Lecture 2 BIO3147 (2024).pdf

Figure 8.3 Summary of the main patterns of cleavage Figure 8.3 Summary of the main patterns of cleavage (Part 1) Figure 8.3 Summary of the main patterns of cleavage (Part 2) Figure 8.5 A summary of the cell movements represented during gastrulation Figure 8.5 A summary of the cell movements represen...

Figure 8.3 Summary of the main patterns of cleavage Figure 8.3 Summary of the main patterns of cleavage (Part 1) Figure 8.3 Summary of the main patterns of cleavage (Part 2) Figure 8.5 A summary of the cell movements represented during gastrulation Figure 8.5 A summary of the cell movements represented during gastrulation (Part 1) Figure 8.5 A summary of the cell movements represented during gastrulation (Part 2) Figure 8.5 A summary of the cell movements represented during gastrulation (Part 3) Figure 8.6 Cross-sectional drawings by Ernst Haeckel (A) and Élie Metchnikoff (B) of the progressive stages of embryogenesis from a single cell to gastrulation (top to bottom) Cross-sectional drawings by Ernst Haeckel (A) and Élie Metchnikoff (B) of the progressive stages of embryogenesis from a single cell to gastrulation (top to bottom). (A) Haeckel’s illustrations of the cell behaviors in organisms such as amphioxus were presented in support of his theory that gastrulation evolved by way of invagination. (B) Metchnikoff’s drawings of a developing sea urchin were presented in support of his competing theory that gastrulation evolved via ingression. [Both dudes were right!] Figure 8.5 A summary of the cell movements represented during gastrulation (Part 4) Figure 8.5 A summary of the cell movements represented during gastrulation (Part 5) Figure 8.5 A summary of the cell movements represented during gastrulation (Part 6) Figure 1.11 The dividing cells of the fertilized egg form three distinct embryonic germ layers Figure 1.6 Axes of a bilaterally symmetrical animal Figure 1.12 The fates of individual cells Edwin Conklin mapped the fates of early cells of the tunicate Styela partita using the fact that in embryos of this species many of the cells can be identified by their different-colored cytoplasms Figure 1.12 The fates of individual cells (Yellow cytoplasm marks the cells that form the trunk muscles) (A) At the 8-cell stage, two of the eight blastomeres contain this yellow cytoplasm. (B) Early gastrula stage, showing the yellow cytoplasm in the precursors of the trunk musculature. (C) Early larval stage, showing the yellow cytoplasm in the newly formed trunk muscles. Figure 1.14 Vital dye staining of amphibian embryos Figure 1.13 Fate mapping using a fluorescent dye (A) Specific cells of a zebrafish embryo injected with a fluorescent dye that will not diffuse from the cells. The dye was then activated by laser in a small region (about 5 cells) of the late-cleavage-stage embryo. (B) After formation of the central nervous system had begun, cells that contained the activated dye were visualized by fluorescent light. The fluorescent dye is seen in particular cells that generate the forebrain and midbrain. (Similar in C and D) Figure 1.14 Genetic markers as cell lineage tracers Genetic markers as cell lineage tracers. (A) Experiment in which cells from a particular region of a 1-day quail embryo have been grafted into a similar region of a 1-day chick embryo. After several days, the quail cells can be seen by using an antibody to quail-specific proteins (photograph below). This region produces cells that populate the neural tube. Figure 1.14 Genetic markers as cell lineage tracers (B) Chick and quail cells can also be distinguished by the heterochromatin of their nuclei. Quail cells have a single large nucleus (dense purple), distinguishing them from the diffuse nuclei of the chick. (C) Chick resulting from transplantation of a trunk neural crest region from an embryo of a pigmented strain of chickens into the same region of an embryo of an unpigmented strain. The neural crest cells that gave rise to the pigment migrated into the wing epidermis and feathers. Figure 1.15 Fate mapping with transgenic DNA shows that the neural crest is critical in making the gut neurons (A) A chick embryo containing an active gene for green fluorescent protein expresses GFP in every cell. (B) The region of the neural tube and neural crest in the presumptive neck region (rectangle in A) is excised and transplanted into a similar position in an unlabeled wild-type embryo. Figure 1.18 The vertebrates—fish, amphibians, reptiles, birds, and mammals—all start development very differently because of the enormous differences in the sizes of their eggs. By the beginning of neurulation (shown below), however, all vertebrate embryos have converged on a common structure. Figure 1.18 The vertebrates—fish, amphibians, reptiles, birds, and mammals—all start development very differently because of the enormous differences in the sizes of their eggs. By the beginning of neurulation (shown below), however, all vertebrate embryos have converged on a common structure. As they develop beyond this neurula stage, the embryos of the different vertebrate groups become less and less like each other. Table 1.2 von Baer’s laws of