The Enhancer of split transcription factor Her8a is a novel dimerisation partner for Her3 that controls anterior hindbrain neurogenesis in zebrafish

Abstract

BackgroundNeurogenesis control and the prevention of premature differentiation in the vertebrate embryo are crucial processes, allowing the formation of late-born cell types and ensuring the correct shape and cytoarchitecture of the brain. Members of the Hairy/Enhancer of Split (Hairy/E(spl)) family of bHLH-Orange transcription factors, such as zebrafish Her3, 5, 9 and 11, are implicated in the local inhibition of neurogenesis to maintain progenitor pools within the early neural plate. To better understand how these factors exert their inhibitory function, we aimed to isolate some of their functional interactors.ResultsWe used a yeast two-hybrid screen with Her5 as bait and recovered a novel zebrafish Hairy/E(spl) factor - Her8a. Using phylogenetic and synteny analyses, we demonstrate that her8a evolved from an ancient duplicate of Hes6 that was recently lost in the mammalian lineage. We show that her8a is expressed across the mid- and anterior hindbrain from the start of segmentation. Through knockdown and misexpression experiments, we demonstrate that Her8a is a negative regulator of neurogenesis and plays an essential role in generating progenitor pools within rhombomeres 2 and 4 - a role resembling that of Her3. Her8a co-purifies with Her3, suggesting that Her8a-Her3 heterodimers may be relevant in this domain of the neural plate, where both proteins are co-expressed. Finally, we demonstrate that her8a expression is independent of Notch signaling at the early neural plate stage but that SoxB factors play a role in its expression, linking patterning information to neurogenesis control. Overall, the regulation and function of Her8a differ strikingly from those of its closest relative in other vertebrates - the Hes6-like proteins.ConclusionsOur results characterize the phylogeny, expression and functional interactions involving a new Her factor, Her8a, and highlight the complex interplay of E(spl) proteins that generates the neurogenesis pattern of the zebrafish early neural plate.

A network of Notch-dependent and -independent her genes controls neural stem and progenitor cells in the zebrafish thalamic proliferation zone

“…her4 and her15, her6 and her9 , as well as her8a expression have been characterized in adult neural stem cell (NSC) zones (Chapouton et al, 2011; Zhou et al, 2012). Zebrafish homologs of Hes1 , Hes5 and Hes6 have also been investigated in the neural plate during early embryonic development (Bae et al, 2005; Takke et al, 1999; Webb et al, 2011). So far however, little is known about potential cross-regulatory interactions or redundancies among her genes in NSCs and during neurogenesis in larval neural proliferation zones.…”

HLH-29 regulates ovulation in C. elegans by targeting genes in the inositol triphosphate signaling pathway

“…Members of the Hairy-Enhancer of Split (HES) subfamily act primarily in response to Notch signaling (Fischer and Gessler, 2007; Kageyama et al, 2007), and are known for roles in neural (Kageyama et al, 2008; Li et al, 2008; Webb et al, 2011) and cardiovascular (Fischer et al, 2004; Xin et al, 2007; Wiese et al, 2010) development. In humans, mutations in the HES genes are often associated with neuroblastoma (Axelson, 2004; Stockhausen et al, 2005), neuroendocrine tumors of the breast, lung, and prostate (Hartman et al, 2009; Lu et al, 2010; Nasgashio et al, 2011), and early developmental disorders (Sparrow et al, 2008; Sparrow et al, 2010).…”

An Update on the Molecular Mechanism of the Vertebrate Isthmic Organizer Development in the Context of the Neuromeric Model

“…Studies using transgenic embryos carrying the recombined her5PAC:egfp construct have shown that the spatiotemporal dynamic expression of zebrafish her5 governs neurogenesis progression in a converging manner towards the MH constriction (Tallafuß and Bally-Cuif, 2003 ). During the growth and regionalization of the developing MH domain in zebrafish embryos, the bHLH Hairy/E(spl)-like factor Her5 accurately defines the “intervening zone” (IZ) as a neuron-free transverse stripe of delayed differentiation (Geling et al, 2003 , 2004 ; Tallafuß and Bally-Cuif, 2003 ), translating early positional information into accurate neurogenesis and cell proliferation in the developing MH domain in collaboration with other E(spl) factors in a dose-dependent manner (Sieger et al, 2004 ; Ninkovic et al, 2005 , 2008 ; Chapouton et al, 2006 ; Webb et al, 2011 ; Galant et al, 2016 ).…”