Hox-cluster genes in the spinocerebellar system

The Hox-cluster genes are a family of 39 transcription-factor genes and several micro (mi)RNAs, spread across four genomic clusters. These genes are known for their role in patterning along the anterior-posterior (A-P) axis in several vertebrate tissues, including the sensory circuitry of the hindbrain and motor neurons of the spinal cord. The discovery of expression of an eGFP reporter for the Hox miRNA miR-196a2 in neurons projecting to the cerebellum led to the hypothesis that the Hox genes may also play a role in patterning of the spinocerebellar system, which consists of anatomically independent nuclei, as well as scattered cell populations, specific to certain A-P levels of the spinal cord. This system also displays a complex, topographically arranged and genetically encoded projection to the cerebellar cortex, which is important for the coordination of motor output. Despite many years of anatomical study, genetic and molecular knowledge regarding the development of spinocerebellar neurons remains extremely sparse. The major aim of this thesis was to investigate the extent of Hox gene involvement in these neurons, and the potential that these genes may provide the positional identity to spinocerebellar neurons that must be required for their accurate incorporation into the local circuits of the cerebellum. This aim was pursued by detailed neuroanatomical investigations using a combination of in situ hybridisation techniques, neuronal tracing, and transgenic or knock-in fluorescent reporter genes. In the first section of the thesis, I analyse the expression of the miR-196a1-eGFP & miR-196a2-eGFP reporter genes across development in the cerebellum and spinal cord, and find the miR-196a2-eGFP reporter is broadly expressed across most spinocerebellar subpopulations, but displays a heterogeneity of expression both within and between subpopulations which may indicate a more complex molecular profile for these neurons. Additionally, this chapter highlights the usefulness of a broadly expressed spinocerebellar reporter for developmental investigations of this system.

Author requested conversion to open access 23 Jan 2024