SOX2: Functional analysis using mouse mutants

McIntyre Bell, Donald (2005). SOX2: Functional analysis using mouse mutants. PhD thesis The Open University.



The Sox genes are a large group of transcription factors with representatives in all animal species and initial investigations have demonstrated the importance of many members of this family during embryogenesis.

The expression pattern of Sox2 was surveyed in the second half of gestation by examining the X-gal staining pattern of Sox2Bgeo-/+ embryos in wholemount and section immunohistochemistry using a SOX2 specific polyclonal antibody. Particular attention was given to the pattern in the developing inner ear and in the hair follicle. Expression suggests that Sox2 plays significant roles in a diverse range of tissues throughout embryogenesis.

The null mutation of Sox2 demonstrates a critical requirement for this gene in embryogenesis but early lethality of Sox2Bgeo-/+ embryos precludes study at later stages. A strategy to produce a conditionally null allele of Sox2 was devised to circumvent the early lethality and allow functional investigation of Sox2 in a tissue specific and/or time dependent manner throughout embryogenesis and post-natally. Initial attempts to target the Sox2 allele were unsuccessful but redesigning the targeting vector resulted in the production of correctly targeted ES cells. Targeted clones were used to produce high percentage chimeras but the ES cell component did not contribute to subsequent generations.

Two mouse mutants, Lcc and Ysb display abnormalities in inner ear and coat formation. Expression analysis and physical mapping implicate Sox2 as a strong candidate affected by these alleles. The creation of mice carrying combinations of Sox2Bgeo-/+, Lcc and Ysb mutations showed that they are allelic and that inner ear and coat abnormalities are caused predominantly by the loss of expression of Sox2. Congenic breeding of Sox2Bgeo-/+ mice onto a C3H/He background revealed heterozygous coat phenotypes confirming an important role for Sox2 in hair formation.

The closely related gene Sox1 is co-expressed along with Sox2 during CNS development and physical similarities between their protein products suggest overlapping functions able to compensate for the loss of either gene. Breeding experiments demonstrate an increase in the rate of mortality far greater than that expected by the addition of individual phenotypes. Immunohistochemical analysis reveals aberrant cell behaviour in CNS progenitor cell populations carrying the most severe genotype and suggests some common function between these genes during CNS development.

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