25. Comparative development II

25. Comparative development II - 3/27/12 Announcements...

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Unformatted text preview: 3/27/12 Announcements – Friday in PLS 1140 at 9 and 10 AM Exams returned at end of class Life’s Fundamental Processes – Structure and Function Relationships Development Gas exchange Circula-on (intercellular transport) Nutrient uptake Osmoregula-on and excre-on Communica-on (electrical signaling) Mo-lity, biomechanics, and locomo-on Compara-ve Development II Previous class – 1. Homeobox genes encode for transcrip-on factors 2. Hox genes specify segment iden-ty along the A ­P axis in animals 3. Other homeobox genes trigger the pathways for organ development  ­ some examples? 4. Useful concept of gene-c toolkit Each Fundamental Process of Life Unity of Life Universal physical and chemical principles Diversity of Life places design constraints on provides certain opportuni-es for and/or Common genomic toolkit from LUCAC Ecological roles Organismal strategies provides molecular solu-ons for can evolve for selec-on pressures Compara-ve Development II Different cells, -ssues, & organs 1 3/27/12 Life’s Fundamental Processes – Structure-Function Relationships Typical Approach – separate units on how each group of organisms accomplishes all processes, OR 207 Approach – separate units on how each process is accomplished by all groups For example, nutrient uptake: 1. Universal physical and chemical principles – cation electrochemical gradients 2. Common genomic heritage resulting in “deep molecular homology” of transport proteins 3. Unique structures for carrying out function in different lineages – pseudopodia, hyphae, roots, small intestines, etc. 4. Special emphasis on complex organ systems in animal/ vertebrate/human lineages – digestive systems Molecular mechanisms of eukaryotic development 1.  Homeobox genes encode for transcrip-on factors 2.  Homeobox – 180 nucleo-de mo-f within a larger gene 3.  Homeodomain (60 amino acids)  ­ helix ­turn ­helix structure composed of 3 α ­helices with short loop regions 4.  Recogni-on helix, plus unstructured N ­terminus, recognize promoter sequences of important developmental genes 5.  Hox genes– homeobox genes encoding for the A ­P axis of animals Some themes in the comparative development of eukaryotes 1. Enormous flexibility in bilaterian design  ­ > 30 modern phyla with dis-nc-ve body plans, o\en u-lizing homologous molecular mechanisms 2.  Why study the development of other eukaryotes? Fascina-ng examples of biological diversity Deep insights into the evolu-on and mechanisms of bilaterian development Recruiting of homeobox genes to control eukaryotic development A few homeobox genes in most pro-st genomes, including ma-ng ­type genes– gamete ­specific plus (gsp) gamete ­specific minus (gsm) Chlamydomonas life cycle 1.  The origins of the molecular mechanisms for regula-ng mul-cellular development 2.  The origins of death – the separa-on of reproduc-ve cells (the germ cells) from vegeta-ve cells (the “soma”) 2 3/27/12 Evolu-on of symmetry of mul-cellular animals Evolution of developmental processes in basal metazoans Colored boxes = hox genes One growth axis  ­ top to bo2om See F. Fig. 32.5 Bilateral symmetry Two growth axes  ­ anterior to posterior (AP) dorsal to ventral (DV) Radial symmetry No symmetry Planes of symmetry = number of so ­called mirror images Peterson and Davidson (2000) PNAS 97:4430 ­4433 Cambrian Radiation C & R Fig. 32.13 Sudden appearance of the ancestors of modern bilaterian phyla around 545-530 MYA 3 3/27/12 Symmetry  ­ plants Cambrian Radiation “ecological arms race”new large predators, new protective shells/ endoskeletons Animals  ­ phylogene-c switch from radial to bilateral symmetry Plants  ­ persistent radial symmetry of main and lateral axes, with repeated evolu-on of bilateral leaves Early land plant sporophytes Most living plants  ­ aboveground structures Bryophytes Radial axes (stems)  ­ specialized for support and transport Bilateral organs (leaves)  ­ specialized for photosynthesis Vascular plants Silurian plants (400 mya) Apical meristem – growing -p of ~100 cells Early land plant sporophytes  ­ “naked” axes with no leaves Radial symmetry comes from hemispherical apical meristem that represents the growing -p of the shoot axis Shoot apical meristem – generates new stem ­leaf modules 4 3/27/12 Basic principles of plant development Evolu-on of land plant symmetry RS  ­ radial symmetry MAM  ­ mul-cellular apical meristems L  ­ bilateral leaves (at least four -mes) RS – ancestral condi-on L – photosynthe-c adapta-on L L L L MAM RS Gene-c regula-on of shoot apical meristems Background: Apical Meristems give rise to the en-re plant body: New cells for maintaining the meristem New cells for differen-a-ng organs Animals – determinate organisms – cell differentiation and organ formation occurs within defined body Plants – indeterminate organisms – new cells, organs, and meristems develop throughout the life span SAM = shoot apical meristem RAM = root apical meristem Gene-c basis of early plant evolu-on: Homologous homeobox genes, different developmental func-on mitosis Zygote (2n) OR Zygote  ­ ­ ­ ­ ­ ­ ­ ­ ­ ­> Sporophyte (2n) (charophyte) (plant) Charophyte zygote – gsp/gsm heterodimer acts as transcrip-on factor for controlling the expression of meiosis genes KNOTTED1-like homeobox genes (KNOX) control the transcription of other genes for maintaining meristematic state. Other genes, such as ASYMMETRIC LEAVES1 (AS1), suppress the expression of KNOX genes, resulting in the initiation of leaves. Plant zygote – gsm homolog (KNOX) acts as transcrip-on factor for controlling the expression of shoot apical meristem genes Co ­opted gsm func-on to construct the sporophyte 5 3/27/12 Gene-c regula-on of floral organs Molecular mechanisms of eukaryotic development 1.  MADS ­box genes encode transcrip-on factors. MADS (four names of 2 plant, 1 yeast, and 1 human genes) 2.  MADS box – 165 ­180 nucleo-de mo-f within a larger gene 3.  MADS domain (55 ­60 amino acids) – long α ­helix 4.  DNA recogni-on  ­ paired, an- ­parallel helices from two MADS ­domain proteins ac-ng as a dimer 5.  Many eukaryotes, but mostly plant development, esp. flowering Model plant Arabidopsis C & R F of Polar view ig.35.35a floral meristem Wild ­type flower Polar view of mature flower F Fig. 22.11 Whorl 1 2 3 4 B genes A genes C genes Organ Se Pe St Ca Zhongchi Li (CBMG) Gene-c regula-on of floral organs Whorl 1 2 3 4 Summary  ­ ABC Model for Gene-c Regula-on of Floral Organs Three classes of MADS ­box genes act as transcrip-on factors for regula-ng floral development B genes A genes C genes Organ Se Pe St Ca A class by itself directs sepal forma-on A + B classes direct petal forma-on B + C classes direct stamen forma-on C class by itself direct carpel forma-on ABC model for floral inducOon C & R Fig.35.35a Whorl 1 2 3 4 AP3/PI AP1/AP2 ABC model for floral inducOon AG Organ Se Pe St Ca ABC model for floral inducOon Wild ­type flower C & R Fig.35.35b Gene-c reasoning Can you use the ABC model to predict the phenotypes of several floral mutants? C & R Fig. 35.36 A class = APETALLA1/APETALLA2 B class = APETALLA3/PISTILLATA C class = AGAMOUS How would you test the model? 6 ...
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This note was uploaded on 04/05/2012 for the course BSCI 207 taught by Professor Higgins during the Spring '08 term at Maryland.

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