E93-depleted adult insects preserve the prothoracic gland and molt again

ABSTRACTInsect metamorphosis originated around the middle Devonian, associated with the innovation of the final molt; this occurs after histolysis of the prothoracic gland (PG; which produces the molting hormone) in the first days of adulthood. We previously hypothesized that transcription factor E93 is crucial in the emergence of metamorphosis, because it triggers metamorphosis in extant insects. This work on the cockroach Blattella germanica reveals that E93 also plays a crucial role in the histolysis of PG, which fits the above hypothesis. Previous studies have shown that the transcription factor FTZ-F1 is essential for PG histolysis. We have found that FTZ-F1 depletion towards the end of the final nymphal instar downregulates the expression of E93, whereas E93-depleted nymphs molt to adults that retain a functional PG. Interestingly, these adults are able to molt again, which is exceptional in insects. The study of insects able to molt again in the adult stage may reveal clues about how nymphal epidermal cells definitively become adult cells, and whether it is possible to reverse this process.

E93-depleted adult insects preserve the prothoracic gland and molt again

ABSTRACTInsect metamorphosis originated around the middle Devonian, associated with the innovation of the final molt; this occurs after the histolysis of the prothoracic gland (PG; which produces the molting hormone) in the first days of adulthood. We previously hypothesized that transcription factor E93 was crucial in the emergence of metamorphosis, since it triggers metamorphosis in extant insects. This work on the cockroach Blattella germanica reveals that E93 also plays a crucial role in the histolysis of PG, which fits the above hypothesis. Previous studies have shown that the transcription factor FTZ-F1 is essential for PG histolysis. We have found that FTZ-F1 depletion, towards the end of the final nymphal instar, downregulates the expression of E93, while E93-depleted nymphs molt to adults that retain a functional PG. Interestingly, these adults are able to molt again, which is exceptional in insects. The study of insects able to molt again in the adult stage may reveal clues as to how nymphal epidermal cells definitively become adult cells, and if it is possible to revert this process.Summary statementThe prothoracic gland disintegrates after insect metamorphosis. It was believed that the factor FTZ-F1 determines this disintegration. This work reveals that FTZ-F1 action is mediated by the factor E93.

Prepatterning ofPapilio xuthuscaterpillar camouflage is controlled by three homeobox genes:clawless,abdominal-A, andAbdominal-B

Color patterns often function as camouflage to protect insects from predators. In most swallowtail butterflies, younger larvae mimic bird droppings but change their pattern to mimic their host plants during their final molt. This pattern change is determined during the early fourth instar by juvenile hormone (JH-sensitive period), but it remains unclear how the prepatterning process is controlled. UsingPapilio xuthuslarvae, we performed transcriptome comparisons to identify three camouflage pattern–associated homeobox genes [clawless,abdominal-A, andAbdominal-B(Abd-B)] that are up-regulated during the JH-sensitive period in a region-specific manner. Electroporation-mediated knockdown of each gene at the third instar caused loss or change of original fifth instar patterns, but not the fourth instar mimetic pattern, and knockdown ofAbd-Bafter the JH-sensitive period had no effect on fifth instar patterns. These results indicate the role of these genes during the JH-sensitive period and in the control of the prepatterning gene network.

Life cycle and mating behavior of Helicotylenchus multicinctus (Nematoda: Hoplolaimidae) on excised Musa cavendishii roots

The life cycle and mating behavior of Helicotylenchus multicinctus (Nematoda: Hoplolaimidae) were observed in vitro on excised roots of Musa cavendishii in gnotobiotic culture. Eggs hatched into juveniles whose appearance and structure were similar to those of the adults. Juveniles grew in size and each juvenile stage was terminated by a molt. H. multicinctus had four juvenile stages. The first molt occurred outside the egg shortly after hatching. After the final molt the juveniles differentiated into adult males and females. Mating was required for reproduction. After mating, fertilized females began to lay eggs. The life cycle from second stage juvenile to second stage juvenile was completed in 39 days.

Asynchronous maturation of the sexes may limit close inbreeding in a subsocial spider

We studied the temporal patterns of maturation and sexual receptivity of a subsocial spider, Anelosimus cf. jucundus, in southern Arizona. In subsocial spiders, sibling males and females share a common nest for a large portion of their life cycle, often only dispersing short distances close to the mating season. We found that, on average, male A. cf. jucundus matured 9 days earlier than females and that females did not become sexually receptive until 10 days following their final molt to maturity. The periods of sexual receptivity of sibling males and females, therefore, would be separated in time by a significant fraction of an adult male's life cycle. We also found significant asynchrony in maturation dates across nests and nest clusters at the two collection localities. We suggest that these temporal patterns may limit the opportunities for sibling males and females to mate with each other, thus explaining the apparent absence of mechanisms to discriminate against kin as mates in this species.

