Btk-dependent epithelial cell rearrangements contribute to the invagination of nearby tubular structures in the posterior spiracles of Drosophila

The Drosophila respiratory system consists of two connected organs, the tracheae and the spiracles. Together they ensure the efficient delivery of air-borne oxygen to all tissues. The posterior spiracles consist internally of the spiracular chamber, an invaginated tube with filtering properties that connects the main tracheal branch to the environment, and externally of the stigmatophore, an extensible epidermal structure that covers the spiracular chamber. The primordia of both components are first specified in the plane of the epidermis and subsequently the spiracular chamber is internalized through the process of invagination accompanied by apical cell constriction. It has become clear that invagination processes do not always or only rely on apical constriction. We show here that in mutants for the src-like kinase Btk29A spiracle cells constrict apically but do not complete invagination, giving rise to shorter spiracular chambers. This defect can be rescued by using different GAL4 drivers to express Btk29A throughout the ectoderm, in cells of posterior segments only, or in the stigmatophore pointing to a non cell-autonomous role for Btk29A. Our analysis suggests that complete invagination of the spiracular chamber requires Btk29A-dependent planar cell rearrangements of adjacent non-invaginating cells of the stigmatophore. These results highlight the complex physical interactions that take place among organ components during morphogenesis, which contribute to their final form and function.     

Morphological aspects of the third instar larva of Haematobia irritans

The main morphological features of the cephalic region of the larva of Haematobia irritans (L.) are the oral grooves, tripartite labium and the antennomaxillary protuberances that have the dorsal, terminal and ventral sensory organs. The total number of sensilla that are found on the terminal organ differs from other cyclorrhaphous-fly larvae. The fan-shaped anterior spiracles usually consist of seven bulbous digits that are unequal in length. The creeping welts consist of notched, convex plates that split into two separate plates as they approach the midline of the venter. This characteristic has not been described previously for this species or other, higher, dipterous larvae. There are two posterior spiracles with an ecdysial scar, four fan-shaped and branching spiracular hairs and irregularly-shaped spiracular openings. The longitudinal anal opening is situated in the cuticular band that is known as the anal organ.     

Expression and function of the empty spiracles gene in olfactory sense organ development of Drosophila melanogaster

In Drosophila, the cephalic gap gene empty spiracles plays key roles in embryonic patterning of the peripheral and central nervous system. During postembryonic development, it is involved in the development of central olfactory circuitry in the antennal lobe of the adult. However, its possible role in the postembryonic development of peripheral olfactory sense organs has not been investigated. Here, we show that empty spiracles acts in a subset of precursors that generate the olfactory sense organs of the adult antenna. All empty spiracles-expressing precursor cells co-express the proneural gene amos and the early patterning gene lozenge. Moreover, the expression of empty spiracles in these precursor cells is dependent on both amos and lozenge. Functional analysis reveals two distinct roles of empty spiracles in the development of olfactory sense organs. Genetic interaction studies in a lozenge-sensitized background uncover a requirement of empty spiracles in the formation of trichoid and basiconic olfactory sensilla. MARCM-based clonal mutant analysis reveals an additional role during axonal targeting of olfactory sensory neurons to glomeruli within the antennal lobe. Our findings on empty spiracles action in olfactory sense organ development complement previous studies that demonstrate its requirement in olfactory interneurons and, taken together with studies on the murine homologs of empty spiracles, suggest that conserved molecular genetic programs might be responsible for the formation of both peripheral and central olfactory circuitry in insects and mammals.     

Compartments in the wing of Drosophila: A study of the engrailed gene

It has recently been suggested that the wildtype alleles of homeotic genes are responsible for controlling the development of compartments. Because the mutation engrailed gives the posterior wing compartment anterior characteristics, it can be regarded as such a homeotic gene. Our experiments confirm the role of the engrailed gene in development of the posterior wing compartment, results which strongly support and extend the compartment hypothesis.Clonal analysis reveals that the state of the engrailed gene is immaterial to the entire anterior compartment, and crucial to the normal development of the posterior compartment, where it controls the pattern of veins and bristles. The presence of a straight and precisely positioned compartment border is dependent on the activity of the engrailed gene until late in development. We suggest that this is due to the gene's effects on cell affinities of the posterior compartment.The engrailed mutation increases the size and changes the shape of the posterior compartment. engrailed clones cause local wing enlargement only if they are dorsal and include the posterior margin of the wing. Wildtype cells outside the clone contribute to this change of shape. This result suggests that the postero-dorsal margin is primarily responsible for the control of shape, and that the ventral compartment is, to some extent, modeled on the dorsal.     

