Expanding the view of Clock and cycle gene evolution in Diptera

Abstract

We expanded the view of Clock (Clk) and cycle (cyc) gene evolution in Diptera by studying the fruit fly Anastrepha fraterculus (Afra), a Brachycera. Despite the high conservation of clock genes amongst insect groups, striking structural and functional differences of some clocks have appeared throughout evolution. Clk and cyc nucleotide sequences and corresponding proteins were characterized, along with their mRNA expression data, to provide an evolutionary overview in the two major groups of Diptera: Lower Diptera and Higher Brachycera. We found that AfraCYC lacks the BMAL (Brain and muscle ARNT-like) C-terminus region (BCTR) domain and is constitutively expressed, suggesting that AfraCLK has the main transactivation function, which is corroborated by the presence of poly-Q repeats and an oscillatory pattern. Our analysis suggests that the loss of BCTR in CYC is not exclusive of drosophilids, as it also occurs in other Acalyptratae flies such as tephritids and drosophilids, however, but it is also present in some Calyptratae, such as Muscidae, Calliphoridae and Sarcophagidae. This indicates that BCTR is missing from CYC of all higher-level Brachycera and that it was lost during the evolution of Lower Brachycera. Thus, we can infer that CLK protein may play the main role in the CLK\CYC transcription complex in these flies, like in its Drosophila orthologues.

The characterization of the circadian clock in the olive fly Bactrocera oleae (Diptera: Tephritidae) reveals a Drosophila-like organization

“…This alternative form encodes a peptide that carries an extra domain at the C-terminus (BCTR, BMAL C-terminus region) working as transactivation domain required for binding and activating transcription of the per gene. Most probably because of this, cyc is rhythmically expressed in mosquitoes 35 , 36 , whereas in Drosophila and other higher Diptera (=Brachycera) it is constantly expressed 32 , 37 , 38 . Here we report that B. oleae cyc shares the same features as cyc in other Brachycera flies.…”

“…Most likely, the CYC and CLK found in lower Diptera are the ancestral forms that are conserved in most insects and mammals. During evolution, the higher Diptera (Brachycera) seem to have lost the BCTR activation domains at the C-terminus of CYC but gained the poly-Q repeats at the C-terminus of CLK (see 38 for discussion). Bactrocera oleae , belonging to the higher Diptera (Brachycera; family Tephritidae), fits perfectly into this picture.…”

Model and Non-model Insects in Chronobiology

“…Similarly conserved are the general mechanisms of molecular rhythm generation that involve several other clock genes and proteins that interact in transcriptional/translational feedback loops. Nevertheless, a few features are unique to D. melanogaster, or better to say to higher flies (Brachycera) (Sandrelli et al, 2008;Tomioka and Matsumoto, 2015;Chahad-Ehlers, 2017;Bertolini et al, 2018). For example, the second discovered fly clock gene, timeless1 (tim1 or dtim) has a unique function in the first transcriptional/translational feedback loop of higher flies, where its protein product TIM1 dimerizes with PER (the protein product of the period gene) and the dimer enters the nucleus (Sehgal et al, 1994;Myers et al, 1996;Saez and Young, 1996) (see Figure 1).…”

“…The basic negative feedback mechanism is very similar in all animals (although gene sets differ), but again there are unique features in higher flies. While CYC (also called BMAL1 in mammals) is the component that binds to the E-boxes and activates transcription of per and tim1/cry2 in the great majority of animals (including bees), CLK is the relevant transcriptional activator in higher flies (Bae et al, 1998;Chang et al, 2003;Rubin et al, 2006;Yuan et al, 2007;Sandrelli et al, 2008;Tomioka and Matsumoto, 2015;Chahad-Ehlers, 2017) (see Figure 1). Most interestingly, the transcription of the clock factor that possesses the transactivation domain is controlled in a rhythmic manner through a second feedback loop, while the one without transactivation domain is not rhythmically controlled.…”

Flies as models for circadian clock adaptation to environmental challenges

“…The Brachycera comprise about 120 families. Species of the following families have been investigated with respect to their rhythms: Tephritidae (An et al., ; An, Tebo, Song, Frommer, & Raphael, ; Bertolini et al., ; Chahad‐Ehlers et al., ; Fuchikawa et al., ; Matsumoto et al., ; Mazzotta et al., ; Miyatake et al., ), Phoridae (Bostock, Green, Kyriacou, & Vanin, ), Calliphoridae (Muguruma, Goto, Numata, & Shiga, ; Saunders, ; Smith, ; Shiga & Numata, ; Warman, Newcomb, Lewis, & Evans, ; Yasuyama, Hase, & Shiga, ), Sarcophagidae (Goto & Denlinger, ; Koštál, Závodská, & Denlinger, ; Yamamoto, Nishimura, & Shiga, ; Yamamoto, Shiga, & Goto, ), Muscidae (Codd et al., ; Bazalova & Dolezel, ; Pyza & Meinertzhagen, ; Pyza, Siuta, & Tanimura, ), and Drosophilidae (see below) (Figure a). Among these, the genetic and neuronal basis of the circadian clock was revealed for the house fly M. domestica (Codd et al., ), the blow fly Protophormia terraenovae (Muguruma et al., ) and recently also for the olive fly, Bactrocera oleae (Bertolini et al., ).…”