A novel cis-regulatory element drives early expression of Nkx3.2 in the gnathostome primary jaw joint

Abstract

The acquisition of movable jaws was a major event during vertebrate evolution. The role of NK3 homeobox 2 (Nkx3.2) transcription factor in patterning the primary jaw joint of gnathostomes (jawed vertebrates) is well known, however knowledge about its regulatory mechanism is lacking. In this study, we report a proximal enhancer element of Nkx3.2 that is deeply conserved in most gnathostomes but undetectable in the jawless hagfish and lamprey. This enhancer is active in the developing jaw joint region of the zebrafish Danio rerio, and was thus designated as jaw joint regulatory sequence 1 (JRS1). We further show that JRS1 enhancer sequences from a range of gnathostome species, including a chondrichthyan and mammals, have the same activity in the jaw joint as the native zebrafish enhancer, indicating a high degree of functional conservation despite the divergence of cartilaginous and bony fish lineages or the transition of the primary jaw joint into the middle ear of mammals. Finally, we show that deletion of JRS1 from the zebrafish genome using CRISPR/Cas9 results in a significant reduction of early gene expression of nkx3.2 and leads to a transient jaw joint deformation and partial fusion. Emergence of this Nkx3.2 enhancer in early gnathostomes may have contributed to the origin and shaping of the articulating surfaces of vertebrate jaws.

Enhanced contrast synchrotron X-ray microtomography for describing skeleton-associated soft tissue defects in zebrafish mutants

“…Our histopathological findings in bone-associated soft tissues obtained by applying DICE-PPC-SRµCT demonstrates a great potential of this technique for the investigation of small fish skeletal disease models involving gene mutants and regulatory sequence mutants that often display subtle phenotypes ( 66 ), and also for skeleton-associated regeneration experiments and general developmental studies of, for example, mineralization progression. For some questions, particularly those involving adult fish and large soft tissues, conventional µCT combined with contrasting agents may be sufficient, as has been already shown for mouse ( 67 ) and in a limited number of zebrafish studies (e.g.…”

Gene regulatory dynamics during the development of a paleopteran insect, the mayflyCloeon dipterum

“…This diversity of forms and lifestyles is the result of changes in the gene regulatory networks (GRNs) controlling the embryonic and postembryonic development of this clade (Carroll 1998; Molina-Gil et al 2023). In recent decades, the importance of regulatory information responsible for the location and time in which genes and GRNs are functioning, has been widely recognised (Furlong and Levine 2018; Leyhr et al 2022; Gompel et al 2005; Andrikou and Arnone 2015). These so called cis regulatory elements (CREs) are major players of morphological evolution not only in insects, but also in other animal lineages (Guerreiro et al 2013; Leyhr et al 2022).…”

“…In recent decades, the importance of regulatory information responsible for the location and time in which genes and GRNs are functioning, has been widely recognised (Furlong and Levine 2018; Leyhr et al 2022; Gompel et al 2005; Andrikou and Arnone 2015). These so called cis regulatory elements (CREs) are major players of morphological evolution not only in insects, but also in other animal lineages (Guerreiro et al 2013; Leyhr et al 2022). Still, some changes in trans, - in the coding sequences of transcription factors (TFs) and/or signalling molecules-have been also shown to participate in the diversity of phenotypes observed in animals (Galant and Carroll 2002; Santos et al 2017).…”

How vertebrates got their bite

“…Very few enhancer sequences have been preserved between species over long evolutionary periods ( Long et al, 2016 ), and these often control processes related to development ( Pennacchio et al, 2006 ; Bejerano et al, 2004 ; Lettice et al, 2003 ; Kvon et al, 2016 ; Leal and Cohn, 2016 ; Letelier et al, 2018 ). Now, in eLife, Tatjana Haitina and colleagues from Uppsala University – including Jake Leyhr as first author – report the discovery of a widely conserved enhancer named Joint Regulatory Sequence 1 (JRS1) that is critical for the development of the jaw joint and, potentially, the early evolution of the jaw ( Leyhr et al, 2022 ).…”