THE BLASTOPORE BECOMES THE MOUTH SKIN
THE BLASTOPORE BECOMES THE MOUTH PLUS

(Photo: EMBL)ДЄlthough a homologue of dpp, bmp-4, was found and cloned in frog embryos, scientists did not find a parallel between insect morphogenesis and vertebrate embryos. Detlev Arendt, European Molecular Biology Laboratory in Heidelberg. In the amphioxus lancelet (Branchiostoma lanceolatum), a primitive deuterostome regarded as a model of the ancestors of vertebrates, there are 10 Hox genes, mice and humans have 38 arranged in four clusters that developed through duplication. Scientists found that the same homologous gene cassette also occurs in other animals, although the number of Hox genes varies. It is slightly confusing that these segments do not correspond with the developing segments of the fly. Each of the genes is expressed in particular body segments. Drosophila has eight Hox genes that are arranged in linear order on the chromosome. The proteins encoded by the Hox genes either directly or indirectly control the transcription of numerous genes, including those that are responsible for the formation of typical features in the individual embryo segments. The Hox genes were initially discovered in Drosophila and have a typical sequence of approximately 180 base pairs (homeobox), which encode a particular DNA-binding region.

THE BLASTOPORE BECOMES THE MOUTH PLUS

One of the most important discoveries of modern evo-devo research (evolution plus development) is that the embryonic longitudinal axis in animals develops according to the same principle, i.e. Conserved genes during embryonic development

THE BLASTOPORE BECOMES THE MOUTH SKIN

They differ from other phyla because they shed their skin (Greek: Ecdysis) during individual development. The arthropods (insects, crayfish, spiders, centipedes, etc.) and other relatives are nowadays grouped as Ecdysozoa together with the unsegmented nematodes (ring worms like for example the favourite experimental animal of molecular biologists, Caenorhabditis elegans). This classification can be seen as a late triumph for the classical developmental biologists or embryologists, who suggested a big similarity between Trochophora larvae and marine annelids and snails. Nowadays, they are grouped as Lophotrochozoa, together with molluscs. Previously, scientists thought that annelids (bristle worms) were related to arthropods due to their segmentation. In terms of the division of major phyla, the molecular data suggest some radical changes. Of course, there were also some new views: A few invisible candidates вЂ“ such as Brachiopoda and Bryozoa вЂ“ which were often regarded as deuterostomes, now count as protostomes. The frog's egg is very dark and it is difficult to apply vital dyes so that they will be visible on the frog blastula.It was possible to confirm this basic division of the animal kingdom into protostomes and deuterostomes by modern analyses used in molecular phylogeny. In deuterostome development, the blastopore becomes the animal's anus.ДЄ fate map is simply a topographical surface mapping of the blastula with respect to the ultimate fate of the various areas. In protostome development, the first opening in development, the blastopore, becomes the animal's mouth. Similarly, you may ask, what does the Blastopore develop into? The upper hemisphere of the egg - the animal pole - is dark. During embryonic development, the egg will be converted into a tadpole containing millions of cells but containing the same amount of organic matter. Secondly, what is an embryo of a frog? The frog egg is a huge cell its volume is over 1.6 million times larger than a normal frog cell. The blastocoel probably serves two major functions in frog embryos: (1) it permits cell migration during gastrulation, and (2) it prevents the cells beneath it from interacting prematurely with the cells above it. Similarly one may ask, what is the fate of Blastocoel in the embryo of starfish and frog? Cells migrate through the blastopore and toward the animal pole (Figure 2.3A,B). Gastrulation in the frog begins at a point on the embryo surface roughly 180 degrees opposite the point of sperm entry with the formation of a dimple, called the blastopore.

The blastopore becomes the mouth