Chen X, Reynolds E R, Ranganayakulu G, O'Donnell J M
Department of Biological Sciences, University of Alabama, Tuscaloosa 35487.
J Cell Sci. 1994 Dec;107 ( Pt 12):3501-13. doi: 10.1242/jcs.107.12.3501.
The Punch locus of Drosophila melanogaster encodes the pteridine biosynthesis enzyme guanosine triphosphate cyclohydrolase. One class of Punch mutants is defective for a maternal function that results in embryonic death. We demonstrate here that the embryos exhibit nuclear division defects during the precellular blastoderm stage of development. These defects include abnormal nuclear distribution, mitotic asynchrony, and persisting chromatin bridges. Daughter nuclei that do not complete chromosome separation nevertheless initiate new interphase and mitotic cycles. As a result, interconnected mitotic figures are observed. Mitotic spindles and nuclear envelopes appear essentially normal. A mutant phenocopy was induced in wild-type embryos by treatment with the guanosine triphosphate cyclohydrolase inhibitor, 2,4-diamino-6-hydroxypyrimidine, at a very early cleavage stage. Furthermore, an inhibitor of a terminal step in pteridine biosynthesis produced an identical phenotype. Immunolocalization experiments define expression of Punch protein in nurse cells during oogenesis. The protein is packaged into granules as it is transported into the oocyte cytoplasm. As syncytial blastoderm nuclear divisions proceed, Punch protein levels decrease and disappear by cellularization. Defects in the expression of the protein in Punch maternal effect mutants correlate well with the early phenotypes. These results show that a Punch product is directly involved in early nuclear divisions and suggest a possible role in chromosome separation.
黑腹果蝇的Punch基因座编码蝶啶生物合成酶鸟苷三磷酸环化水解酶。一类Punch突变体存在母源功能缺陷，导致胚胎死亡。我们在此证明，胚胎在发育的细胞前期胚盘阶段表现出核分裂缺陷。这些缺陷包括核分布异常、有丝分裂不同步以及持续存在的染色质桥。未完成染色体分离的子核仍会启动新的间期和有丝分裂周期。结果，观察到相互连接的有丝分裂图像。有丝分裂纺锤体和核膜基本正常。在非常早期的卵裂阶段，用鸟苷三磷酸环化水解酶抑制剂2,4-二氨基-6-羟基嘧啶处理野生型胚胎，可诱导出突变体表型。此外，蝶啶生物合成终末步骤的抑制剂产生了相同的表型。免疫定位实验确定了Punch蛋白在卵子发生过程中在滋养细胞中的表达。该蛋白在被转运到卵母细胞细胞质时被包装成颗粒。随着合胞体胚盘核分裂的进行，Punch蛋白水平下降，并在细胞化时消失。Punch母源效应突变体中该蛋白表达的缺陷与早期表型密切相关。这些结果表明，Punch产物直接参与早期核分裂，并提示其在染色体分离中可能发挥作用。
