Abrogation of Stem Loop Binding Protein (Slbp) function leads to a failure of cells to transition from proliferation to differentiation, retinal coloboma and midline axon guidance deficits

Abstract

Through forward genetic screening for mutations affecting visual system development, we identified prominent coloboma and cell-autonomous retinal neuron differentiation, lamination and retinal axon projection defects in eisspalte (ele) mutant zebrafish. Additional axonal deficits were present, most notably at midline axon commissures. Genetic mapping and cloning of the ele mutation showed that the affected gene is slbp, which encodes a conserved RNA stem-loop binding protein involved in replication dependent histone mRNA metabolism. Cells throughout the central nervous system remained in the cell cycle in ele mutant embryos at stages when, and locations where, post-mitotic cells have differentiated in wild-type siblings. Indeed, RNAseq analysis showed down-regulation of many genes associated with neuronal differentiation. This was coincident with changes in the levels and spatial localisation of expression of various genes implicated, for instance, in axon guidance, that likely underlie specific ele phenotypes. These results suggest that many of the cell and tissue specific phenotypes in ele mutant embryos are secondary to altered expression of modules of developmental regulatory genes that characterise, or promote transitions in, cell state and require the correct function of Slbp-dependent histone and chromatin regulatory genes.Congenital deficits of eye formation are common in humans and to help understand the genetic basic of such conditions, we are studying zebrafish with comparable eye defects. We identified defects in both the shaping of the eye and in its connections to the brain in eisspalte mutant fish. Further analyses revealed additional deficits in the brain, most notably a severe reduction in neurons and their connections. We find that this is due to an inability of the cells that generate neurons to transition from proliferation to neuronal differentiation. By using a sequencing approach to compare mutant embryos to their normal siblings, we identified the affected gene as slbp, which encodes a protein that binds the mRNAs of other genes important for cell proliferation. This sequencing approach revealed the full extent of changes in gene expression in the mutant, helping us to better understand why the nervous system defects occur. Our study suggests that in the absence of Slbp function, cells lose the ability to transition from the proliferative to the differentiated state and this leads to additional defects in the eyes and brain.

Tissue-Specific Requirement for the GINS Complex During Zebrafish Development

“…Markers z7256 and z10008 flanked a ∼12.6 Mb interval containing 183 genes. Next generation sequencing, combined with a slightly modified version (Turner et al, 2019) of the Variant Discovery Mapping (VDM) CloudMap pipeline (Minevich et al, 2012) pipeline confirmed and refined this position. Instead of plotting individual allele frequencies, the kernel density of homozygous/heterozygous SNPs was plotted along each chromosome.…”

Identification ofSlit3as a locus affecting nicotine preference in zebrafish and human smoking behaviour

“…Therefore we performed immunostaining of the axonal projections in three-day-190 old zebrafish larvae and looked at the expression patterns along the midline in the 191 ventral forebrain, where Slit3 is known to be expressed (32). No differences between 192 Slbp ty77e/ty77e were used as positive control for antibody staining, as these mutants have 208 fewer neurons and show axonal defects (33). n=10 samples per genotype group.…”

Nf2 fine-tunes proliferation and tissue alignment during closure of the optic fissure in the embryonic mouse eye

“…In humans, a subpopulation of colobomata is a result of mutations in developmentally important genes, however, the origins for many OF closure defects are unknown (for reviews, see (3,7,8,13,14)). Additional genes have been identified in animal models; substantial progress has been made in understanding critical processes, including growth and patterning of the ventral optic cup and optic nerve head (15- 19), cell-cell contact and signaling (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), crosstalk with migrating hyaloid precursors and extracellular matrix components (31)(32)(33)(34)(35)(36), cytoskeleton dynamics (37,38), epigenetics (39), degradation of ECM and cellular proteins (40)(41)(42), programmed cell death, survival and cell proliferation (43,44) (for reviews, see (7,8,13)). Elegant in vivo imaging studies in zebrafish and excellent anatomical analyses in chick have characterized important morphogenetic and cellular behavior (20,27,34,(45)(46)(47)(48)(49).…”