The gnu mutation of Drosophila causes inappropriate DNA synthesis in unfertilized and fertilized eggs

Abstract

7he 9nu mutat10n 0f Dr050ph11a cau5e5 1nappr0pr1ate DNA 5ynthe515 1n unfert1112ed and fert1112ed e995Matthew Freeman 1 and Dav1d M. 610verCancer Re5earch Campa19n, Eukary0t1c M01ecu1ar 6enet1c5 Re5earch 6r0up, Department 0f 810chem15try, 1mper1a1 C011e9e 0f 5c1ence and 7echn0109Y, L0nd0n 5W7 2A2, UK Dr050ph11a me1an09a5ter em6ry05 wh05e m0ther5 are h0m02Y90u5 f0r the materna1 effect 1etha1 mutat10n 9nu (6NU em6ry05) under90 DNA 5ynthe515 6ut n0 nuc1ear d1v1510n; th15 1ead5 t0 the f0rmat10n 0f a 5ma11 num6er 0f 91ant nuc1e1 1n the 5yncyt1a1 61a5t0derm. We have 5h0wn prev10u51y that many c0mp0nent5 0f the m1t0t1c apparatu5 are pre5ent and funct10na1 1n 6NU em6ry05, and the pr1mary 1e510n 0f the 9nu mutat10n ha5 theref0re rema1ned 065cure. Here, we rep0rt that fert1112at10n 15 n0t nece55ary f0r 6NU e995 t0 deve10p. 61ant nuc1e1 0r191nate fr0m the pr0duct5 0f fema1e me10515, and we 5ee aut0n0m0u51y rep11cat1n9 centr050me5 that mu5t 6e materna11y der1ved. 1f 6NU e995 are 1n5em1nated, h0wever, the ma1e pr0nuc1eu5 a150 under90e5 DNA rep11cat10n. 0ur 065ervat10n5 5u99e5t that the 6NU cyt0p1a5m perm1t5 DNA 5ynthe515 1n a re1at1ve1y unre9u1ated manner. 1n em6ry05 fr0m fema1e5 h0m02Y90u5 f0r 9nu and the fema1e 5ter11e hap101d mutat10n mh, we f1nd rep11cat10n 0f DNA der1ved fr0m the ma1e pr0nuc1eu5. 7h15 c0ntra5t5 w1th em6ry05 fr0m m0ther5 h0m02y90u5 f0r mh a10ne, 1n wh1ch th15 d0e5 n0t 0ccur. We pr0p05e that the 9nu 9ene pr0duct part1c1pate5 1n the repre5510n 0f DNA 5ynthe515 f0und 1n unfert1112ed e995.[Key W0rd5: Dr050ph11a; DNA rep11cat10n; e99 act1vat10n] L1tt1e 15 kn0wn a60ut the pr0ce55e5 that re9u1ate the act1vat10n 0f DNA 5ynthe515 and the 5u65e4uent 0n5et 0f the m1t0t1c cyc1e 1n fert1112ed e995. A1th0u9h exten51ve 610chem1ca1 5tudy, ma1n1y 0f amph161an e995, ha5 dem0n5trated the 1nv01vement 0f 5evera1 fact0r5, 5uch a5 maturat10n-pr0m0t1n9 fact0r (MPF) (Wu anad 6erhart 1980; M1ake-Lye et a1. 1983), the m01ecu1ar 6a515 f0r th15 u614u1t0u5 deve10pmenta1 5w1tch 15 5t111 unc1ear. 7he ear11e5t 5ta9e5 0f em6ry09ene515 are ea511y 065erved 1n Dr050ph11a e995, and, c0up1ed w1th the 50ph15t1cated 9e-net1c and m01ecu1ar techn14ue5 ava11a61e, th15 make5 Dr050ph11a an attract1ve 0r9an15m w1th wh1ch t0 5tudy the5e event5. 1n th15 rep0rt we dem0n5trate that 9nu 9ene pr0duct 0f Dr050ph11a 15 1nv01ved 1n the repre5510n 0f DNA rep11cat10n that 0ccur5 1n unfert1112ed e995.9nu 15 a matema1 effect 1etha1 mutat10n 0f Dr050ph11a me1an09a5ter, wh1ch map5 0n the th1rd chr0m050me at 42.5 map un1t5. 1t ha5 the 5tr1k1n9 phen0type that em6ry05 wh05e m0ther5 are h0m02y90u5 f0r the mutat10n (6NU em6ry05) under90 DNA 5ynthe515 6ut n0 nuc1ear d1v1510n. 7h15 1ead5 t0 the f0rmat10n 0f a 5yncyt1a1 61a5-t0derm that c0nta1n5 a 5maU num6er 0f 91ant nuc1e1 1n-5tead 0f the n0rma1 rap1d1y d1v1d1n9 d1p101d nuc1e1 5een 1n w11d-type em6ry05; 6NU em6ry05 never ce11u1ar12e (Freeman et a1. 1986). 7h15 phen0type 1ed u5 t0 6e11eve that the pr0duct 0f the 9nu 9ene part1c1pate5 1n the m1-1Pre5ent addre55: Department 0f 810chem15try, Un1ver51ty 0f Ca11f0rn1a, 8erke1e...

Regulation of Cyclin A protein in meiosis and early embryogenesis

“…Renewed translation of Cyclin B after the completion of meiosis is dependent on the PNG kinase complex, which acts by both poly(A) dependent and independent mechanisms (4). In the absence of PNG function meiosis is completed, but the meiotic products persist in an interphase state, undergoing DNA replication but not mitosis to produce giant, polyploid nuclei (11,12).…”

Drosophila PLUTONIUM protein is a specialized cell cycle regulator required at the onset of embryogenesis.

“…Mothers mutant for three of five png alleles produce embryos like those from plu or gnu mutant mothers ( Figure 2F). However, mothers mutant for the This phenotype is identical to that of plu and gnu mutants (Freeman et al, 1986;Freeman and Glover, 1987;Shamanski and Orr-Weaver, 1991). other two alleles lay fertilized eggs in which S-phase is transiently linked to mitosis to produce up to 16 nuclei ( Figure 2D). In these embryos, the polar bodies begin to overreplicate while the zygotic nuclei still appear to be undergoing normal S-M cycles.…”

“…Females homozygous for these mutations produce unfertilized eggs which inappropriately replicate the four meiotic products. Fertilized embryos from gnu mutant mothers appear to be identical to those from plu mutants in that DNA replication occurs but there is no nuclear division (Freeman et al, 1986;Freeman and Glover, 1987;Shamanski and Orr-Weaver, 1991). In contrast, the phenotype of fertilized png embryos reveals that there are two classes of png mutant alleles.…”

“…Other mutants examined were gnu, cortQW55, grauQE7 , and dhd'8 (Freeman et al, 1986;Freeman and Glover, 1987;Salz et al, 1994;Page and Orr-Weaver, 1996). The deficiency Df(1)A94 deletes png and was used as a control in some experiments.…”

“…The maternal-effect genes plutonium (plu),1 pan gu (png), and giant nuclei (gnu) act to control S-phase in the unfertilized egg and during the early divisions (Freeman et al, 1986;Freeman and Glover, 1987;Shamanski and Orr-Weaver, 1991). Mothers mutant for any one of these genes produce unfertilized eggs that properly complete meiosis; however, DNA replication inappropriately occurs in all four meiotic products in these mutant eggs, leading to giant polyploid nuclei.…”