虎纹捕鸟蛛体表扫描电镜观察

对虎纹捕岛蛛(Ornithoctonus husoena)的眼、生殖球、颚叶、听毛、触毛、琴形器、跗节器、发音器、幼蛛及成蛛的纺绩器和螯肢等结构进行了扫描电镜观察。     

Larval morphology of the lesser housefly, Fannia canicularis

The morphology of all larval instars of Fannia canicularis (Linnaeus) (Diptera: Fanniidae) is documented using a combination of light and scanning electron microscopy. The following structures are documented for all instars: antennal complex; maxillary palpus; facial mask; cephaloskeleton; ventral organ; anterior spiracle; Keilin's organ; posterior spiracle; fleshy processes, and anal pad. Structures reported for the first time for all instars include: two pairs of lateral prominences on the prothoracic segment; additional ventrolateral prominences on the second thoracic segment, and a papilla at the base of the posterior spiracle. Other structures reported for the first time are anterior spiracles in the first instar and a serrated tip on the mouthhook in the second instar. A trichoid sensillum on the posterior spiracular plate, representing a sensory organ otherwise unknown in the Calyptratae, is described in the second and third instars. Results are discussed and compared with existing knowledge on dipteran larval morphology.     

Respiratory significance of the thoracic and abdominal morphology of Belostoma and Ranatra (insecta,heteroptera)

Summary Both Belostoma and Ranatra possess I–II, subepimeral, thoracic subalar, and abdominal subalar air stores. In Belostoma, unlike Ranatra, the subepimeral air store is greatly enlarged, the abdominal subalar store is partially exposed to the water, and a fully exposed ventral abdominal air store is also present. All the air stores of Ranatra are normally concealed.The mesothoracic and metathoracic spiracles, which open onto the I–II and subepimeral air stores respectively, are of limited permeability. They appear to have less respiratory importance than the large and highly permeable first abdominal spiracles, which lie in the subalar air space and can probably exhale and inhale large amounts of air. The large eighth abdominal spiracles, which lie at the base of the siphon or retractile organ, can also inhale or exhale much air in Ranatra but appear to be mainly exhalant in Belostoma. The smaller second through seventh abdominal spiracles structurally resemble the eighth ones in Belostoma and open onto the ventral abdominal air store. In Ranatra they appear to have no significant respiratory function.Both genera obtain atmospheric air and give off exhaled air by means of the posterior retractile organ or siphon. The two types of air appear to follow different pathways in the two genera. In Ranatra atmospheric air appears to enter the tracheal system mainly or entirely through the eighth abdominal spiracles and then passes through the first abdominal spiracles into the subalar space. Exhaled air follows the reverse pathway. In Belostoma, however, atmospheric air probably enters the tracheae mainly through the first abdominal spiracles; it is conveyed to these spiracles from the retractile organ through the subalar space or, more indirectly, through the ventral abdominal air store. Air exhaled through the first abdominal spiracles follows the reverse route; the eighth abdominal spiracles can also exhale directly into the base of the retractile organ.During underwater respiration the abdominal portion of the subalar air store appears to be the main reservoir for oxygen. The subalar oxygen is initially atmospheric, and is supplemented, during submersion, by other sources of oxygen. Belostoma may use its exposed ventral abdominal air store, and its partially exposed abdominal subalar one, as physical gills; both these stores communicate with the inhalant first abdominal spiracles. Ranatra, none of whose air stores are normally exposed, appears, to be less capable of utilizing dissolved oxygen, but the considerable amount of atmospheric oxygen in the elongated siphon may be inhaled, during submersion, through the eighth abdominal spiracles.In both genera the thoracic air stores appear to be of less respiratory importance than the abdominal ones. They do not appear capable of obtaining large amounts of oxygen, and the thoracic spiracles are relatively impermeable. All the air stores, however, serve to protect the spiracles against the entry of water, and also contribute to the body's hydrostatic balance. It is also possible that some of the air stores play a role in pressure reception.The literature indicates much intergeneric variation in the respiration of Belostomatidae and Nepidae. In the Belostomatidae there is considerable variation in the extent of the ventral abdominal air store and in the roles of the subalar air store and the spiracles. The Nepidae show differences in their ability to utilize dissolved oxygen and in the extent of the subepimeral air store.     

Cooperation of JAK/STAT and Notch signaling in the Drosophila foregut

Temporal and spatial regulation of morphogenesis is pivotal to the formation of organs from simple epithelial tubes. In a genetic screen for novel genes controlling cell movement during posterior foregut development, we have identified and molecularly characterized two alleles of the domeless gene which encodes the Drosophila Janus kinase (JAK)/STAT receptor. We demonstrate that mutants for domeless or any other known component of the canonical JAK/STAT signaling pathway display a failure of coordinated cell movement during the development of the proventriculus, a multiply folded organ which is formed by stereotyped cell rearrangements in the posterior foregut. Whereas the JAK/STAT receptor is expressed in all proventricular precursor cells, expression of upd encoding its ligand and of STAT92E, the signal transducer of the pathway, is locally restricted to cells that invaginate during proventriculus development. We demonstrate by analyzing gene expression mediated by a model Notch response element and by studying the expression of the Notch target gene short stop, which encodes a cytoskeletal crosslinker protein, that JAK/STAT signaling is required for the activation of Notch-dependent gene expression in the foregut. Our results provide strong evidence that JAK/STAT and Notch signaling cooperate in the regulation of target genes that control epithelial morphogenesis in the foregut.     

