Gene control of differentiation in ontogeny

Gene control
Fertilization produces a zygote from the two gametes, and a morula from the grooving one. As the cells travel out, a blastula is formed and then a gastrula (three germ layers) is formed. This is followed by the development of the primitive streak, organogenesis and histogenesis.

During ontogeny, the following mechanisms apply:


 * cell growth, cell division, migration cells,
 * differentiation cells,
 * apoptosis.

All cells in the body have the same set of genes, but differ in their expression.

Ontogenesis = sequence of events that is initiated by fertilization - regulatory cascade (local mediators, hormones, receptors, transcription factors, etc. are used here)

Morphogenes = control the differentiation and predetermination of cells, their action depends on the concentration of their products - they create a concentration gradient where the effect occurs only from places where the concentration reaches a certain threshold level. Their cascade is already activated before fertilization

Maternal Way Genes

 * They are part of the mother's genome,
 * expressed in follicular bb and their mRNA and proteins transported to the egg,
 * in their mutations, the zygote dies independently of its genotype,
 * they determine the anterioposterior and dorsoventral polarity of the embryo,
 * this includes bicoid (determines where the front of the embryo is) and nanos (determines the back of the embryo),
 * works in collaboration with hunchback gene.

Segmentation genes

 * In vertebrates, the segments are distinct only in the initial stages of development.

Gap genes



 * E.g. hunchback, knirps, giant a krüpl,
 * genes of maternal origin are activated,
 * their mutation: developmental disorder of part of the segments,
 * they are transcription factors,
 * affect the basic differentiation of the embryo.

HOX genes

 * They contain a homeodomain (homeobox)
 * Their mutations can cause one organ to be confused with another,
 * bithorax and antenapedia complex genes,
 * mutation of the antenapedia gene in Drosophila melanogaster causes the development of a leg on the head instead of a antennae,
 * in humans, HOX1 mutation causes craniosynostosis.

Pair-rule genes (PAX)

 * They also contain a homeodomain (homeobox)
 * They specify the nature of the segments,
 * regulated by gap genes,
 * expressed in 7 stripes along the anterioposterior axis,
 * they divide the embryo into 15 parasegments,
 * their mutations reduce the number of segments by half (fushi tarazu - development of odd parasegments, even-skipped - development of even parasegments),
 * PAX3 mutation = Waardenburg syndrome (deafness, white strand of hair, iris heterochromia).

(Para)segment polarity genes

 * They influence the anterioposterior polarity of parasegments, defined by pair-rule genes,
 * the embryo is gradually divided into smaller and smaller developmental sections,
 * e.g. engrailed gen.

Tissue-specific genes

 * A cascade of hundreds of genes,
 * eyeless gene - its mutation in Drosophila causes the development of a rudimentary eye, in mice microophthalmia and in humans aniridia,
 * when the eyeless gene is linked to the promoter of a gene typical for another tissue, an eye develops in this tissue,
 * with interspecies transfer of the eyeless gene, a species-specific eye is created → basic tissue-specific genes are developmentally old,
 * other, developmentally younger and species-specific genes also decide on the definitive form of the organ.

The spectrum of genes that is expressed in a certain type of cells is determined by RNA - DNA saturation.