, ▁several ▁model ▁organ isms ▁are ▁used ▁to ▁determine ▁what ▁mole cules ▁are ▁important ▁in ▁initi ating , ▁maintain ing ▁and ▁gu iding ▁moving ▁cells . ▁D ros oph ila ▁mel an og aster ▁is ▁one ▁of ▁the ▁favorite ▁organ isms ▁for ▁studying ▁bi ological ▁phen omena . ▁The ▁border ▁cells ▁of ▁the ▁D ros oph ila ▁ov ary ▁are ▁a ▁gen et ically ▁tract able ▁system ▁for ▁studying ▁diverse ▁aspects ▁of ▁moving ▁phen ot ype . ▁After ▁ident ifying ▁the ▁gen es ▁that ▁are ▁important ▁for ▁this ▁phen ot ype , ▁their ▁hom olog s ▁can ▁be ▁investig ated ▁for ▁put ative ▁roles ▁in ▁turning ▁non - in vas ive ▁cancer ous ▁tum ors ▁into ▁met ast atic ▁ones . ▁ ▁The ▁egg ▁chamber ▁of ▁the ▁D ros oph ila ▁ov ary ▁contains ▁ 1 6 ▁central ▁ger ml ine ▁cells ▁surrounded ▁by ▁a ▁mon ol ayer ▁ep ith el ium ▁of ▁about ▁ 1 0 0 0 ▁fol lic le ▁cells . ▁At ▁stage ▁ 9 ▁of ▁D ros oph ila ▁o ogen esis , ▁these ▁cells ▁perform ▁a ▁s tere ot yp ical ▁invas ive ▁migration ▁on ▁the ▁interven ing ▁nur se ▁cells , ▁and ▁reach ▁the ▁o ocy te . ▁The ▁migration ▁consists ▁of ▁an ▁initial ▁posterior ▁migration , ▁followed ▁by ▁another ▁in ▁the ▁d ors al ▁direction . ▁It ▁is ▁now ▁known ▁that ▁the ▁trans cription ▁factor ▁Sl bo ▁( slow ▁border ▁cells ) ▁is ▁a ▁master ▁reg ulator ▁of ▁the ▁mig rat ory ▁phen ot ype .