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    • We reveal that the four well known vertebrate families of

    2021-11-22

    We reveal that the four well known vertebrate families of KAT enzymes (GNAT, MYST, P300/CBP, Basal transcription factor/nuclear receptor co-activator) seem to be conserved (Karmodiya et al., 2014; Roth et al., 2001; Sheikh & Akhtar, 2018) in the mangrove rivulus, together with Camello, a potential novel class of acetyltransferase, recently characterized in Danio rerio (), and some other high confidence KAT members (ATAT1, Kat1, Kat14, Esco2, Mcm3ap) (Sheikh & Akhtar, 2018). Furthermore, as in mammals, different enzymes (Bloc1s1, Kat9, Kat12, Gtf3c1, Gtf3c2, Kat4, Nat10) described as non-well established KATs (Sheikh & Akhtar, 2018) are also identified. However, as thirty-seven KATs have been characterized in Humans (Sheikh & Akhtar, 2018), further improvement of new genome assembly might reveal missing members or confirm gene loss specific lineage. Presence of different acetyltransferase catalytic domains (Karmodiya et al., 2014; Roth et al., 2001; Sheikh & Akhtar, 2018), together with the phylogenetic conservation of the different KAT families highly suggest they are active proteins. Furthermore, as in other characterized species (Sheikh & Akhtar, 2018), additional conserved domains go in the sense that rivulus KATs might target specific substrates and may reflect distinct functions from just histone acetylation (Bedford et al., 2010). Finally, the KAT phylogenetic analysis reveals that teleost gene evolution is diversified and complex. Thus, while Kat5 is duplicated in Danio rerio (TsS3R), and undergoes a second round of CVT 10216 (Ss4R) in Salmoniform (Best et al., 2018), rivulus Kat5 seems to be not duplicated. In consequence, a complete molecular characterization of all rivulus Kat members is mandatory to achieve their evolutionary history. Overall, mRNA expression profiles of rivulus KAT showed specific patterns of expression through the embryonic development, and have tissue and sex specific levels in adult. However, as in zebrafish (Xu et al., 2016), based on the literature (Puthumana et al., 2017) and previous experiments (Fellous et al., 2018), we showed that Beta-Actin was the most stable during the embryonnic development, and that 18S-RNA was the most stable in adult, particularly between male and hermaphrodite individuals among the several tested reference gene candidates (RPL8, RP3, Beta-Actin, 18S-RNA). Based on this result, we demonstrated that rivulus KAT members are differentially expressed during the embryonnic development. Some of them (P300, Kat2a and Kat6a) that display very low mRNA levels in the early stages might be accumulated during the gametogenesis, while the others might be transcript during the zygotic activation. The peak of mRNA expression in gastrula stage for most of the rivulus KAT members is consistent with observations in mice, for which Kat8 is essential to development past the blastocyst stage (Thomas et al., 2007). Later in rivulus development, genes encoding KAT proteins were very highly expressed in the heart beat stage, the liver formation stage and the jaw formation stage, which are characterized by brain, lens and heart formations, liver formation and a developing jaw, respectively (Mourabit et al., 2011). We thus hypothesize that acetyltransferase enzymes might be crucial for rivulus organogenesis and embryos maturation. Indeed, they have been linked to development and skeletal regeneration in zebrafish (Banerji et al., 2016; Best et al., 2018; Karmodiya et al., 2014; Ree et al., 2015), while they are crucial to mice development (Vanyai et al., 2015; Yang, 2015), and are implicated in a range of developmental disorders in human (Sheikh & Akhtar, 2018). In adult rivulus, we demonstrated important differences in expression between males and hermaphrodites. However, cautions should be taken regarding the differences between tissues as 18S-RNA is not completely stable. For instance, our observations argue that KAT proteins may have important functions during rivulus gametogenesis. CBP/P300 and a particular histone H3 acetylation pattern are indeed necessary for spermatogenesis (Boussouar et al., 2014; Dai et al., 2015; Thomas et al., 2007) whereas Kat8 deficiency in oocyte leads to infertility (Yin et al., 2017) in mice. In fish, their roles in gametogenesis remain poorly described even if histones undergo acetylation during spermatogenesis in trout (Best et al., 2018) and zebrafish (Wu et al., 2011). Together with the mRNA levels in later embryonic stages, the rivulus KAT expression differences between males and hermaphrodites in brain underlie a putative role in neurogenesis. MYST have been indeed associated to neurons production in mice (Merson et al., 2006), while a P300 mutation is linked to the Rubistein-Taybi Syndrome (RSTS) characterized by intellectual disability in human (Bedford et al., 2010). Interestingly, knockdown of P300 in zebrafish leads to developmental defects similar to the RSTS that can be rescued (Babu et al., 2018) and remind the importance of epigenetic studies in fish.