Characterization of the plant Notchless homolog, a WD repeat protein involved in seed development.

We have isolated a plant NOTCHLESS (NLE) homolog from the wild potato species Solanum chacoense Bitt., encoding a WD-repeat containing protein initially characterized as a negative regulator of the Notch receptor in animals. Although no Notch signaling pathway exists in plants, the NLE gene is conserved in animals, plants, and yeast. Overexpression of the plant ScNLE gene in Drosophila similarly affected bristle formation when compared to the overexpression of the endogenous Drosophila NLE gene, suggesting functional conservation. Expression analyses showed that the ScNLE gene was fertilization-induced and primarily expressed in ovules after fertilization, mainly in the integumentary tapetum (endothelium). Significant expression was also detected in the shoot apex. Promoter deletion analysis revealed that the ScNLE promoter had a complex modulatory architecture with both positive, negative, and tissue specific regulatory elements. Transgenic plants with reduced levels of ScNLE transcripts displayed pleitotropic phenotypes including a severe reduction in seed set, consistent with ScNLE gene expression pattern.

atonal is required for exoskeletal joint formation in the Drosophila auditory system.

Hearing relies on the delicate arrangement of mechanoreceptor neurones and an acoustomechanical interface. The concerted action of these neural and non-neural components is essential to audition, raising the question of whether they also develop in a concerted way. Drosophila hears with its antennae. A specialized antennal joint allows the distal part of the antenna to vibrate in response to sound and, thus, to serve as the sound receiver. This receiver's vibration is transduced by a chordotonal sense organ (CHO) that is closely associated with the joint. Here, we report that atonal (ato), the proneural gene for CHOs, is required for the formation of this antennal joint. Biophysical measurements in hemi- and homozygous ato(1) mutant flies show that, in addition to eliminating the auditory CHO, loss of ato function makes the antennal receiver insensitive to sound, impairing its auditory function. Anatomically, the cause for this mechanical effect resides in the deprivation of mobile exoskeletal joint structures. Hence, ato, the homologue of mouse Math1, is required for the formation of both the auditory CHO and joint, providing a genetic link between the very neural and exoskeletal components that together transform fly antennae into ears.

Localization of choline acetyltransferase-expressing neurons in Drosophila nervous system.

A variety of approaches have been developed to localize neurons and neural elements in nervous system tissues that make and use acetylcholine (ACh) as a neurotransmitter. Choline acetyltransferase (ChAT) is the enzyme catalyzing the biosynthesis of ACh and is considered to be an excellent phenotypic marker for cholinergic neurons. We have surveyed the distribution of choline acetyltransferase (ChAT)-expressing neurons in the Drosophila nervous system detected by three different but complementary techniques. Immunocytochemistry, using anti-ChAT monoclonal antibodies results in identification of neuronal processes and a few types of cell somata that contain ChAT protein. In situ hybridization using cRNA probes to ChAT messenger RNA results in identification of cell bodies transcribing the ChAT gene. X-gal staining and/or beta-galactosidase immunocytochemistry of transformed animals carrying a fusion gene composed of the regulatory DNA from the ChAT gene controlling expression of a lacZ reporter has also been useful in identifying cholinergic neurons and neural elements. The combination of these three techniques has revealed that cholinergic neurons are widespread in both the peripheral and central nervous system of this model genetic organism at all but the earliest developmental stages. Expression of ChAT is detected in a variety of peripheral sensory neurons, and in the brain neurons associated with the visual and olfactory system, as well as in neurons with unknown functions in the cortices of brain and ganglia.

Sp1/egr-like zinc-finger protein required for endoderm specification and germ-layer formation in Drosophila.

Much of our present knowledge of the biological processes involved in pattern formation in Drosophila is derived from segmentation analysis. Comparatively little is known about the genetic requirement and mechanisms underlying the formation and separation of germ layers by morphogenetic movements during gastrulation. Here we show that the Drosophila gene huckebein (hkb), a member of the gap-gene class of segmentation genes, is required for germ-layer formation at blastoderm. Absence of the hkb product, an Sp1/egr-like zinc-finger protein, causes the ectodermal and mesodermal primordia to expand at the expense of endoderm anlagen. Conversely, ectopic expression of hkb inhibits the formation of the major gastrulation fold which gives rise to the mesoderm and prevents normal segmentation in the ectoderm. Thus, hkb is necessary for endoderm development and its activity defines spatial limits within the blastoderm embryo in which the germ layers are established.