Lecture_7_G.ppt

Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. (1) (2 pts) Sperm are specialized for what functions (discuss at least two)? (2) (2 pts) What are the developmental consequences of a therapeutic treatment that blocks the interaction between the sperm and ZP3 in the zona pellucida? Why does this happen? (3) (2 pts) What is the developmental relationship between the zygote nucleus and the sperm pronucleus?   (4) (1 pt) If a spermatogonium undergoes 4 mitotic divisions at which time its progeny enter prophase I of meiosis, what is the maximum number of spermatozoa produced that could potentially fertilize an egg? ____________ (5) (1 pt) What would be the developmental consequence of a change in the pH of the female genital tract that inhibited sperm motility? ____________________ Study Guide for Lecture #6: Plant Development Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Reading: Pg. 225-231; 232-236; 246-250 Arabidopsis thaliana as model for plant development - diploid (many plants are polyploid) - life cycle is relatively short - small genome ? 25,000 genes It is hard to think like a plant ? nevertheless they are very important There are about 350,000 species Autotrophic (mostly) and source of energy for animals (heterotrophic) Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Embryogenesis in Arabidopsis Egg divides to generate multicellularity (cleavage) - Oriented cell divisions generate inside-outside layer of tissue organization (similar to end result of animal gastrulation) Basal cell is equivalent to extraembryonic tissues and the apical cell goes on to form the embryo Oriented cell divisions give rise to embryonic cotyledons (seed leaves ? energy at germination) - Two populations of undifferentiated cells (apical meristems ? one at each end) Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Fate Map It is easy to see since the cells do not move around ? so the position at birth determines the location as development progresses (if cells get displaced into a different layer, their fate is changed, i.e. determination of cell fate is a consequence of location, which in turn is a consequence of cell history) Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Germination - At the end of embryogenesis, development arrests ? - Environmental cues trigger germination Radish seed germination http://www.youtube.com/watch?v=d26AhcKeEbE Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Vegetative grow (most of plant development) occurs post-embryonically and is modular Plants have remarkable regenerative abilities Can grow a whole plant from a cutting Can grow from callus formation (cloning at the cellular level) by dedifferentiation of somatic cells (a callus is equivalent to a regenerating limb blastema) Regeneration by callus formation appears to be a recapitulation of embryonic development (they form embryoids ? that end up looking more or less like early embryos) - Maternal factors and determinants cannot be required since can grow from a single cell - Plant cells are either simultaneously differentiated and multipotent or they can easily be reprogrammed to acquire multipotency Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Clonability allows for transgenesis Agrobacterium tumefaciens (causes crown gall disease) transforms plant cells with the Ti plasmid that has been engineered to introduce transgenes without being pathogenic (you can transform Arabidopsis by dipping their flowers into a broth of Agrobacterium, the seeds produced will be transgenic) Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Development of the plant occurs after germination of the embryo and is a consequence of growth and patterning of the cells of the meristems Series of repeating modules where shoot meristem grows and periodically gives off a lateral outgrowth which is also a meristem (lateral shoot meristem) - Get internode (growth from shoot meristem) and nodes (genesis of lateral shoot meristem and leaf)   Meristem is organized by ?organizing center? that creates the microenvironment to keep cells undifferentiated and to maintain them as stem cells (self-renewing) - Meristem population size is maintain by feedback signaling Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Mutations in progenitor cells result in variegation   Variegation allows for lineage analysis and the inference of the number of progenitor cells Hard to visualize this in animals (e.g. calico cats) ? but is important to recognize the relationship between the early embryonic cells (just a few cells) and the final pattern (many cells) Although constraints of cell division generate mosaic patterns, the fate of cells is determined by where they end up (environmental cues) ? cells that are displaced between populations adopt the fate of the new location Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. The observation that 1/3 of the leaves are mutant leads to the inference that there were 3 founder cells - Floral meristem gives rise to floral organ primordia - 4 whorls of primordia The identity of each whorl is specified by overlapping domains of expression of homeotic genes that function as transcription factors Lots of diversity in floral patterns between plant species, but the mechanism by which the pattern is specified is conserved The germ lineage is not set apart from the somatic lineage Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. The vegetative shoot meristem is converted into the floral meristem Plants have homeotic mutations in homeotic genes ? Not the same genes (plants also have genes with homeobox) However, they regulate pattern by overlapping expression domains They have a conserved DNA binding domain (MADS domain) just like the homeodomain (homeobox) of HOX genes in animals Although the genes are different, many of the mechanisms are remarkably similar Raises the issue of what we mean when we use the word ?mechanism? ?Mechanism? and ?gene? are not synonymous Genes are part of the mechanism and the mechanism is how the cells behave in response to changes in gene expression Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Lecture 7 Concepts to understand/Questions to answer 1 ? Early plant embryogenesis involves cleavage to generate a multicellular embryo 2 ? Most of plant development is post-embryonic and derived from continuously dividing progenitor populations of undifferentiated, pluripotent cells ? the meristems 3- Division of meristem cells is regulated by cells of the organizing center (equivalent to the stem cell niche in animals) 4 ? There is essentially no cell migration ? morphogenesis occurs by regulation of the plane of cell division 5 - Fixed lineage leads to variegation 6 ? Plants have remarkable regenerative abilities 7 - Regeneration occurs by dedifferentiation (reprogramming) of somatic cells 8 - The germ lineage is not set apart from the somatic lineage 9 ? Plant and animal development share similar mechanisms (e.g. flower pattern formation), but use different genes 10 - ?Mechanism? and ?gene? are not synonymous Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. Winter 2011, Bio 104, K. Arora, K. Cho and D. Gardiner, UCI - Copyright: All rights reserved. (1) (0.5 pts) ____T/F______ Plant somatic cells are totipotent. (2) (2 pts) What is the developmental relationship between the shoot apical meristem and the floral meristem? (3) (0.5 pts) ___T/F_____A plant somatic cell can be used to clone the vegetative part of the plant but not the germ cells of the plant. (4) (2 pts) What is the developmentally relevant relationship between sperm and pollen? Study Guide for Lecture #7: