Developmental Genetics Dr E M Honey Department Genetics

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Developmental Genetics Dr. E. M. Honey Department Genetics University of Pretoria

Developmental Genetics Dr. E. M. Honey Department Genetics University of Pretoria

Main events in the development of a human infant Pre-embryonic First cell division Zygote

Main events in the development of a human infant Pre-embryonic First cell division Zygote reaches uterine cavity Implantation Formation of bilaminar disc Lyonization in female Formation of trilaminar disc Closure of the neural tube 30 hours 4 days 5 -6 days 12 days 16 days 19 days 24 days

Main events in the development of a human infant Embryonic stage Organogenesis 4 -8

Main events in the development of a human infant Embryonic stage Organogenesis 4 -8 weeks Brain and spinal cord are forming 4 weeks First sign of heart and limb buds Brain, eyes, heart and limbs developing 6 weeks Bowel and lungs begin to develop Digits have appeared Ears, kidneys and muscle are developing 8 weeks Palate closes and joints form 10 weeks Sexual development almost complete 12 weeks

Main events in the development of a human infant Fetal stage Fetal movements felt

Main events in the development of a human infant Fetal stage Fetal movements felt Eyelids open Fetus now viable with special care Rapid weight gain due to growth and Accumulation of fat as lungs mature 16 -18 weeks 24 -26 weeks 28 -38 weeks

Tissue origins • Ectoderm Central nervous system Peripheral nervous system Epidermis including hair and

Tissue origins • Ectoderm Central nervous system Peripheral nervous system Epidermis including hair and nails Subcutaneous glands Dental enamel • Mesoderm Connective tissue Cartilage and bone Smooth and striated muscle Cardiovascular system Urogenital system • Endoderm Thymus and thyroid Gastro-intestinal system Liver and pancreas

Genes involved in the developmental process • Gene and gene families identified in the

Genes involved in the developmental process • Gene and gene families identified in the fruit fly Drosophila melanogaster • Produces transcription factors - controls RNA transcription from the DNA template by binding to specific regulatory DNA sequences - switch genes on and off by activating or repressing gene expression - regulating fundamental embryological processes

Genes involved in the developmental process • Mutations in various members of these gene

Genes involved in the developmental process • Mutations in various members of these gene families can result in either isolated malformations or multiple congenital anomaly syndromes • Examples: Segmentation genes, Homeobox genes, Pairedbox(PAX) genes, SRY-type HMG box(SOX) genes, Tbox(TBX) genes, Zinc finger genes, signal transduction(“signalling”) genes.

Genes involved in the developmental process • Segmentation genes: Sonic Hedgehog, Desert Hedgehog and

Genes involved in the developmental process • Segmentation genes: Sonic Hedgehog, Desert Hedgehog and Indian Hedgehog - left-right asymmetry, polarity in the CNS, organogenesis and formation of the skeleton • Homeobox genes: 39 identified, embryo can’t survive • Homeobox-like domain: MSX 2(craniosynostosis) and EMX 2(schizencephaly) • Paired-box(PAX) genes: 9 identified - PAX 3 – Waardenburg syndrome - PAX 2 – renal-coloboma syndrome - PAX 6 – aniridia(WAGR syndrome)

Genes involved in the developmental process • SRY-type HMG Box(SOX) genes – role in

Genes involved in the developmental process • SRY-type HMG Box(SOX) genes – role in male sexual determination - SOX 9 on Chr 17 causes camptomelic dysplasia - SOX 10 on Chr 22 causes Waardenburg syndrome associated with Hirschprung didease • T-BOX(TBX) genes - role in mesoderm formation and notochord differentiation - TBX 3 causes ulnar-mammary syndrome - TBX 5 causes Holt Oram syndrome

Genes involved in the developmental process • Zinc finger genes – complex of 4

Genes involved in the developmental process • Zinc finger genes – complex of 4 amino acids which form a complex with a sinc iron - GLI 3 on chr 7 – deletions causes Greig cephalopolysyndactily, frameshift mutations causes Pallister-Hall syndrome • Signalling genes – implicated in cancer - RET proto-oncogene causes Hirschprung disease - Fibroblast growth factor receptors

Fibroblast growth factor receptors Craniosynostosis syndromes FGFR 1 8 p 11 FGFR 2 10

Fibroblast growth factor receptors Craniosynostosis syndromes FGFR 1 8 p 11 FGFR 2 10 q 25 FGFR 3 Skeletal dysplasia FGFR 3 4 p 16 Pfeiffer Apert Crouzon Jackson-Weiss Pfeiffer Crouzon Achondroplasia Hypochondroplasia Thanatophoric dysplasia

Limb as a developmental model • 4 main phases: 1. Initiation – FGF 2,

Limb as a developmental model • 4 main phases: 1. Initiation – FGF 2, 4 or 8 2. Specification - HOX genes limb type 3. Tissue differentiation – SHH, HOXA, HOXD 4. Growth – FGF genes important

Sexual differentiation • X and Y chromosomes • SRY gene – transcription regulator •

Sexual differentiation • X and Y chromosomes • SRY gene – transcription regulator • Mutations XY females • Crossover XX males • Other genes plays a role e. a. SOX 9

XIII Developmental Genetics XIII Developmental Genetics A OverviewXIII Developmental Genetics XIII Developmental Genetics A Overview
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