Xy. Chen et al., A MATERNAL PRODUCT OF THE PUNCH LOCUS OF DROSOPHILA-MELANOGASTER IS REQUIRED FOR PRECELLULAR BLASTODERM NUCLEAR DIVISIONS, Journal of Cell Science, 107, 1994, pp. 3501-3513
The Punch locus of Drosophila melanogaster encodes the pteridine biosy
nthesis enzyme guanosine triphosphate cyclohydrolase. One class of Pun
ch mutants is defective for a maternal function that results in embryo
nic death. We demonstrate here that the embryos exhibit nuclear divisi
on defects during the precellular blastoderm stage of development. The
se defects include abnormal nuclear distribution, mitotic asynchrony,
and persisting chromatin bridges. Daughter nuclei that do not complete
chromosome separation nevertheless initiate new interphase and mitoti
c cycles. As a result, interconnected mitotic figures are observed. Mi
totic spindles and nuclear envelopes appear essentially normal. A muta
nt phenocopy was induced in wild-type embryos by treatment with the gu
anosine triphosphate cyclohydrolase inhibitor, 2,4-diamino-6-hydroxypy
rimidine, at a very early cleavage stage. Furthermore, an inhibitor of
a terminal step in pteridine biosynthesis produced an identical pheno
type. Immunolocalization experiments define expression of Punch protei
n in nurse cells during oogenesis, The protein is packaged into granul
es as it is transported into the oocyte cytoplasm. As syncytial blasto
derm nuclear divisions proceed, Punch protein levels decrease and disa
ppear 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 earl
y nuclear divisions and suggest a possible role in chromosome separati
on.