Hox Genes

How were hox genes identified?

1. Architectural plans of the developing fly embryo were being researched. 2. They found there were clusters of genes which turn on in sequence which determined the overall body pattern. 3. The Homeobox was most important to this.

When were hox genes first identified?

1970s

What does the Homeobox encode?

60bp sequence called the homeodomain.

Homeosis defined by?

Bateson in 1894

Hox gene expression in Drosophila

Controlled by 4 families 1. Extra sex combs (esc) 2. Polycomb (pc) 3. Super sex combs (sxc) 4. Trithorax (trx)

Distalless gene in drosophila

Forms the head.

What do hox genes act like?

Genetic switches that turn on and off other genes. So control the timing and route of development.

Ubx gene in drosophila

Represses distalless. Its transcription is localised to the anterior-posterior axis and functions in the T3 segment to distinguish that segment from T2.

Hox gene expression

exhibits colinearity

How many hox genes do humans have?

39, in 4 clusters.

Job of the 60bp protein?

A DNA binding domain which tells cells in various segments of a developing embryo what kind of structures to make.

Homeotic Mutant

A mutant with an affected segment of the same structure as that belonging to a neighbouring structure (e.g. leg on the head instead of an antennae).

Drosophila clusters

ANT-C (antennapedic, the head and the first 2 thoracic segments) BX-C (Bithorax, posterior of the 2nd thoracic segment and the 3rd thoracic segment and abdominal segment)

Hox protein use in humans:

Bone Morphogenetic Protein 4 (BMP4) and Chordin are involved in specifying the identity of cells along the dorso-ventral axis of the developing neurotube.

Hox genes

Control the polarity of the embryo and the formation of the anterior-posterior body axis of many animals. (i.e. head to tail formation)

How does the homeotic complex work in vertebrates?

Governs overt and non-overt segmentation.

Hox and disorders:

HOXD13 mutants cause synpolydactyly (SPD) and other HOXD gene mutants relate to limb malformation.

A way of researching these genes?

Induced mutagenesis.

Highly conserved

Maintained by evolution despite speciation, so they must be very important.

Polycomb family

Their proteins control expression of Hox genes by altering chromatin conformation, thus blocking the binding of the transcription factor.

Action of the transcription factors

To cause segmental differences in development.

Homologous

To originate from a common ancestor.

The transcription factor includes?

a 180bp binding domain called the Homeobox.

Various actions of Hox genes?

helps with 1. Transcription 2. Translation 3. Cell signalling

Each hox gene encodes a?

protein which is a transcription factor.

Colinearity

their organisation on the chromosome reflects their expression in the body.