 3 to 9 Foetal growth and development Summary cont… Periods of susceptibility: Cleavage/early embryo = fertilisation or implantation failure, complete loss Embryonic stage = most susceptible, organs forming Foetal stage = defects less severe, mainly affects growth, some development Animal models and human embryology research Different timing of development, mechanisms similar? Use different models for different stages/questions Suggested reading Robbins Basic pathology 10th edition Chapter 7. Section: Paediatric Diseases; Congenital Anomalies Robbins & Cotran Pathologic Basis of Disease 10th edition Chapter 10. Section: Congenital Anomalies; Definitions, Causes of Anomalies Human Embryology & Developmental Biology 6th edition Chapter 8. up to Section: Causes of Malformations; Genetic Factors, Environmental Factors Any question please email me at [email protected] Extra reading for Lectures 14 & 15 Bull, M. J. Down Syndrome. New England Journal of Medicine, 2020 382:2344-52 Foil, K. E. et al, The increasing challenge of genetic counseling for cystic fibrosis. Journal of Cystic Fibrosis, 2019 18:167-174 George, S. et al. Molecular aspects of the teratogenesis of rubella virus. Biological Research, 2019 52:47