From bristle to brain: embryonic development of topographic projections from basiconic sensilla in the antennal nervous system of the locust Schistocerca gregaria.

The antennal flagellum of the locust S. gregaria is an articulated structure bearing a spectrum of sensilla that responds to sensory stimuli. In this study, we focus on the basiconic-type bristles as a model for sensory system development in the antenna. At the end of embryogenesis, these bristles are found at fixed locations and then on only the most distal six articulations of the antenna. They are innervated by a dendrite from a sensory cell cluster in the underlying epithelium, with each cluster directing fused axons topographically to an antennal tract running to the brain. We employ confocal imaging and immunolabeling to (a) identify mitotically active sense organ precursors for sensory cell clusters in the most distal annuli of the early embryonic antenna; (b) observe the subsequent spatial appearance of their neuronal progeny; and (c) map the spatial and temporal organization of axon projections from such clusters into the antennal tracts. We show that early in embryogenesis, proliferative precursors are localized circumferentially within discrete epithelial domains of the flagellum. Progeny first appear distally at the antennal tip and then sequentially in a proximal direction so that sensory neuron populations are distributed in an age-dependent manner along the antenna. Autotracing reveals that axon fasciculation with a tract is also sequential and reflects the location and age of the cell cluster along the most distal annuli. Cell cluster location and bristle location are therefore represented topographically and temporally within the axon profile of the tract and its projection to the brain.

Expression of specific corneous beta proteins in the developing digits of the Japanese gecko (Gekko japonicus) reveals their role in the growth of adhesive setae.

Geckos possess strong adhesion ability, even can climb on smooth surface. Previous studies have shown that the setae of geckos play a crucial role in their ability to climb on vertical walls. But the biological molecular mechanism of their adhesion ability remains unclear. In the present study, the expression patterns of corneous beta proteins (CBPs) genes related to claws, scales, and feathers development (named as ge-gprp-9, ge-gprp-10, ge-gprp-11, ge-gprp-12, ge-gprp-13, ge-gprp-14, ge-gprp-15, and ge-gprp-16 respectively) in the developing pad lamellae of different embryonic stages (stage 34, stage 36, stage 39, and stage 42) of the Japanese gecko Gekko japonicus were detected using fluorescence quantitative PCR approach. The results showed that there were significant up-regulated expression of CBPs mRNA at embryonic stage 39 with the embryonic continuous maturation and the highest expression level was detected at embryonic stage 39 or stage 42. Moreover, the expression levels of four CBPs genes ge-gprp-9, ge-gprp-10, ge-gprp-11, and ge-gprp-12 in the embryonic and adult development of gecko were detected by fluorescence in situ hybridization technique. The results from in situ hybridization detection revealed that the positive signals of these CBPs genes expression were the same in the developing pad lamellae of G. japonicus. The positive signals of eight CBPs genes were mainly found in the setae tissue, oberhautchen, and ß layer, which suggests these CBPs genes are involved in the growth of setae.

A map of sensilla and neurons in the taste system of drosophila larvae.

In Drosophila melanogaster larvae, the prime site of external taste reception is the terminal organ (TO). Though investigation on the TO's implications in taste perception has been expanding rapidly, the sensilla of the TO have been essentially unexplored. In this study, we performed a systematic anatomical and molecular analysis of the TO. We precisely define morphological types of TO sensilla taking advantage of volume electron microscopy and 3D image analysis. We corroborate the presence of five external types of sensilla: papilla, pit, spot, knob, and modified papilla. Detailed 3D analysis of their structural organization allowed a finer discrimination into subtypes. We classify three subtypes of papilla and pit sensilla, respectively, and two subtypes of knob sensilla. Further, we determine the repertoire of receptor genes for each sensillum by analyzing GAL4 driver lines of Ir, Gr, Ppk, and Trp receptor genes. We construct a map of the TO, in which the receptor genes are mapped to neurons of individual sensilla. While modified papillum and spot sensilla are not labeled by any GAL4 driver, neurons of the pit, papilla, and knob type are labeled by partially overlapping but different subsets of GAL4 driver lines of the Ir, Gr, and Ppk gene family. The results suggest that pit, papilla and knob sensilla act in contact chemosensation. However, they likely do these employing different stimulus transduction mechanisms to sense the diverse chemicals of their environment.

[Asymmetric cell division in the morphogenesis of Drosophila melanogaster macrochaetae].

Asymmetric cell division (ACD) is the basic process which creates diversity in the cells of multicellular organisms. As a result of asymmetric cell division, daughter cells acquire the ability to differentiate and specialize in a given direction, which is different from that of their parent cells and from each other. This type of division is observed in a wide range of living organisms from bacteria to vertebrates. It has been shown that the molecular-genetic control mechanism of ACD is evolutionally conservative. The proteins involved in the process of ACD in different kinds of animals have a high degree of homology. Sensory organs--setae (macrochaetae)--of Drosophila are widely used as a model system for studying the genetic control mechanisms of asymmetric division. Setae located in an orderly manner on the head and body of the fly play the role of mechanoreceptors. Each of them consists of four specialized cells--offspring of the only sensory organ precursor cell (SOPC), which differentiates from the imaginal wing disc at the larval stage of the late third age. The basic differentiation and further specialization of the daughter cells of SOPC is an asymmetric division process. In this summary, experimental data on genes and their products controlling asymmetric division of SOPC and daughter cells, and also the specialization of the latter, have been systemized. The basic mechanisms which determine the time cells enter into asymmetric mitosis and which provides the structural characteristics of the asymmetric division process--the polar distribution of protein determinants Numb and Neuralized--the orientation of the mitotic spindle in relation to these determinants, and the uneven segregation of the determinants into the daughter cells that determines the direction of their development have been discussed.