The term embryogenesis, or embryonic development, refers to all those processes that lead to the development of the embryo starting from the fertilized or activated egg.
Embryogenesis is an orderly sequence of growth, differentiation and organogenesis phenomena that leads to the formation of an individual.
Embryogenesis therefore takes place following fertilization, i.e. the fusion of the two gametes and, therefore, of the genetic material coming from the two parents.
Fertilization induces the egg thus activated to begin its development process and the sequence of successive stages takes the name of embryogenesis.
In general, albeit with small differentiations, embryogenesis is divided into the following stages:
– the first is segmentation, ie that process of rapid mitotic divisions in which the volume of the cytoplasm divides into smaller cells, called blastomeres, which generally form a sphere called blastula. The blastomeres undergo movements by which they change their position with each other. This phase is called gastrulation and consists of numerous and different cellular modifications which will lead to the formation of three layers of embryonic cells, called germ layers. The ectoderm is the outer layer, the mesoderm the middle layer, while the inner layer is called the endoderm. The cells of the epidermis and nervous tissue will originate from the ectoderm, the various internal organs (such as the heart and kidney, connective tissue and blood cells) from the mesoderm, while the cells of the internal lining will originate from the endoderm. of the digestive tract and the organs derived from it (such as the liver and pancreas).
– the stage that leads cells to interact and reorganize themselves to form the various organs of the body is called organogenesis and, in Vertebrates, begins with a series of specific cellular interactions. These interactions will induce the middorsal ectoderm cells to form the neural tube that will become the brain and spinal cord. One of the first cellular differentiations that occur during embryogenesis also concerns the separation of germ cells from somatic cells: the former migrate towards the gonads, where they differentiate into gametes through a process called gametogenesis.
Embryogenesis is a process that also affects the plant world where, although it is not the usual path of a microspore, this process is the most effective way to produce haploid and double haploid plants through the use of male sex hormones.
Under certain stress factors such as heat or hunger, plants select microspores for embryogenesis. Over 250 different angiosperm species were found to have responded in this way. In the anther, after a microspore undergoes microsporogenesis, it may deviate towards embryogenesis and become star-shaped microspores. The microspore can then go one of four ways: become an embryogenic microspore, undergo callogenesis at organogenesis (plant haploid/double haploid), become a pollen-like structure, or die.
Microspore embryogenesis is used in biotechnology to produce double haploid plants, which are immediately fixed as homozygous at each locus in just one generation. The haploid microspore is prompted to trigger the pathway of embryogenesis and the resulting haploid embryo doubles its genome either spontaneously or with the help of chromosome doubling agents. Without this double haploid technology, conventional breeding methods would require several generations of selection to produce a homozygous line.