vertebrate embryology (Ontogeny & Phylogeny) Figure 1.12 Evolution of pharyngeal arch structures in the vertebrate head (A) Embryonic pharyngeal arches (also called branchial arches) (B) In adult fish, pharyngeal arch cells form the hyomandibular jaws and gill arches. (C) In amphibians, birds, and reptiles (a crocodile is shown here), these same cells form the quadrate bone of the upper jaw and the articular bone of the lower jaw. (D) In mammals, the quadrate has become internalized and forms the incus of the middle ear. The articular bone retains its contact with the quadrate, becoming the malleus of the middle ear. Figure 1.12 Evolution of pharyngeal arch structures in the vertebrate head Thus, the cells that form gill supports in fish form the middle ear bones in mammals. Figure 1.18 Larval stages reveal the common ancestry Larval stages reveal the common ancestry of two crustacean arthropods, barnacles (A) and shrimp (B). Barnacles and shrimp both exhibit a distinctive larval stage (the nauplius) that underscores their common ancestry as crustacean arthropods, even though adult barnacles—once classified as mollusks—are sedentary, differing in body form and lifestyle from the free-swimming adult shrimp. A larva is shown on the left in each pair of images, an adult on the right. What do we have in common with sea squirts? Tunicate (urochordate; wikipedia ) Amphioxus (cephalochordate; wikipedia) Larval stage of the ascidian tunicate C. intestinalis reveal its common ancestry with other chordates. Station Biologique Roscoff Ciona intestinalis (Adult form) Linnaeus grouped sea squirts (tunicates) as mollusks (1767) Dorsal nervous system and a notochord (Kowalevsky 1866) What do we have in common with sea squirts? Corbo et al., 2001 Phylogenetics first confirmed that sea squirts were chordates (left) and then demonstrated that they are the closest invertebrate relative to vertebrates! (right) This means that tunicates lost somites, which cephalochordates and vertebrates have Delsuc et al., 2006 Figure 1.20 Transitional states over the course of animal evolution (Part 2) (B) A late Jurassic (~150 mya) fossil of Archaeopteryx showing its distinctive features of both a reptilian skeleton and avian feathered wings. Figure 1.20 Transitional states over the course of animal evolution (Part 3) (C) Tiktaalik roseae emerged 375 mya from the water to be the first animal hypothesized to walk on land. This fossil (upper) and reconstruction (lower) revealed characteristics of both fish fins and amphibian forelimbs, among other characteristics. [found in Nunavut, Canada by Daeschler, Shubin, and Jenkins] Figure 1.23 The tree of life—an illustration of the major branches of life Figure 1.21 Homologies of structure among a human arm, a seal forelimb, a bird wing, and a bat wing; homologous supporting structures are shown in the same color Homology of structure among a human arm, a seal forelimb, a bird wing, and a bat wing; homologous supporting structures are shown in the same color. All four limbs were derived from a common tetrapod ancestor and thus are homologous as forelimbs. The adaptations of bird and bat forelimbs to flight, however, evolved independently of each other, long after the two lineages diverged from their common ancestor. Therefore, as wings they are not homologous, but analogous. Figure 1.22 Development of bat and mouse forelimbs (Part 1) Pentadactyl groundplan Figure 1.22 Development of bat and mouse forelimbs (Part 2) Figure 1.22 Development of bat and mouse forelimbs (Part 3) (C) Comparison of mouse and bat forelimb morphogenesis Both limbs start as webbed appendages, but the webbing between the mouse’s digits dies (apoptosis) at embryonic day 14 (arrow). The webbing in the bat forelimb does not die and is sustained as the fingers grow. Figure 1.24 The developmental evolution of life This illustration depicts key developmental adaptations that occurred over the course of evolutionary history in animals. The last eukaryotic common ancestor (LECA) gave rise to both plants and animals 2000 million years ago (mya). (1)Colonization of choanoflagellate cells. (2) Development of a 2-layered organism with a proliferative inner layer and an epithelial filter-feeding outer layer. (3) Digestive architectures emerge with the evolution of tighter junctions and extracellular matrix (neon blue). (4) A primitive gut with aboral and oral openings appears, as in the sponge. (5) Ctenophores, such as this comb jelly, exhibit the first interconnected system of nerve-like cells. (6) Cnidarians such as the sea anemone show the first signs of gastrulation. (7) Bilateral symmetry evolves (aceols) and (8) segmentation emerges, generating (9,10) a diversity of arthropod lineages. (11) Adaptation of mesoderm produces the first axial derivative—the notochord (red)—giving rise to chordates. (12–14) From jawless fish (12, lamprey) to jawed fish (13, teleost) and from paired fins to articulating forelimbs (14, Tiktaalik), metazoans walk out of the water. (15,16) Among the terrestrial tetrapods, reptiles (15) further adapt their forelimbs into wings, giving rise to avian species (16). Remarkable complexity of development (Amphibian)