Deletion analysis of the Drosophila Inscuteable protein reveals domains for cortical localization and asymmetric localization.
The Drosophila Inscuteable protein acts as a key regulator of asymmetric cell division during the development of the nervous system  . In neuroblasts, Inscuteable localizes into an apical cortical crescent during late interphase and most of mitosis. During mitosis, Inscuteable is required for the correct apical-basal orientation of the mitotic spindle and for the asymmetric segregation of the proteins Numb   , Prospero    and Miranda   into the basal daughter cell. When Inscuteable is ectopically expressed in epidermal cells, which normally orient their mitotic spindle parallel to the embryo surface, these cells reorient their mitotic spindle and divide perpendicularly to the surface . Like the Inscuteable protein, the inscuteable RNA is asymmetrically localized . We show here that inscuteable RNA localization is not required for Inscuteable protein localization. We found that a central 364 amino acid domain - the Inscuteable asymmetry domain - was necessary and sufficient for Inscuteable localization and function. Within this domain, a separate 100 amino acid region was required for asymmetric localization along the cortex, whereas a 158 amino acid region directed localization to the cell cortex. The same 158 amino acid fragment could localize asymmetrically when coexpressed with the full-length protein, however, and could bind to Inscuteable in vitro, suggesting that this domain may be involved in the self-association of Inscuteable in vivo. (+info)
Sibling cell fate in the Drosophila adult external sense organ lineage is specified by prospero function, which is regulated by Numb and Notch.
Specification of cell fate in the adult sensory organs is known to be dependent on intrinsic and extrinsic signals. We show that the homeodomain transcription factor Prospero (Pros) acts as an intrinsic signal for the specification of cell fates within the mechanosensory lineage. The sensory organ precursors divide to give rise to two secondary progenitors - PIIa and PIIb. Pros is expressed in PIIb, which gives rise to the neuron and thecogen cells. Loss of Pros function affects the identity of PIIb and neurons fail to differentiate. Pros misexpression is sufficient for the transformation of PIIa to PIIb fate. The expression of Pros in the normal PIIb cell appears to be regulated by Notch signaling. (+info)
A functional analysis of inscuteable and its roles during Drosophila asymmetric cell divisions.
Cellular diversity in the Drosophila central nervous system is generated through a series of asymmetric cell divisions in which one progenitor produces two daughter cells with distinct fates. Asymmetric basal cortical localisation and segregation of the determinant Prospero during neuroblast cell divisions play a crucial role in effecting distinct cell fates for the progeny sibling neuroblast and ganglion mother cell. Similarly asymmetric localisation and segregation of the determinant Numb during ganglion mother cell divisions ensure that the progeny sibling neurons attain distinct fates. The most upstream component identified so far which acts to organise both neuroblast and ganglion mother cell asymmetric divisions is encoded by inscuteable. The Inscuteable protein is itself asymmetrically localised to the apical cell cortex and is required both for the basal localisation of the cell fate determinants during mitosis and for the orientation of the mitotic spindle along the apical/basal axis. Here we define the functional domains of Inscuteable. We show that aa252-578 appear sufficient to effect all aspects of its function, however, the precise requirements for its various functions differ. The region, aa288-497, is necessary and sufficient for apical cortical localisation and for mitotic spindle (re)orientation along the apical/basal axis. A larger region aa288-540 is necessary and sufficient for asymmetric Numb localisation and segregation; however, correct localisation of Miranda and Prospero requires additional sequences from aa540-578. The requirement for the resolution of distinct sibling neuronal fates appears to coincide with the region necessary and sufficient for Numb localisation (aa288-540). Our data suggest that apical localisation of the Inscuteable protein is a necessary prerequisite for all other aspects of its function. Finally, we show that although inscuteable RNA is normally apically localised, RNA localisation is not required for protein localisation or any aspects of inscuteable function. (+info)
Effect of juvenile hormone on the central nervous processing of sex pheromone in an insect.
Behavioral sex pheromone responsiveness in the male moth Agrotis ipsilon was previously shown to be controlled by juvenile hormone (JH). However, this morphogenetic hormone did not change the sensitivity of antennae to sex pheromones. To analyze the possible involvement of JH in the central integration of the female-produced sex pheromone, we investigated the pheromone response of olfactory antennal lobe (AL) interneurons in male A. ipsilon as a function of age and JH status by using intracellular recordings. When the antennae were stimulated with the sex pheromone blend, the sensitivity of olfactory AL neurons increased with age, as does the JH-dependent behavioral and physiological development of A. ipsilon males. Furthermore, males surgically deprived of JH showed a significant decrease in the sensitivity of the AL neurons. JH injection in operated or in young males restored or induced, respectively, a high sensitivity of the AL neurons. JH seems likely to be involved in the plasticity of the adult insect brain by modulating the central nervous processing of olfactory information, thus allowing mate recognition and reproduction at the optimal time. (+info)
Cell division genes promote asymmetric interaction between Numb and Notch in the Drosophila CNS.
