Abstract
In the fly Drosophila melanogaster, a hierarchic segmentation gene cascade patterns the anterior-posterior body axis of the developing embryo. Within this cascade, the pair-rule genes (PRGs) transform the more uniform patterning of the higher-level genes into a metameric pattern that first represents double-segmental units, and then, in a second step, represents a true segmental pattern. Within the PRG network, primary PRGs regulate secondary PRGs that are directly involved in the regulation of the next lower level, the segment-polarity genes (SPGs). While the complement of primary PRGs is different in Drosophila and the beetle Tribolium, another arthropod model organism, both paired (prd) and sloppy-paired (slp), acts as secondary PRGs. In earlier studies, the interaction of PRGs and the role of the single slp ortholog in Tribolium have been investigated in some detail revealing conserved and diverged aspects of PRG function. In this study, I present the identification and the analysis of embryonic expression patterns of a second slp gene (called slp2) in Tribolium. While the previously identified gene, slp, is expressed in a typical PRG pattern, expression of slp2 is more similar to that of the downstream-acting SPGs, and shows expression similarities to slp2 in Drosophila. The previously reported differences between the function of slp in Drosophila and Tribolium may partially account for the function of the newly identified second slp paralog in Tribolium, and it may therefore be advised to conduct further studies on PRG function in the beetle.
Highlights
In the dipteran fly Drosophila melanogaster, a hierarchic segmentation gene cascade almost synchronously controls the patterning of the early embryo along the anterior-posterior (AP) body axis into a defined number of single segments
While it is still unclear if pair-rule patterning is a conserved ancestral trait of arthropod segmentation, it appears likely that the pair-rule genes (PRGs) in general are involved in segmentation, as evident from functional studies (e.g. Liu and Kaufman 2005; Mito et al 2007; Rosenberg et al 2015; Xiang et al 2017; Auman and Chipman 2018), and the analysis of gene expression patterns (e.g. Damen et al 2000, 2005; Dearden et al 2002; Hughes and Kaufman 2002; Chipman and Akam 2008; Janssen et al 2011; Green and Akam 2013; Schönauer et al 2016)
Tribolium Slp clusters with high confidence with Drosophila Sloppypaired1 (Slp1), and it seems clear that those two form an orthology-pair
Summary
In the dipteran fly Drosophila melanogaster, a hierarchic segmentation gene cascade almost synchronously controls the patterning of the early embryo along the anterior-posterior (AP) body axis into a defined number of single segments (reviewed in e.g. Akam 1987, Davis and Patel 2003). Single segmental units are added from the SAZ (e.g. Hughes and Kaufman 2002; Schoppmeier and Damen 2005; Janssen et al 2011), but in some arthropods, all, or a number of segments, are added (or patterned) with a double-segment periodicity (e.g. Binner and Sander 1997; Dearden et al 2002; Chipman et al 2004; Erezyilmaz et al 2009; Janssen et al 2012; El-Sherif et al 2012; Sarrazin et al 2012). This latter mechanism is reminiscent of the initial expression of the PRGs in Drosophila and their pair-rule function. While it is still unclear if pair-rule patterning (and function) is a conserved ancestral trait of arthropod segmentation, it appears likely that the PRGs in general are involved in segmentation, as evident from functional studies (e.g. Liu and Kaufman 2005; Mito et al 2007; Rosenberg et al 2015; Xiang et al 2017; Auman and Chipman 2018), and the analysis of gene expression patterns (e.g. Damen et al 2000, 2005; Dearden et al 2002; Hughes and Kaufman 2002; Chipman and Akam 2008; Janssen et al 2011; Green and Akam 2013; Schönauer et al 2016)
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