THE TOMAJ MUTANT ALLELES OF ALPHA-TUBULIN67C REVEAL A REQUIREMENT FORTHE ENCODED MATERNAL SPECIFIC TUBULIN ISOFORM IN THE SPERM ASTER, THECLEAVAGE SPINDLE APPARATUS AND NEUROGENESIS DURING EMBRYONIC-DEVELOPMENT IN DROSOPHILA

The three dominant Tomaj(D) and their eleven revertant (Tomaj(R)) alle les have been localized to the alpha Tubulin67C gene of Drosophila mel anogaster., Although the meiotic divisions are normally completed in e ggs laid by Tortlaj(D)/+, Tomaj(D)/-, Tamaj(R)/-females, embryogenesis arrests prior to the gonomeric division. The arrest is caused by: (1) the failure of prominent sperm aster formation; and (2) a consequent lack of female pronuclear migration towards the male pronucleus. Conco mitant with the sperm aster defect, the four female meiotic products f use (tetra-fusion), similar to what is seen in eggs of wild-type virgi n females. Zn eggs of females heterozygous for weaker Tomaj(R) alleles , embryogenesis comes to a cessation before or shortly after cortical migration of cleavage nuclei. The apparent source of embryonic defect is the cleavage spindle apparatus. One of the three Tomaj(D) alleles i s cold-sensitive and its cold-sensitive period coincides with the comp letion of female meiosis and pronuclear migration. Disorganized centra l and peripheral nervous systems are also characteristic of embryos de rived from the temperature-sensitive Tomaj(D)/+ females. The Tomnj mut ant phenotypes indicate an involvement of the normal alpha Tubulin67C gene product in: (1) the formation of the sperm aster; (2) cleavage sp indle apparatus formation/function; and (3) the differentiation of the embryonic nervous system. The Tomaj(D) alleles encode a normal-sized alpha Tubulin67C isotype. Sequence analyses of the Tomaj(D) alleles re vealed the replacement in different positions of a single negatively c harged or neutral amino acid with a positively charged one. These resi dues presumably identify important functional sites.