Cell intrinsic and cell extrinsic factors mediate asymmetric cell divisions during neurogenesis in the Drosophila embryo. In the NB4-2->GMC-1->RP2/sib lineage, one of the well-studied neuronal lineages in the ventral nerve cord, the Notch (N) signaling interacts with the asymmetrically localized Numb (Nb) to specify sibling neuronal fates to daughter cells of GMC-1. In this current study, we have investigated asymmetric cell fate specifications by N and Nb in the context of cell cycle. We have used loss-of-function mutations in N and nb, cell division mutants cyclinA (cycA), regulator of cyclin A1 (rca1) and string/cdc25 phosphatase (stg), and the microtubule destabilizing agent, nocodazole, to investigate this issue. We report that the loss of cycA, rca1 or stg leads to a block in the division of GMC-1, however, this GMC-1 exclusively adopts an RP2 identity. While the loss of N leads to the specification of RP2 fates to both progeny of GMC-1 and loss of nb results in the specification of sib fates to these daughter cells, the GMC-1 in the double mutant between nb and cycA assumes a sib fate. These epistasis results indicate that both N and nb function downstream of cell division genes and that progression through cell cycle is required for the asymmetric localization of Nb. In the absence of entry to metaphase, the Nb protein prevents the N signaling from specifying sib fate to the RP2/sib precursor. These results are also consistent with our finding that the sib cell is specified as RP2 in N; nb double mutants. Finally, our results show that nocodazole-arrested GMC-1 in wild-type embryos randomly assumes either an RP2 fate or a sib fate. This suggests that microtubules are involved in mediating the antagonistic interaction between Nb and N during RP2 and sib fate specification. (+info)
The Drosophila homeobox genes zfh-1 and even-skipped are required for cardiac-specific differentiation of a numb-dependent lineage decision.
A series of inductive signals are necessary to subdivide the mesoderm in order to allow the formation of the progenitor cells of the heart. Mesoderm-endogenous transcription factors, such as those encoded by twist and tinman, seem to cooperate with these signals to confer correct context and competence for a cardiac cell fate. Additional factors are likely to be required for the appropriate specification of individual cell types within the forming heart. Similar to tinman, the zinc finger- and homeobox-containing gene, zfh-1, is expressed in the early mesoderm and later in the forming heart, suggesting a possible role in heart development. Here, we show that zfh-1 is specifically required for formation of the even-skipped (eve)-expressing subset of pericardial cells (EPCs), without affecting the formation of their siblings, the founders of a dorsal body wall muscle (DA1). In addition to zfh-1, mesodermal eve itself appears to be needed for correct EPC differentiation, possibly as a direct target of zfh-1. Epistasis experiments show that zfh-1 specifies EPC development independently of numb, the lineage gene that controls DA1 founder versus EPC cell fate. We discuss the combinatorial control mechanisms that specify the EPC cell fate in a spatially precise pattern within the embryo. (+info)
NUMB localizes in the basal cortex of mitotic avian neuroepithelial cells and modulates neuronal differentiation by binding to NOTCH-1.
The importance of lateral inhibition mediated by NOTCH signaling is well demonstrated to control neurogenesis both in invertebrates and vertebrates. We have identified the chicken homolog of Drosophila numb, which suppresses NOTCH signaling. We show that chicken NUMB (c-NUMB) protein is localized to the basal cortex of mitotic neuroepithelial cells, suggesting that c-NUMB regulates neurogenesis by the modification of NOTCH signaling through asymmetrical cell division. Consistent with this suggestion, we show (1) that c-NUMB interferes with the nuclear translocation of activated c-NOTCH-1 through direct binding to the PEST sequence in the cytoplasmic domain of c-NOTCH-1 and (2) that c-NUMB interferes with c-NOTCH-1-mediated inhibition of neuronal differentiation. (+info)
Experience-expectant plasticity in the mushroom bodies of the honeybee.
Worker honeybees (Apis mellifera) were reared in social isolation in complete darkness to assess the effects of experience on growth of the neuropil of the mushroom bodies (MBs) during adult life. Comparison of the volume of the MBs of 1-day-old and 7-day-old bees showed that a significant increase in volume in the MB neuropil occurred during the first week of life in bees reared under these highly deprived conditions. All regions of the MB neuropil experienced a significant increase in volume with the exception of the basal ring. Measurement of titers of juvenile hormone JH) in a subset of bees indicated that, as in previous studies, these rearing conditions induced in some bees the endocrine state of high JH associated with foraging, but there was no correlation between JH titer and volume of MB neuropil. Treatment of another subset of dark-reared bees with the JH analog, methoprene, also had no effect of the growth of the MB neuropil. These results demonstrate that there is a phase of MB neuropil growth early in the adult life of bees that occurs independent of light or any form of social interaction. Together with previous findings showing that an increase in MB neuropil volume begins around the time that orientation flights occur and then continues throughout the phase of life devoted to foraging, these results suggest that growth of the MB neuropil in adult bees may have both experience-expectant and experience-dependent components. (+info)