The Hox gene Ultrabithorax modulates the shape and size of the third leg of Drosophila by influencing diverse mechanisms

The developmental mechanisms that regulate the relative size and shape of organs have remained obscure despite almost a century of interest in the problem and the fact that changes in relative size represent the dominant mode of evolutionary change. Here, I investigate how the Hox gene Ultrabithorax (Ubx) instructs the legs on the third thoracic segment of Drosophila melanogaster to develop with a different size and shape from the legs on the second thoracic segment. Through loss-of-function and gain-of-function experiments, I demonstrate that different segments of the leg, the femur and the first tarsal segment, and even different regions of the femur, regulate their size in response to Ubx expression through qualitatively different mechanisms. In some regions, Ubx acts autonomously to specify shape and size, whereas in other regions, Ubx influences size through nonautonomous mechanisms. Loss of Ubx autonomously reduces cell size in the T3 femur, but this reduction seems to be partially compensated by an increase in cell numbers, so that it is unclear what effect cell size and number directly have on femur size. Loss of Ubx has both autonomous and nonautonomous effects on cell number in different regions of the basitarsus, but again there is not a strong correlation between cell size or number and organ size. Total organ size appears to be regulated through mechanisms that operate at the level of the entire leg segment (femur or basitarsus) relatively independently of the behavior of individual subpopulations of cells within the segment.     

Whole-organ cell shape analysis reveals the developmental basis of ascidian notochord taper

Here we use in toto imaging together with computational segmentation and analysis methods to quantify the shape of every cell at multiple stages in the development of a simple organ: the notochord of the ascidian Ciona savignyi. We find that cell shape in the intercalated notochord depends strongly on anterior–posterior (AP) position, with cells in the middle of the notochord consistently wider than cells at the anterior or posterior. This morphological feature of having a tapered notochord is present in many chordates. We find that ascidian notochord taper involves three main mechanisms: Planar Cell Polarity (PCP) pathway-independent sibling cell volume asymmetries that precede notochord cell intercalation; the developmental timing of intercalation, which proceeds from the anterior and posterior towards the middle; and the differential rates of notochord cell narrowing after intercalation. A quantitative model shows how the morphology of an entire developing organ can be controlled by this small set of cellular mechanisms.     

Further studies of the engrailed phenotype in Drosophila.

Although most mutations at the engrailed locus of Drosophila cause embryonic death when homozygous, they are viable in clones of cells. We describe the phenotype of such clones in the eye-antenna, proboscis, humerus, wing, legs, and terminalia. When in anterior compartments the clones are normal, but in most posterior compartments they are abnormal and fail to respect the anteroposterior compartment boundary. We find that the yield of engrailed-lethal clones in posterior compartments is often significantly lower than expected, indicating that these clones are lost during development. Mutant clones are abnormal in the analia and rare in the humerus, suggesting that both structures are of posterior provenance. These results support the hypothesis that the engrailed+ gene is required exclusively in cells of posterior compartments to specify their characteristic cell affinities and pattern.     

Differential Delta expression underlies the diversity of sensory organ patterns among the legs of the Drosophila adult

Many studies have shown that morphological diversity among homologous animal structures is generated by the homeotic (Hox) genes. However, the mechanisms through which Hox genes specify particular morphological features are not fully understood. We have addressed this issue by investigating how diverse sensory organ patterns are formed among the legs of the Drosophila melanogaster adult. The Drosophila adult has one pair of legs on each of its three thoracic segments (the T1-T3 segments). Although homologous, legs from different segments have distinct morphological features. Our focus is on the formation of diverse patterns of small mechanosensory bristles or microchaetae (mCs) among the legs. On T2 legs, the mCs are organized into a series of longitudinal rows (L-rows) precisely positioned along the leg circumference. The L-rows are observed on all three pairs of legs, but additional and novel pattern elements are found on T1 and T3 legs. For example, at specific positions on T1 and T3 legs, some mCs are organized into transverse rows (T-rows). Our studies indicate that the T-rows on T1 and T3 legs are established as a result of Hox gene modulation of the pathway for patterning the L-row mC bristles. Our findings suggest that the Hox genes, Sex combs reduced (Scr) and Ultrabithorax (Ubx), establish differential expression of the proneural gene achaete (ac) by modifying expression of the ac prepattern regulator, Delta (Dl), in T1 and T3 legs, respectively. This study identifies Dl as a potential link between Hox genes and the sensory organ patterning hierarchy, providing insight into the connection between Hox gene function and the formation of specific morphological features.