Abstract
Loss of function mutations in granulin (GRN) are linked to two distinct neurological disorders, frontotemporal lobar degeneration (FTLD) and neuronal ceroid lipofuscinosis (NCL). It is so far unknown how a complete loss of GRN in NCL and partial loss of GRN in FTLD can result in such distinct diseases. In zebrafish, there are two GRN homologues, Granulin A (Grna) and Granulin B (Grnb). We have generated stable Grna and Grnb loss of function zebrafish mutants by zinc finger nuclease mediated genome editing. Surprisingly, the grna and grnb single and double mutants display neither spinal motor neuron axonopathies nor a reduced number of myogenic progenitor cells as previously reported for Grna and Grnb knock down embryos. Additionally, grna−/−;grnb−/− double mutants have no obvious FTLD- and NCL-related biochemical and neuropathological phenotypes. Taken together, the Grna and Grnb single and double knock out zebrafish lack any obvious morphological, pathological and biochemical phenotypes. Loss of zebrafish Grna and Grnb might therefore either be fully compensated or only become symptomatic upon additional challenge.
Highlights
Granulin (GRN) is a pleiotropic growth factor, which plays a role in wound healing, cancer, and inflammation [1]
At 24 hours post fertilization grna is most prominently expressed in the intermediate cell mass where precursors of blood and immune cells reside, consistent with the mammalian expression pattern [21], whereas grnb is predominantly expressed in various regions of the brain [14]
Among the four zebrafish granulins, grna and grnb were chosen for the generation of knock out (KO) mutants since they have a domain structure reminiscent of mammalian GRN. grna and grnb are both orthologous to human GRN with potentially redundant functions [14, 17]
Summary
Granulin (GRN) is a pleiotropic growth factor, which plays a role in wound healing, cancer, and inflammation [1]. Heterozygous loss of function mutations in GRN are linked to frontotemporal lobar degeneration (FTLD-TDP/GRN) [2, 3]. Two patients with neuronal ceroid lipofuscinosis (NCL) have been reported to be homozygous for loss of function mutations in GRN (NCL/GRN) [4]. FTLD-TDP/GRN patients present with extensive micro- and astrogliosis as well as TAR DNA binding protein 43 (TDP-43) and ubiquitin-positive intracellular inclusions [5,6,7]. Biochemical studies revealed that lysosomal proteins such as Cathepsin D (CTSD) are increased in brain samples from FTLD-TDP/GRN patients [5] suggesting lysosomal dysfunction upon loss of GRN. Skin biopsies of PLOS ONE | DOI:10.1371/journal.pone.0118956 March 18, 2015
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