Overview of Amphibian Development

Xenopus laevis, the South African Clawed Frog

Now that you have practiced "surfing the Net" (aren't you sick and tired of that expression?), you should be able to use that skill to explore the virtual world of development, with that silly grinning frog 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.

Note: There are a number of movies on these pages. If you are in the Mac lab, please view them from copies that have been saved on the hard drive of your machine. This will save you a considerable amount of time. They are located in a folder entitled amphibian, which - in turn - is in the dev biol folder. If you need assistance, please ask your TA.

Welcome to the Amphibian Embryology Tutorial
Oogenesis
The Full-grown Oocyte
Fertilization
Cleavage. Use the "Forward" button to navigate through all of the cleavage pages. Return here when you have studied all of them.

We shall now examine a critical stage in Xenopus development, the mid-blastula stage. We shall discuss the significance of this stage extensively during this course. This drawing is from the classical Nieuwkoop and Faber staging series.
Stage 8

Returning now to the Amphibian Embryology Tutorial,...
Gastrulation
Fate Mapping
Gastrulation Time-lapse
Neurulation
Neurulation Time-lapse

We shall now take a look at progressive stages of neurulation in Xenopus from the Nieuwkoop and Faber staging series. Note how the neural folds elevate on the dorsal surface of the embryo and fuse to form the neural tube. Initially, the neural folds are continuous laterally with presumptive skin ectoderm. The anterior end of the neural tube enlarges to form the brain.
Stage 12.5
Stage 14
Stage 16

In the next image, you will be looking head-on at an embryo in which the neural folds are touching one-another. Below the neural folds is a darkened structure that will form the cement gland. This is an important developmental marker.
Stage 19 (anterior)

A dorsal view of the same stage is shown next
Stage 19 (dorsal)

A lateral view of a stage 23 embryo is shown next. The neural tube has completely closed by this stage. The protrusion of the eye vesicle can be seen clearly, and the jaw- and gill-areas are separated by a groove. The location of the anal opening can be seen. Posterior to it, the tail bud primordium is evident.
Stage 23 (lateral)

Meanwhile, much has been happening internally. We will be examining internal morphogenesis in more detail later. However, so as 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. 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.
4mm frog embryo (produced by Dr. Laurie Iten, Purdue University).

If you are in the Mac lab, a full-size version of this video has been down-loaded on the hard drive of your machine. It can be located in the folder entitled dev biol. Use the video in conjunction with your lab manual to understand how components of the embryo relate to one-another spatially. In preparation, be sure to read carefully the text portion of your lab manual describing the embryology of 4-mm frog embryos. The video can be played both forward and backward and can be stopped at any point. Initially, you should navigate through the embryo to get a feel for the structural continuity. Next, you should stop at sections comparable to those in Plates 1-4 in Schoenwolf and identify the labeled structures. Once you have identified these structures, move backward and forward to see how they change along the length of the embryo. Be also aware how the structure you have identified relates to other structures around it.

A lateral view of a much later stage of Xenopus development is shown next. At this stage, the eye and ear vesicles and the gill promordia are prominent, as are the outlines of the somites and pronephros in the trunk region. The tail fin is quite extensive.
Stage 28