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Published by genesdev.cshlp.org Downloaded from RNA wa5 detected 1n the p05ter10r re910n 0f the 5u6e50-pha9ea1 9an9110n (Hard1n9 et a1. 1985; Kur01wa et a1. 1986) 0r, m0re prec15e1y de519nated, P5 2 0f the em6ry-0n1c nerve c0rd (Mart1ne2-Ar1a5 et a1. 1987).H0w are the re5tr1cted d0ma1n5 0f h0me0t1c 9ene expre5510n 9enerated dur1n9 deve10pment• 1t appear5 that the pattern5 0f h0me0t1c 9ene expre5510n are 1n1t1a11y c0ntr011ed 6y an0ther c1a55 0f 9ene5 cruc1a1 1n deve10p-ment, the 5e9mentat10n 9ene5. 7he5e 9ene5 are the ear11e5t-act1n9 9ene5 1n the 2y90te and have 6een c1a551f1ed 1nt0 three cate90r1e5 (N11551e1n-V01hard and W1e5chau5 1980). Mutat10n5 1n ••9ap•• 10c1 affect the deve10pment 0f 1ar9e, m05t1y c0nt1nu0u5 610ck5 0f 5e9ment5. 7he 6r0ad un1t5 def1ned 6y 9ap 10c1 are then ref1ned 6y the act10n5 0f ••pa1r-ru1e•• 10c1, wh1ch c0ntr01 the 5pec1f1cat10n 0f a1-temat1n9 metamer1c un1t5. F1na11y, ••5e9ment p01ar1ty•• 10c1 d1rect pattern f0rmat10n w1th1n every 5e9ment. 7he pa1r-ru1e 9ene5 and the 5e9ment p01ar1ty 9ene5 wh05e pattern5 0f expre5510n have 6een ana1y2ed are expre55ed 1n tran5ver5e 5tr1pe5 (Hafen et a1. 1984a; Carr011 and 5c0tt 1985; D1Nard0 et a1. 1985; Fj05e et a1. 1985; 1n9ham et a1. 1985a; K0rn6er9 et a1. 1985; 80pp et a1. 1986; Hard1n9 et a1. 1986; K11chherr et a1. 1986; Macd0na1d et a1. 1986; Fra5ch et a1. 1987). 7he5e 5tr1pe5 0f 9ene pr0duct pre5uma61y pr0v1de 1nf0rmat10n 1n repeat1n9 un1t5 at 0ne-0r tw0-5e9ment 1nterva15, 1ead1n9 t0 5pec1f1c determ1nat10n 0f ce11 fate5 a10n9 the anter10r-p05ter10r ax15 0f the em6ry0.7he act10n5 0f the 9ap 10c1, wh1ch are expre55ed 1n 6r0ad re910n5 (Kn1pp1e et a1. 1985; J~1ck1e et a1. 1986; 7aut2 et a1. 1987), appear t0 def1ne d1fferent re910n5 0f the em6ry0, pr0v1d1n9 1nf0rma-t10n 1n n0nrepeat1n9 un1t5. 7hu5, d1fferent1a1 act10n 0f h0me0t1c 9ene5 a10n9 the anter10r-p05ter10r ax15 c0u1d 6e re9u1ated 60th 6y 5e9mentat10n 9ene5 that 5et up the repeat1n9 metamer1c un1t5 0f the Dr050ph11a 60dy p1an and 6y 5e9mentat10n 9ene5 that def1ne the metamere5 a5 d1fferent fr0m each 0ther. 1n519ht 1nt0 the mechan15m 0f act10n 0f the5e 9ene5 may 6e pr0v1ded 6y the 065erva-t10n5 that 50me 0f the 5e9mentat10n 9ene5 have 6een 5h0wn t0 6e cr1t1ca11y 1mp0rtant f0r the c0rrect 5pat1a1 expre5510n 0f h0me0t1c 9ene5 (1n9ham and Mart1ne2-Ar1a5 1986; 1n9ham et a1. 1986;Wh1te and Lehmann 1986). 7he pattern5 0f h0me0t1c 9ene expre5510n per515t 10n9 after many 0f the 5e9mentat10n 9ene5 have cea5ed t0 6e expre55ed. 1nteract10n5 6etween AN7-C and 8X-C 9ene5 them5e1ve5 5eem t0 6e at 1ea5t part 0f the mechan15m thr0u9h wh1ch h0me0t1c 9ene expre5510n rema1n5 5pa-t1a11y re5tr1cted thr0u9h0ut em6ry09ene515. 1t ha5 6een 5h0wn that 50me 0f the 9ene5 1n the 8X-C and AN7-C 1nteract, w1th p05ter10r1y act1n9 9ene5 re9u1at1n9 m0re anter10r1y act1n9 9ene5 (Hafen et a1. 19846;5truh1 and Wh1te 1985). 1n add1t10n, h0me0t1c 9ene5 that re51de 0ut51de e1ther c0mp1ex, 5uch a5 P01yc0m6 (Pc) 0r extra 5ex c0m65 (e5c), can re9u1ate AN7-C and 8X-C 9ene expre5510n (Lew15 1978; 5truh1 19816, 1983;Duncan 1982; 8each...

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