The key difference between homeobox and hox genes is that homeobox genes are mainly involved in the regulation of the entire morphogenesis process, while hox genes are a subset of homeobox genes which only regulate the formation of axes and appendages in organisms.
Regulation of structural development is an important process during embryonic development. Homeobox genes and hox genes play an important role in the whole process by acting as transcription factors that enhance the gene expression of the respective genes. These genes are highly conserved, and mutations to these genes can have many adverse effects.
CONTENTS
1. Overview and Key Difference
2. What are Homeobox Genes
3. What are Hox Genes
4. Similarities Between Homeobox and Hox Genes
5. Side by Side Comparison – Homeobox vs Hox Genes in Tabular Form
6. Summary
What are Homeobox Genes?
There are many anatomical changes that take place in organisms during their lifecycle. This phenomenon is known as morphogenesis. The genes responsible for regulating these anatomical changes are called homeobox genes. These consist of a DNA sequence that is about 180 base pairs long. They are preliminary found in animals, plants, fungi and other eukaryotic organisms.
The expression of homeobox genes gives rise to homeodomain proteins. These homeodomain proteins are mostly transcription factors. They aid in the folding process of DNA and accessory proteins during the genetic expression, thus regulating the whole expression process. Therefore, homeobox genes play an important role in the regulation process. However, a mutation in the homeobox genes may cause great damage to the regulatory processes.
Figure 01: Homeodomain
The homeobox domains were first identified in Drosophila and are highly conserved regions in the genome of vertebrates. The characteristic homeodomain gives rise to a protein with 60 amino acids forming alpha-helix secondary structures. The activity of these regulatory proteins coded by homeobox genes is most evident during the early embryonic phase, where the formation of body axes takes place. It also induces cellular differentiation in eukaryotes. There are two types of homeobox genes. They are – POU genes and HOX genes.
What are Hox Genes?
Hox genes form a subset of the homeobox genes. They are specifically related to the regulation of the body plan development during the embryonic stage of the life cycle. The proteins encoded by hox genes regulate the position and the accurate structuring of the body plan. This includes the placement of legs, appendages such as antennae and wings in most eukaryotic animals.
Vertebrates have special hox genes that regulate the positioning of the individual vertebrae in the vertebral column. Hox genes also regulate the segmentation of the body of higher organisms.
Figure 02: Hox Genes
Coinciding with homeobox genes, hox genes also encode for transcription factors. They are also conserved regions. At present, around 39 Hox genes have been identified. Hox genes also code for proteins that form secondary alpha-helices, which enable them to entangle during transcription of genes to upregulate the process.
As hox genes play a major role in the early development of the animal body, mutations in these genes can lead to fatal effects or abnormalities of body structure development. Thus, these genes play a major role in maintaining body posture and structure.
What are the Similarities Between Homeobox and Hox Genes?
- Homeobox and hox genes are present in eukaryotes.
- Both are important in early embryonic development.
- They are highly conserved regions in the genome.
- Both give rise to various transcription factors that regulate transcription.
- Moreover, they give rise to proteins that comprise secondary alpha structures.
- Mutations taking place in both genes can lead to abnormal expression of body structure.
- Both genes are mainly involved in the morphogenesis of higher organisms.
What is the Difference Between Homeobox and Hox Genes?
The key difference between homeobox and hox genes is the scope of its function. While homeobox genes regulate the entire anatomical morphogenesis process, hox genes only regulate the axes development and the development of structural appendages during the morphogenesis. The number of homeobox genes and the hox genes also vary. There are around 200 homeobox genes while there are around 39 hox gens.
The below infographic summarizes the difference between homeobox and hox genes.
Summary – Homeobox vs Hox Genes
Homeobox genes and hox genes are highly conserved genes. They are the main genes involved in the regulation of anatomical development of higher-level organisms, including vertebrates. While homeobox genes are a large group of genes, hox genes are a subset of homeobox genes. Therefore, hox genes specifically regulate the development of axes and appendages, while homeobox genes generally regulate the entire structural morphogenesis. Both genes code for transcription factors that enhance and regulate the process. Mutations in both genes can have many disadvantageous outcomes. So, this is the summary of the difference between homeobox and hox genes.
Reference:
1. “Homeotic Genes and Body Patterns.” Learn Genetics, Available here.
Image Courtesy:
1. “Homeodomain-dna-1ahd” By Opabinia regalis – Self created from PDB entry 1AHD using the freely available visualization and analysis package VMD (CC BY-SA 3.0) via Commons Wikimedia
2. “Hox-genes-drosophila” By Antonio Quesada Díaz – Template:Wiki commons modified (Public Domain) via Commons Wikimedia