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The regulation of erythropoiesis by Hedgehog (Hh) signalling

Norris, S; (2017) The regulation of erythropoiesis by Hedgehog (Hh) signalling. Doctoral thesis , UCL (University College London).

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Abstract

Dhh (Desert Hedgehog) is one of three Hedgehog (Hh) proteins essential for testis development and Schwann cell function. Gli1, Gli2, and Gli3 are dedicated transcription factors that transduce the Hh pathway. A study published by our group showed significant changes in erythrocyte differentiation in Dhh-deficient mice, under steady state and stress-induced conditions, implicating Dhh as a negative regulator of murine erythropoiesis (Lau et al., 2012). To investigate these phenotypic differences, we created an mCherry reporter mouse line for Dhh using Bacterial Artificial Chromosome ‘recombineering’ and hypothesised that Dhh is produced by the splenic stroma, especially red pulp fibroblasts (RPFs), under steady state and anaemic stress. Erythroblast kinetics were also analysed in Hedgehog-related mouse lines during haematopoietic recovery. After validating the mCherry line as a faithful reporter of Dhh using testes, brain and thymic tissue, we found that Dhh (mCherry) is expressed by a fraction of all splenic ICAM-1+ stromal cells in particular RPFs and also fibroblast reticular cells (FRCs), disproving our steady state hypothesis. During anaemia, Dhh was not upregulated but showed most expression in the RPF subset in support of our hypothesis, while some follicular dendritic cells (FDCs) and marginal reticular cells (MRCs) significantly upregulated Dhh. Interestingly, Dhh was more highly detected in antigen-presenting cells (APCs) and some non-APCs under normal and anaemic conditions, potentially implicating Dhh in white pulp splenic functions. Irradiating Dhh-deficient mice corroborated Dhh as a negative erythropoietic regulator by analysing reticulocytes and splenic erythroid progenitors, in line with Dhh-deficient mice exhibiting less Gli-binding activity in their BM and spleen. In Gli3-heterozygote mice elevated Shh but reduced Dhh expression was found in the spleen, supporting our hypothesis that Gli3 represses Shh. Irradiating Gli3-heterozygote mice showed significant expansion of erythroblast differentiation in the BM but not the spleen, highlighting the intricacies of the Hh signalling pathway in erythropoiesis.

Type: Thesis (Doctoral)
Title: The regulation of erythropoiesis by Hedgehog (Hh) signalling
Event: University College London
Language: English
UCL classification: UCL > School of Life and Medical Sciences
UCL > School of Life and Medical Sciences > Faculty of Life Sciences
URI: http://discovery.ucl.ac.uk/id/eprint/1537627
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