Formation of the vulva in Caenorhabditis elegans: a paradigm for organogenesis

The genes involved in the inductive interactions that specify cell fates in the vulva of Caenorhabditis elegans are known in some detail. However, little is known about the morphogenesis of this organ. Using a combination of cell biological and anatomical approaches, we have determined a complete morphogenetic pathway of cellular events that lead to the formation of the vulva. These events include reproducible cell divisions, migrations, remodeling of adherens junctions, cell fusions and muscle attachments. In the course of these events, an epithelial channel comprising a stack of 7 toroidal cells is formed that connects the internal epithelium of the uterus with the external body epithelium, forming the vulva. Vulval muscles attach to the epithelial channel and the whole structure everts during the final molt. The mature vulva has rotational, two-fold symmetry. Using laser microsurgery, we found that the two halves of the vulva develop autonomously.

The terminal differentiation factor LIN-29 is required for proper vulval morphogenesis and egg laying in Caenorhabditis elegans

Caenorhabditis elegans vulval development culminates during exit from the L4-to-adult molt with the formation of an opening through the adult hypodermis and cuticle that is used for egg laying and mating. Vulva formation requires the heterochronic gene lin-29, which triggers hypodermal cell terminal differentiation during the final molt. lin-29 mutants are unable to lay eggs or mate because no vulval opening forms; instead, a protrusion forms at the site of the vulva. We demonstrate through analysis of genetic mosaics that lin-29 is absolutely required in a small subset of lateral hypodermal seam cells, adjacent to the vulva, for wild-type vulva formation and egg laying. However, lin-29 function is not strictly limited to the lateral hypodermis. First, LIN-29 accumulates in many non-hypodermal cells with known roles in vulva formation or egg laying. Second, animals homozygous for one lin-29 allele, ga94, have the vulval defect and cannot lay eggs, despite having a terminally differentiated adult lateral hypodermis. Finally, vulval morphogenesis and egg laying requires lin-29 activity within the EMS lineage, a lineage that does not generate hypodermal cells.

The heterochronic gene lin-29 encodes a zinc finger protein that controls a terminal differentiation event in Caenorhabditis elegans

A hierarchy of heterochronic genes, lin-4, lin-14, lin-28 and lin-29, temporally restricts terminal differentiation of Caenorhabditis elegans hypodermal seam cells to the final molt. This terminal differentiation event involves cell cycle exit, cell fusion and the differential regulation of genes expressed in the larval versus adult hypodermis. lin-29 is the most downstream gene in the developmental timing pathway and thus it is the most direct known regulator of these diverse processes. We show that lin-29 encodes a protein with five zinc fingers of the (Cys)2-(His)2 class and thus likely controls these processes by regulating transcription in a stage-specific manner. Consistent with this role, a lin-29 fusion protein binds in vitro to the 5′ regulatory sequences necessary in vivo for expression of col-19, a collagen gene expressed in the adult hypodermis. lin-29 mRNA is detected in the first larval stage and increases in abundance through subsequent larval stages until the final molt, when lin-29 activity is required for terminal differentiation.

The ecology of Taeniopteryx nivalis (Fitch) (Taeniopterygidae; Plecoptera) in a small stream in southern Ontario

Taeniopteryx nivalis (Fitch) has a simple, univoltine life cycle in a southern Ontario stream. Emergence occurs in March, the adults live for about 1 month and the eggs are laid 1–3 weeks after the main emergence in batches of 200–600. Mating and oviposition were observed in the laboratory, and the eggs and hatchlings are described. The eggs begin to hatch in late April to mid-June in the field and the nymphs probably undergo diapause in instar 4 from July to late September. An attempt to collect diapausing nymphs in the field is discussed. Diapause is broken in late September to mid-October and growth proceeds rapidly initially but tapers off through the penultimate and final instars. The final molt takes place in late December to mid-January. There are 9 postdiapause instars for a total instar number of 13. The nymphs feed on detritus and continue to feed until shortly before emergence. Some of the difficulties of using indirect methods of determining instar number are discussed.

Ontogeny of phonotaxis in Orchelimum gladiator (Orthoptera: Tettigoniidae: Conocephalinae)

The ontogeny of phonotaxis in female Orchelimum gladiator was monitored in a circular arena using attraction to tape-recorded conspecific male song as the response criterion. Parasite-free females became responsive on day 5 or 6 after the final molt. Response appeared to wane after the 9th day. Mating on the 15th day extinguished responsiveness. Nematomorph-parasitized females were generally less responsive to song and none mated even when placed with a male.