Ssrp1a controls organogenesis by promoting cell cycle progression and RNA synthesis

Abstract

SUMMARYTightly controlled DNA replication and RNA transcription are essential for differentiation and tissue growth in multicellular organisms. Histone chaperones, including the FACT (facilitates chromatin transcription) complex, are central for these processes and act by mediating DNA access through nucleosome reorganisation. However, their roles in vertebrate organogenesis are poorly understood. Here, we report the identification of zebrafish mutants for the gene encoding Structure specific recognition protein 1a (Ssrp1a), which, together with Spt16, forms the FACT heterodimer. Focussing on the liver and eye, we show that zygotic Ssrp1a is essential for proliferation and differentiation during organogenesis. Specifically, gene expression indicative of progressive organ differentiation is disrupted and RNA transcription is globally reduced. Ssrp1a-deficient embryos exhibit DNA synthesis defects and prolonged S phase, uncovering a role distinct from that of Spt16, which promotes G 1 phase progression. Gene deletion/replacement experiments in Drosophila show that Ssrp1b, Ssrp1a and N-terminal Ssrp1a, equivalent to the yeast homologue Pob3, can substitute Drosophila Ssrp function. These data suggest that (1) Ssrp1b does not compensate for Ssrp1a loss in the zebrafish embryo, probably owing to insufficient expression levels, and (2) despite fundamental structural differences, the mechanisms mediating DNA accessibility by FACT are conserved between yeast and metazoans. We propose that the essential functions of Ssrp1a in DNA replication and gene transcription, together with its dynamic spatiotemporal expression, ensure organ-specific differentiation and proportional growth, which are crucial for the forming embryo.

A large-scale in vivo RNAi screen to identify genes involved in Notch-mediated follicle cell differentiation and cell cycle switches

“…Ssrp shows nucleosomal DNA binding ability 39 40 , indicating that it could be a critical component of chromatin remodeling complexes regulating Notch signaling. Our finding that Ssrp regulates epithelial follicle cell differentiation and cell cycle transition during Drosophila oogenesis is consistent with a previous report showing that Ssrp1a, the zebrafish Ssrp homolog, controls development of tissues like the liver and eye by promoting cell proliferation and differentiation 41 . mop is a very interesting gene, encoding a protein-tyrosine phosphatase that contains BRO1 domain and ALIX V-shaped domain.…”

SSRP1 Cooperates with PARP and XRCC1 to Facilitate Single-Strand DNA Break Repair by Chromatin Priming

“…FACT is highly expressed in undifferentiated cells, and its deficiency leads to zebrafish developmental defects (47) and mouse embryo lethality (48). Interestingly, FACT is frequently upregulated in undifferentiated aggressive tumors, indicating a potential role as an anti-cancer target (49–51).…”

A Novel Zebrafish ret Heterozygous Model of Hirschsprung Disease Identifies a Functional Role for mapk10 as a Modifier of Enteric Nervous System Phenotype Severity

“…Embryos were incubated with BrdU for 30 minutes, essentially as described [64] and processed for immunostaining, as above, except embryos were reared in PTU, and following fixation, dehydrated in methanol, rehydrated, washed in PBT, digested in 10mg/ml proteinase K for 10 minutes, washed in PBT, and post-fixed in 4%PFA for 20 minutes. Embryos were then washed in water, equilibrated in 2N HCl, before denaturing for 1 hour in 2N HCl at room temperature, neutralizing with two 10 minute 0.1M sodium tetraborate washes, and washing in PBT before blocking and immunostaining as above.…”