Hox Genes

Hox Genes in the Spinal Cord What do the following regions contain? 1) Cervical region 2) Brachial + lumbar regions

1) Phrenic motor column 2) Lateral motor column

Hox genes in the vertebral column All mammals have what

7 cervical vertebrae

Hox Genes What are Hox genes?

A homeobox gene - Hox gene - is a gene that has within it a conserved region that codes for the amino acids that will make up the homeodomain.

Hox Genes What do Hox genes confer?

AP identity in all animals

Hox Genes in the CNS What happens in HoxB1 mutants?

Affects r4 specific specific neurones: - Facial Branchial motor neurons - Vestibular acoustic motor neruons

Hox genes in the vertebral column Removing Hox gene function from eh vertebrae has what effect?

Anteriorising - gain features of anterior vertebrae

Hox Genes What is a prologue?

Genes related by duplication within a genome such as HoxA1 and HoxB1.

Hox Genes in the CNS Where are Hox genes expressed in the CNS

Hox 1 to 5 are expressed in the hind brain, while Hox 4-11 is expressed in the spinal cord. There is no Hox gene expression in the forebrain or midbrain.

Hox genes in the vertebral column What Hox gene has rib forming abilities?

Hox 6 - overexpression of Hox6 causes ectopic rib formation while blocking it prevents rib formation. Hox6 is needed for normal rib development in the thoracic region

Essay Subtitles

Hox Genes Hox in CNS Hox in Spinal cord Hox in vertebral column

Hox genes in the vertebral column What Hox gene has rib blocking abilities?

Hox10 - you lose Hox10 lumbar segments become anteriorised and start making ribs, overexpression of Hox10 causes blocking of rib formation

Hox genes in the vertebral column Give an example of an anterior mutant?

HoxB4-/- or HoxD4-/- C2 gains anterior arch of atlas structure as well as maintaining its dens protrusion

Hox Genes When were Hox genes first genetically identified?

In Drosophila

Hox Genes How many clusters of Hox genes do mammals have?

Mammals have 4 clusters of Hox genes: a-b-c-d, each on a different chromosome, genes numbered 1 to 13

Hox Genes in the Spinal Cord Different Hox gene expression does what?

Maps out different spinal territories

Hox Genes in the CNS What has retrograde tracing revealed?

Motor neurons develop within the confines of pairs of rhombomeres. Trigeminal nerve: r2 + r3 Facial nerve: r4 + r5 Glossopharyngeal nerve: r6 + r7.

Hox Genes in the Spinal Cord A HoxC9 mutation results in what?

Mutants lacking PCG, HMC (+MMC) and instead the cells and transformed into lateral motor column (LMC) as Hoxc6 expressed in the brachial region extends laterally.

Hox Genes in the Spinal Cord Describe the thoracic segment of the spinal cord in relation to Hox gene expression

Only HoxC9 expressed that regulates: - Preganglionic motor column - Hypaxial motor column - Medial motto column

Hox Genes in the CNS Describe the hindbrain

Overtly segmented structure which is subdivided into 8 rhombomeres (r1 to r8), these rhombomeres are the plan on which the development of the hind brain is built.

Hox Genes What are Hox genes important for?

Patterning of the CNS, vertebral column and the limbs

Hox Genes in the CNS Motor nerves from the rhombomeres head where?

Pharyngeal arches, the trigeminal nerve to PA1, facial nerve to PA2 and glossopharyngeal nerve to PA3.

Hox Genes in the CNS What provides the retinoic acid gradient?

RALDH2 posteriorly which is a synthetic enzyme of RA, and Cyp26C1 which is a RA degradative enzyme expressed in the anterior mesoderm.

Hox Genes in the CNS What limits Hox gene expression

Retinoic acid - High concentrations of retinoic acid generate posterior rhombomeres, while low concentrations generate anterior rhombomeres.

Hox Genes What is an orthologue?

Same gene in a different species e.g. HoxA1 in mice and HOXA1 in humans

Hox genes in the vertebral column The anterior boundaries of Hox gene expression correspond to what?

Somite boundaries

Hox Genes in the CNS Describe Hox gene expression in the rhombomeres

The different rhombomeres express different concentrations of Hox, Hox genes are expressed from posterior to a defined anterior limit. Further posterior you go the more Hox genes that are expressed HoxA2 --> R1/R2 HoxB4 --> R6/R7 HoxB1 --> R4 only

Hox Genes What is an effect of paralogues?

There is a possibility for redundancy (genes can substitute for each other)

Hox Genes in the CNS What happens in HoxA2 mutants

r2 and r3 development is altered as you get a loss of trigeminal neurons, instead many neurons from r2 and r3 begin to contribute to the facial nerve as they become confused to what they should be doing