The objec­tive assigned to the ROBUST Project is to study the sta­bil­i­ty of cell cycles in Drosophi­la (or aka fruit flies) and there­by update the gene net­works involved in the process. This is the first col­lab­o­ra­tion between the UTC Applied Maths Lab­o­ra­to­ry (LMAC) and the Devel­op­ment Biol­o­gy Lab­o­ra­to­ry (LBD) at UPMC (Uni­ver­si­ty of Paris 6 – Pierre & Marie Curie); each team had to adapt to the work meth­ods and pro­to­cols of the oth­er team… 

Inves­ti­ga­tions on cell cycles are legion, notably because they relate to can­cer research pro­grammes. This is indeed the frame­work for the ROBUST project, finan­cial­ly sup­port­ed after a call for projects launched by the Sor­bonne Uni­ver­si­ties Clus­ter (SU) in 2014. 

“In fact, it was the UPMC-LBD Lab who con­tact­ed us, with the propo­si­tion that we mod­el part of their research work”, recalls Ghis­laine Gayraud, a research sci­en­tist at UTC-LMAC, The project — joint­ly ini­ti­at­ed by Ghis­laine Gayraud, Pas­cal Moy­al (who is also a research sci­en­tist at LMAC), Frédérique Per­on­net and Michel Gho (senior research sci­en­tists at the LBD) — start­ed in Octo­ber 2014 and was planned for one year. 

This study of cell cycle sta­bil­i­ty calls for a mod­el, devel­oped by Michel Gho’s team, of the mechano-sen­so­r­i­al bris­tles on the drosophi­la’s tho­rax. “The cells that com­pose the bris­tles on the fly­’s tho­rax under­go a spe­cial cell cycle known as an “endo­cy­cle””, explains Frédérique Per­on­net. “These cells cor­rect­ly repli­cate their genet­ic mate­r­i­al, but do not sub­di­vide, becom­ing ‘poly­ploid’. Poly­ploidy is asso­ci­at­ed with a high­er cell growth rate; hence, we can deduce that the length of the bris­tle is pro­por­tion­ate to the num­ber of endo­cy­cles is has under­gone by its cells and the vari­a­tion in bris­tle size also sig­nals vari­a­tions in the num­ber of endo­cy­cles involved”. 

The ROBUST Project mod­els the dis­tri­b­u­tion of bris­tles on the fly­’s body, inte­grat­ing bris­tle devel­op­ment through time. The result­ing growth pat­tern is filmed in Michel Gho’s lab and the bris­tles are visu­al­ized using var­i­ous flu­o­res­cent mark­ers. “Thanks to this exper­i­men­tal set-up, we are able to fol­low the num­ber of endo­cy­cles and hence the pro­gres­sion of bris­tle for­ma­tion”, details Michel Gho. Mod­el­ling the gen­e­sis of bris­tles allows us to bet­ter under­stand the devel­op­ment of these sen­so­ry organs.The obser­va­tions are then car­ried out under ref­er­ence con­di­tions those cor­re­spond­ing to “nor­mal” flies and again under con­di­tions where pro­tein cyclin G has an induced dereg­u­la­tion, dis­turb­ing the nor­mal func­tion. “Cyclin G has been a well-pre­served pro­tein dur­ing evo­lu­tion, notably in ver­te­brate ani­mals, with its two forms (G1 and G2)”, explains Frédérique Peronnet. 

“It now has been shown that they can be dereg­u­lat­ed in numer­ous car­cino­genic process­es, with­out our under­stand­ing what is the cause of the dis­tur­bance or the con­se­quence, i.e., the devel­op­ment of a can­cer. Our study aims at char­ac­ter­iz­ing the role of this pro­tein in the sta­bil­i­ty of the cell cycles? We use drosophi­la because we know it only hosts one cyclin G and that great­ly sim­pli­fies out inves­ti­ga­tions. The films we make will show the dynam­ics of the endo­cy­cles for each cell, depend­ing on whether it con­tains a dereg­u­lat­ed or non-dereg­u­lat­ed cyclin G, and in this way we hope to iden­ti­fy the final effect on bris­tle growth and what genes pre­cise­ly are involved in the growth pat­terns observed, ” adds Ghis­laine Gayraud. “If the num­ber of endo­cy­cles decreas­es, there will be less large cells and the bris­tles will be either trun­cat­ed short or sim­ply absent”. 

Last­ly, the gene net­works nec­es­sary for bris­tle devel­op­ment will be iden­ti­fied, by study­ing the dif­fer­ences in gene expres­sion in the cells that pre­cede growth of the bris­tles, under nor­mal con­di­tions and when the Cyclin G is dis­turbed. “Gene graph stud­ies are devel­op­ing rapid­ly today”, asserts Ghis­laine Gayraud. “In our par­tic­u­lar study, prob­a­bly only sev­er­al hun­dred genes were involved. That already is quite a large amount for a graph study, espe­cial­ly when there are lots of nodes, viz., the genes, but not that many sig­nif­i­cant links among them”. 

Once the gene char­ac­ter­is­tics have been iden­ti­fied, new exper­i­ments could be con­duct­ed for the pur­pose of iden­ti­fy­ing more pre­cise­ly their func­tion in bris­tle growth, as well as teach­ing us more about the role of the cyclin G.