Abstract
Hox gene collinearity (HGC) is a multi-scalar property of many animal phyla particularly important in embryogenesis. It relates entities and events occurring in Hox clusters inside the chromosome DNA and in embryonic tissues. These two entities differ in linear size by more than four orders of magnitude. HGC is observed as spatial collinearity (SC), where the Hox genes are located in the order (Hox1, Hox2, Hox3 …) along the 3′ to 5′ direction of DNA in the genome and a corresponding sequence of ontogenetic units (E1, E2, E3, …) located along the Anterior—Posterior axis of the embryo. Expression of Hox1 occurs in E1, Hox2 in E2, Hox3 in E3, etc. Besides SC, a temporal collinearity (TC) has been also observed in many vertebrates. According to TC, first Hox1 is expressed in E1; later, Hox2 is expressed in E2, followed by Hox3 in E3, etc. Lately, doubt has been raised about whether TC really exists. A biophysical model (BM) was formulated and tested during the last 20 years. According to BM, physical forces are created which pull the Hox genes one after the other, driving them to a transcription factory domain where they are transcribed. The existing experimental data support this BM description. Symmetry is a physical–mathematical property of matter that was explored in depth by Noether who formulated a ground-breaking theory (NT) that applies to all sizes of matter. NT may be applied to biology in order to explain the origin of HGC in animals developing not only along the A/P axis, but also to animals with circular symmetry.
Highlights
Hox Gene Collinearity (HGC) is a basic embryonic property, coordinating the development of vertebrates and many other animal phyla
Lewis noticed that a class of Hox genes is located in clusters following an ordered sequence (Hox1, Hox2, Hox3, etc.) along the direction 30 to 50 on the chromosome (Figure 1)
In cooperation with this time-space-translation, temporal collinearity (TC) leads to the development of different body parts of the vertebrate embryo [7]
Summary
Hox Gene Collinearity (HGC) is a basic embryonic property, coordinating the development of vertebrates and many other animal phyla. It was first observed by E.B. Lewis in the Drosophila BX-C gene complex [1]. Lewis noticed that a class of Hox genes is located in clusters following an ordered sequence (Hox, Hox, Hox, etc.) along the direction 30 to 50 on the chromosome (Figure 1) These genes are expressed in the same order in the embryo along the anterior/posterior (A/P) axis. This is a general feature in Nature when phenomena at different ranges interact.
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