Axon routing across the midline controlled by the Drosophila Derailed receptor.

In nervous systems with symmetry about the midline, many neurons project axons from one side to the other. Although several of the components controlling midline crossing have been identified, little is known about how axons choose the appropriate pathway when crossing. For example, in the Drosophila embryo axons cross the midline in one of two distinct tracts, the anterior or posterior commissure (AC or PC, respec tively). Here we show that the Derailed (Drl) receptor tyrosine kinase is expressed by neurons that project in the AC, and that in the absence of Drl such neurons often project abnormally into the PC. Conversely, misexpression of Drl in PC neurons forces them to cross in the AC. The behaviour of Drl-misexpressing neurons and the in vivo binding pattern of a soluble Drl receptor probe indicate that Drl acts as a guidance receptor for a repellent ligand present in the PC. Our results show that Drl is a novel component in the control of midline crossing.

Isolation and characterization of Dek, a Drosophila eph receptor protein tyrosine kinase.

We have isolated a Drosophila receptor protein tyrosine kinase (RTK) of the Eph subfamily. Dek, for Drosophila Eph kinase, possesses all the domains characteristic of the Eph subfamily of RTKs and is equally similar in sequence to both the EphA and the EphB subclasses. Antibody staining and promoter fusions to axon-targeted reporters reveal that Dek is expressed by a large subset of developing embryonic interneurons and is targeted to their axons and growth cones at the time of axon pathfinding. Dek is also expressed by photoreceptor cells of third-instar larvae as they project axons into the optic brain lobe. Misexpression and overexpression of full-length Dek or kinase-inactive Dek do not grossly affect axon pathfinding.

derailed is required for muscle attachment site selection in Drosophila.

During development, muscles must form and attach at highly stereotyped positions to allow for coordinated movements. In Drosophila, muscles grow towards and attach to specifically positioned cells within the epidermis. At the molecular level, very little is known about how muscles recognize these attachment sites. The derailed gene encodes a receptor tyrosine kinase family member that is essential for the pathfinding ability of expressing neurons. Here we show that the Drl RTK is also expressed by a small subset of developing embryonic muscles and neighboring epidermal cells during muscle attachment site selection. In drl mutants, these muscles often fail to attach at appropriate locations although their epidermal attachment cells appear unaffected. These results show that, similar to its role in neuronal pathway recognition, the Drl RTK participates in a mechanism required for muscle attachment site selection. The data suggest that both neurons and muscles use common mechanisms to recognize their paths or targets, and that Drl plays an analogous role in both developing systems.

The human cytomegalovirus IE2 86-kilodalton protein interacts with an early gene promoter via site-specific DNA binding and protein-protein associations.

The 86-kDa immediate-early 2 protein (IE2 86) of human cytomegalovirus is a powerful transactivator of homologous and heterologous promoters, including the human cytomegalovirus 1.2-kb RNA early promoter. Two potential mechanisms for gene activation by IE2 86 include interaction with cellular proteins and direct DNA binding. In this report, we show that the 1.2-kb RNA promoter contains a cis-acting AP-1 site, critical for its activation by IE2 86 in vivo, and that IE2 86, purified as a glutathione S-transferase-IE86 fusion protein, can interact with c-Jun and JunB. Additionally, by coimmunoprecipitation, we document that JunB and IE2 86 do associate in vivo. Further in vitro analysis reveals that Fos proteins are able to associate with glutathione S-transferase-IE86 only when present as a Jun-Fos heterodimer. With a set of IE2 86 mutants, we demonstrate that three independent regions of the IE2 86 interact in vitro with c-Jun, two of which are essential for activation of the 1.2-kb RNA promoter in vivo. We also show that IE2 86 can bind directly to this promoter through a sequence located just upstream of the AP-1 site between nucleotides -125 and -97. This discrete domain shares sequence homology with the cis-repression signal on the IE gene.

Control of neuronal pathway selection by a Drosophila receptor protein-tyrosine kinase family member.

During development, neurons are capable of selecting specific pathways that lead them to their appropriate target areas. A variety of molecular mechanisms are thought to be involved in pathway recognition, including cell adhesion, repulsion and chemotropism. However, apart from a few genes whose involvement has been shown genetically, the mechanisms underlying neuronal pathway selection are largely unknown. Here we report the isolation of the Drosophila derailed (drl) gene, which encodes a novel member of the receptor protein-tyrosine kinase family. Using a newly developed axon-targeted reporter gene we find that drl is expressed by a small subset of embryonic interneurons whose growth cones choose common pathways during development. In drl mutant embryos these neurons fail to make the correct pathway choices. Our results provide evidence for receptor protein-tyrosine kinase involvement in key aspects of neuronal pathway recognition.

Transactivation by the human cytomegalovirus IE2 86-kilodalton protein requires a domain that binds to both the TATA box-binding protein and the retinoblastoma protein.

The human cytomegalovirus major immediate-early (IE) proteins play an indispensable role in regulating viral gene expression. One of these gene products, the IE2 86-kDa protein (IE2 86), is a potent activator of both homologous and heterologous promoters and can form a complex with a component of the basal transcription apparatus, the TATA box-binding protein (TBP). In this report, we show that when IE2 86 is expressed as a glutathione S-transferase (GST)-IE2 86 fusion protein, there are three independent regions that can interact with TBP and with another important cellular regulatory protein, the retinoblastoma gene product (RB). One of these three regions, as well as a domain at the carboxy terminus, contain consensus sites for casein kinase phosphorylation and negatively regulate binding of in vitro-translated IE2 86 to GST-TBP or GST-RB. The dimerization domain of IE2 86 must be present for the interaction of the in vitro-translated protein with GST-TBP and GST-RB. Analysis of IE2 86 mutants in vivo demonstrates that one of the strong binding regions is required for the protein to function as a transactivator. Our results also indicate that domains other than those that interact with TBP and RB are required for the activation function of this protein.

Medical women of the West.

The presence in the West of women physicians with degrees from regular medical schools spans a period of approximately 130 years. Women's Medical College of Pennsylvania graduated many of these early women physicians. The first woman medical graduate of a western school was Lucy M. Field Wanzer, who finished in 1876 at the Department of Medicine, University of California in San Francisco. Soon thereafter, schools that would become Stanford University and the Oregon Health Sciences University schools of medicine, as well as the newly founded University of Southern California, were contributing to the pool of women physicians. The University of Michigan Medical School, the first coeducational state medical school, also educated some of the western women physicians, who by 1910 numbered about 155. This regional account of the progress of women physicians as they strove to become an integral part of the profession emphasizes the familiar themes of altruism, ingenuity, and perseverance that characterized their efforts.