The mushroom body defect Gene Product Is an Essential Component of the Meiosis II Spindle Apparatus in Drosophila Oocytes

Abstract

In addition to their well-known effects on the development of the mushroom body, mud mutants are also female sterile. Here we show that, although the early steps of ovary development are grossly normal, a defect becomes apparent in meiosis II when the two component spindles fail to cohere and align properly. The products of meiosis are consequently mispositioned within the egg and, with or without fertilization, soon undergo asynchronous and spatially disorganized replication. In wild-type eggs, Mud is found associated with the central spindle pole body that lies between the two spindles of meiosis II. The mutant defect thus implies that Mud should be added to the short list of components that are required for the formation and/or stability of this structure. Mud protein is also normally found in association with other structures during egg development: at the spindle poles of meiosis I, at the spindle poles of early cleavage and syncytial embryos, in the rosettes formed from the unfertilized products of meiosis, with the fusomes and spectrosomes that anchor the spindles of dividing cystoblasts, and at the nuclear rim of the developing oocyte. In contrast to its important role at the central spindle pole body, in none of these cases is it clear that Mud plays an essential role. But the commonalities in its location suggest potential roles for the protein in development of other tissues.

Microtubule-driven nuclear rotations promote meiotic chromosome dynamics

“…We focused on Mud (Mushroom body defect), the Drosophila homologue of NuMA, for several reasons: vertebrate NuMA is known to interact directly with Dynein to assemble the mitotic spindle, and its Drosophila and C. elegans homologues interact with Dynein to position the spindle in neuroblasts and the one-cell stage embryo [52][53][54][55][56] ; mud null alleles are viable but females are sterile and males are fertile, indicating a specific requirement for mud in female germ cell development; Mud is an essential component of the meiosis II spindle in Drosophila oocyte 57 ; and Mud is expressed in the germarium and localizes to the nuclear envelope 57 (Figs 7a and 8f).…”

PIP5K-dependent production of PIP2 sustains microtubule organization to establish polarized transport in theDrosophilaoocyte

“…Pins requirement has not been reported in the oocyte. However, Mud is distributed around the nucleus (Yu et al, 2006), like the Dynein-Dynactin complex with which it has been reported to control spindle attachment in other systems (Gonczy, 2008). However, although the positioning of the nucleus is Dynein dependent (Januschke et al, 2002), it does not necessarily require Mud (Yu et al, 2006).…”

Mars, aDrosophilaprotein related to vertebrate HURP, is required for the attachment of centrosomes to the mitotic spindle during syncytial nuclear divisions

“…The Mushroom body defect (Mud) protein shows limited sequence similarity to NuMa and was shown to bind Pins, the fly homolog of the NuMa binding partner Lgn (Bowman et al, 2006;Izumi et al, 2006;Siller et al, 2006). Mud is required for correct spindle orientation in neuroblasts (Bowman et al, 2006;Izumi et al, 2006;Siller et al, 2006) and for meiosis II in female flies (Yu et al, 2006), but a function in spindle pole organization has not been demonstrated so far. The protein encoded by abnormal spindle (asp) localizes to microtubule minus ends at metaphase spindle poles and is required for focussing of spindle poles (Saunders et al, 1997; do Carmo Avides and Glover,…”