Analysis of NUAK1 and NUAK2 expression during early chick development reveals specific patterns in the developing head

Abstract

Several human diseases are associated with the NUAK1 and NUAK2 genes. These genes encode kinases, members of the AMPK-related kinases (ARK) gene family. Both NUAK1 and NUAK2 are known targets of the serine threonine kinase LKB1, a tumor suppressor involved in regulating cell polarity. While much is known about their functions in disease, their expression pattern in normal development has not been extensively studied. Here, we present the expression patterns for NUAK1 and NUAK2 in the chick during early-stage embryogenesis, until day 3 (Hamburger and Hamilton stage HH20). Several embryonic structures, in particular the nascent head, showed distinct expression levels. NUAK1 expression was first detected at stage HH6 in the rostral neural folds. It was then expressed (HH7-11) throughout the encephalalon, predominantly in the telencephalon and mesencephalon. NUAK1 expression was also detected in the splanchnic endoderm area at HH8-10, and in the vitellin vein derived from this area, but not in the heart. NUAK2 expression was first detected at stage HH6 in the neural folds. It was then found throughout the encephalon at stage HH20. Particular attention was paid in this study to the dorsal ectoderm at stages HH7 and HH8, where a local deficit or accumulation of NUAK2 mRNA were found to correlate with the direction of curvature of the neural plate. This is the first description of NUAK1 and NUAK2 expression patterns in the chick during early development; it reveals non-identical expression profiles for both genes in neural development. KEY WORDS: NUAK, chick embryo, in situ hybridizationNUAK1 and NUAK2 are members of the novel (Nua) kinases family. Their alternative names include: ARK5 or OMPHK1 for NUAK1; and SNARK or OMPHK2 for NUAK2. They are two of the fourteen known substrates of the serine threonine kinase LKB1 and are part of the AMPK-related protein kinase family (ARK) (Al-Hakim et al., 2005, Hardie and Alessi, 2013, Manning et al., 2002, Suzuki et al., 2003. AMPK is a mammalian homolog of sucrose non-fermentable protein kinase (SNF-1); it is a member of a serine/threonine protein kinase family. Unlike AMPK, which is activated under various stress conditions resulting in decreased ATP concentrations (Scott et al., 2007), ARKs do not have AMP: ATP ratio-sensitive regulatory subunits. Thus, they do not directly participate in adaptive responses to energy balance (Al-Hakim et al., 2005).NUAK1 was first described as supporting AKT-dependent cell survival during nutrient starvation (Suzuki et al., 2003), and has been shown to induce p53 phosphorylation (Hou et al., 2011). NUAK1 expression is now known to be closely associated with metastases, colorectal cancer and is an indicator of poor prognoInt. J. Dev. Biol. 58: 379-384 (2014) sis for glioma (Lu et al., 2013). Recently, it was shown to favor an invasive phenotype in human breast cancer which also depended on AKT signaling. This may be linked to its role in cell adhesion through phosphorylation of the regulatory sub-unit of the myosin light chain 2 (MLC...

A loss-of-function NUAK2 mutation in humans causes anencephaly due to impaired Hippo-YAP signaling

“…NUAK2 encodes an SNF1/AMPK-related kinase (also known as SNARK), which is often amplified in human cancers ( Namiki et al, 2011 ; Sun et al, 2013 ). In animal studies, it was shown that Nuak2 is specifically expressed in neural folds of the nascent head of chick and mouse embryos ( Bekri et al, 2014 ; Hirano et al, 2006 ; Ohmura et al, 2012 ). Local deficit or accumulation of Nuak2 mRNA in chick neural folds correlated with the curvature direction of the neuroectoderm at the median hinge point and dorsolateral hinge point ( Bekri et al, 2014 ).…”

“…In animal studies, it was shown that Nuak2 is specifically expressed in neural folds of the nascent head of chick and mouse embryos ( Bekri et al, 2014 ; Hirano et al, 2006 ; Ohmura et al, 2012 ). Local deficit or accumulation of Nuak2 mRNA in chick neural folds correlated with the curvature direction of the neuroectoderm at the median hinge point and dorsolateral hinge point ( Bekri et al, 2014 ). Importantly, Nuak2 knockout mice show NTDs including exencephaly in 40% of live births, which lends strong support for a potential role for this kinase during NTC in mammals ( Ohmura et al, 2012 ).…”

Glycine Promotes the Survival of a Subpopulation of Neural Stem Cells

“…The embryos were then hydrated by inverted gradients and loaded into sample holders and mounted into an in situ hybridization device (Folgentec-France). Embryos were subjected for 22 h to a continuous stream (1.7 ml/min) of successive reagents following the in situ hybridization protocol as previously described (Bekri et al, 2014 ). Finally, enzymatic detection was performed in PM purple reagent (Roche) under constant observation.…”

Defining the Neural Kinome: Strategies and Opportunities for Small Molecule Drug Discovery to Target Neurodegenerative Diseases

“…This kinase is highly expressed early in the developing brain and in microglia (Figure 3). 79 NUAK1 was reported as a biomarker for AD in a GWAS (Table 1). Through assessment of Aβ levels in vivo via PET imaging, NUAK1 was associated with quantitative global Aβ loading.…”