CONTENTS
Main Page Dynamic Development
The Foundations of Developmental
Biology
Gametogenesis
From Sperm and Egg to Embryo
Genetic Regulation of Development
Organizing the Multicellular
Embryo
Generating Cell Diversity
Dynamic Development at a
Glance |
Overview of Amphibian Development
by Leon W. Browder and Becky Wong
Xenopus laevis, the South African Clawed Frog
Now that you have practiced using the Internet to obtain developmental
biology resources, you should be able to use that skill to explore the virtual
world of development, with The Virtual Embryo as your guide. We want to
focus on two concepts simultaneously throughout this course: the diversity
of developmental programs and the similarities among basic developmental
processes. We're going to start with an overview of amphibian development,
using The Amphibian Embryology Tutorial, developed by Dr. Jeff Hardin at
The University of Wisconsin. At this time, we are not going to utilize the
entire tutorial, but we are going to focus on pages that describe the major
early developmental events. We shall return to other topics in this rich
resource later.
Carefully examine the links below, but make sure you only look at the first
page of that link, unless otherwise instructed. When you have completed
the page, use the "back" button at the upper left-hand corner
of the Netscape window (do not use the "main menu" navigation
bar at this point). You may return to this page by pressing the "back"
button on the upper left corner of the window or by selecting Amphibian
Development in the "Go" pull-down menu.
Welcome to
the Amphibian Embryology Tutorial: This link introduces you to
this tutorial.
Oogenesis:
The highlighted links on this page take you to the glossary, which provides
a definition of that term. These links do not need to be accessed
unless you require the definition. The movie (oogen.MOV) shows
the process of oogenesis, with the animal pole at the top, and the yolk
becoming localized in the vegetal hemisphere at the bottom.
The Full-grown
Oocyte
Fertilization
Cleavage:
There are six pages to be reviewed once you have entered this link.
These pages are accessed by clicking on the red arrow symbol at the top
of this page. There is a movie to be viewed on the Radial vs. Spiral
Cleavage page (rad_spir.mov).
Gastrulation:
There are 19 pages to be studied. Again, use the red arrow symbol
at the top of the page to take you to the next page. To get back to
this page, use the "back" button on Netscape or use the "Go"
command. Consult your textbook for additional details on gastrulation.
- Introduction: Movie-nieuwkoop2.mov. This
movie shows gastrulation happening from the vegetal pole view. The
cells of the outer layer envelops the yolk cells of the lower half.
Midway through this movie, the blastopore is formed, and gastrulation continues.
- Morphogenic Movements
- More Morphogenic Movements
- Fate Mapping: This link requires for you to review the
highlighted numbers 1-4 to trace how the vital dyes were used to follow
the movements of cells as gastrulation proceeds.
- Gastrulation Time-Lapse: Movie-xlgast.mov.
Compare this movie to the nieuwkoop2.mov movie; these two movies
show the same processes, but in different perspectives.
- Sagittal View: Movie-wholegas.mov. Note the
movement of the yolk within the gastrula as convergence and extension by
the outer cells form the blastopore.
- Surface Fate Map: Movie-superfic.mov. Note
the yellow ectoderm invaginates as the presumptive epidermis covers the
outer gastrula.
- Deep Fate Map: Movie-deepmap.mov. Notice
the movement of the leading edge mesoderm.
- Fate Maps of Urodeles vs. Xenopus
- Epiboly of the Animal Cap
- Apical Constriction of Bottle Cells: Click on the boxes
the look at the the three views of the bottle cells.
- 1. Onset of apical constriction
2. Blastoporal groove
3. Rolling of blastoporal lip
- DIMZ: Movie-dimx2.mov.
- Relationship Between DIMZ and Other Tissue: Movie-i_nimz.mov.
- Keller Sandwich
- Types of Keller Sandwiches
- Keller Sandwich Behaviour: Movie-sandwich.mov.
- Behaviour in "Open Faced" Sandwiches: Movie-openface.mov.
- Leading Edge Mesoderm
- Migratory Cues for Leading Edge Cells
Neurulation:
We shall examine a dorsal view of a neurula-stage embryo. Note the distinct
nature of the "notoplate" of the neural tube, which is also known
as the "floor plate". It is anchored to the notochord, which is
located just below it.
Neurulation
Time-lapse: Movie-keller_gast.mov. This movie begins
the same as xlgast.mov (gastrulation time-lapse movie), BUT the process
advances through to neurulation.
Meanwhile, much has been happening internally. We shall be examining internal
morphogenesis in more detail later. However, to give you a feel for the
internal morphology of the embryo, we shall now examine cross-sections of
the Rana embryo at a stage that is roughly comparable to stage 23
in Xenopus. Initially, you should study
the embryo in depth by examining the material prepared by Dr. Steven
Scadding at The University of Guelph at his Web site, Developmental Biology
ONLINE. Read his home page CAREFULLY as it instructs you on how to
navigate his site. Click "Go to the site" icon to view the
37 photographs and familiarize yourself with the new terminologies.
Now, you should examine a video of the 4mm
frog embryo (produced by Dr. Laurie Iten, Purdue University). The video
can be played both forward and backward and can be stopped at any point.
You should navigate through the embryo to get a feel for the structural
continuity.The cross-sections are shown sequentially, beginning anteriorly
and moving toward the rear end. You can manipulate the video so that you
can examine any region of the embryo in more detail. |
