What is the difference between molting and metamorphosis

The process where the exoskeleton is shed is referred to as ecdysis. It is also involved in the shedding of the epidermis and pelage. It helps different animals to adapt to various environmental changes. Metamorphosis refers to the transformation from immature to adult form through distinct stages. There are two types of metamorphosis; complete and incomplete metamorphosis. Complete metamorphosis includes four stages; egg, larva, pupa, and adult of which the stages differ greatly morphologically.

It starts with female insects laying eggs, and when they hatch to the larval stage which is typically different from the adult stage morphologically. The larval body is soft and warm-like. The larval stage shows very fast growth as it has a high appetite for food. It molts its skin several times during its growth. The third stage is the pupa, which is an inactive stage as it begins with the formation of cocoons around the larvae. Their bodies develop more segments, internal organs, wings, and legs.

A fully grown adult is finally freed from the cocoon. Of these genes, 8 genes were differentially detectable during larval molting. Some genes were known larval molting genes, such as carbA1 , irpp-inhibitor , hmg , carbA2 and a tumor necrosis factor receptor TNFR -like gene. Interestingly, these genes exhibited distinct tissue-specific expression patterns as well. For instance, carbA1 was mainly detected in molting larval fat bodies, epidermis and hemocytes, the irpp-inhibitor was mainly detected in molting larval fat bodies and epidermis, hmg was mainly expressed in molting larval midguts, carbA2 was mainly detected in molting larval epidermis; and the TNFR -like gene was mainly detected in molting larval heads, midguts and fat bodies.

An unknown EST was detectable at higher levels in all 5 tissues of molting larvae than in feeding larvae. CathL was detected at higher levels in molting larval hemocytes than feeding larval hemocytes, consistent with Northern blot analysis. The tPA gene was detected at higher levels in molting larval fat bodies compared to feeding larval fat bodies.

Some genes exhibited differential expression in different tissues during larval molting. For example, the Na-K-ATPase -like gene was detected at higher levels in the epidermis, but not in the head, midgut, or hemocytes of molting larvae. Titin appeared to be expressed at higher levels in the midgut, but not in other tissues, of molting larvae. Trypsinogen Y precursor and lipase only exhibited increased expression in molting larval fat bodies compared with other detected tissues.

Some genes did not show an obvious relationship to larval molting. For example, lbp was not differentially detected between larval molting and feeding by semi-quantitative RT-PCR, although it was detected specifically in hemocytes. Expression of the thymosin beta homologue-like gene, rpL27 and S7 were detected at almost constant levels in molting and feeding larval tissues. RpL23 and the hypothetical protein gene llacc appeared higher expression during feeding in some tissues Fig.

Three genes were differentially detected by semi-quantitative RT-PCR in a tissue-specific manner during metamorphosis. The NTF-2 was also detected at higher levels in the midgut of metamorphically committed larvae. The rpL11 was detected at higher levels during metamorphosis and in all 4 examined tissues compared with the tissues from feeding 5th larvae.

In contrast, the ecdysteroid-regulated gene was upregulated in the tissues from feeding larvae, which is consistent with the fact that it was detected in feeding 5th instar larvae by SSH Fig. Panel B gene expression during metamorphosis. Most similar genes had E-values below 0. Eleven of the putative genes were differentially detectable during larval molting or metamorphosis via semi-quantitative RT-PCR, including regulatory genes expressed during molt and metamorphosis such as NTF-2, G-proteins, and the downstream genes that may play a direct role in the molting and metamorphosis such as carbA2 and cathL.

Expression levels of these genes clearly correlated with larval molting or metamorphosis in a largely tissue-specific or developmental stage-specific manner by semi-quantitative RT-PCR analysis.

Importantly some of these genes have been reported to play a role in larval molting or metamorphosis. For examples, carbA2 has been reported to be a molting gene in Bombyx , and is expressed during molting in the epithelial tissues [ 16 ]. The CarbA2 protein has been suggested to degrade old cuticle during molting and to contribute to recycling of the amino acids in this tissue [ 16 ]. CathL , which encodes a cysteine proteinase, is involved in larval molting and cuticle and eggshell remodeling in Brugia pahangi [ 17 ].

Other genes identified in this study have not been previously known to play a role in molting or metamorphosis. Their predicted function, based on similarity, however, supports the notion that these genes participate in regulation of larval molting or metamorphosis.

For instance, nuclear transport factor-2 NTF-2 targets proteins to the nucleus in yeast and mammalian cells in culture [ 18 ]. Some genes identified in this study, based on functions of similar genes, probably participate in larval molting or metamorphosis, although they have not yet been demonstrated to be upregulated in larval molting or metamorphosis in this study.

For instance, the basic-leucine zipper gene, controls molting and metamorphosis and is likely to be involved in bZIP signaling pathways in Drosophila [ 19 ]. The basic juvenile hormone-suppressible protein 2 BJHSP2 , a juvenile hormone-sensitive protein, expresses and accumulates in the last instar larvae of Trichoplusia ni [ 20 ]. The Chk1 checkpoint protein was reported to monitor the state of DNA and can delay or arrest the cell cycle at multiple points [ 21 ]. The ribonuclease selectively attacks malignant cells, triggering an apoptotic response and inhibiting protein synthesis [ 22 ].

These putative genes represent attractive targets for further study into their functions in larval molting and metamorphosis. Ribosomal proteins have been reported to participate in various cellular processes besides protein biosynthesis.

They not only act as components of the translation apparatus, but also regulate cell proliferation and apoptosis [ 23 ].

For example, rpL11 associates with and inhibits the transcriptional activity of peroxisome proliferator-activated receptor-alpha [ 24 ]. Mitochondrial ribosomal protein L41 plays an important role in pinduced mitochondrion-dependent apoptosis by enhancing p53 stability and contributing to pinduced apoptosis [ 27 , 28 ].

RpS29 induces apoptosis in H cells [ 29 , 30 ]. RpS10 participates in both transcription and translation [ 31 ]. We detected these ribosome proteins, and they appear to be highly conserved. Among these, rpL11 was differentially expressed during metamorphosis. Whether or not other ribosome proteins participate in larval molting and metamorphosis need further study.

Interestingly, several putative immune-related genes were identified in molting larvae in this study. For instance, a lysozyme was identified in metamorphically committed larvae. Interestingly, a lysozyme has also been reported to be upregulated during larval metamorphosis in M. Other immune-related genes including the immune inducible protein and IRPP-inhibitor might play a similar role. These observations provide evidence that some immune-related genes are deferentially expressed during larval molting or metamorphosis.

We also detected an ecdysteroid-regulated protein-like gene encoding an ML domain MDrelated lipid-recognition domain in feeding 5th instar larvae. Single ML domain proteins are predicted to form a beta-rich fold containing multiple strands and to mediate diverse biological functions through interaction with specific lipids [ 33 ]. The function of this gene in larval development is unknown. In addition, three kinds of carboxypeptidase vitellogenic-like genes cpvl were detected in the epidermis of feeding 5th instar larvae.

Because these genes were detected in feeding 5th instar feeding larvae, they may play important roles in larval growth and development. Northern blot analysis indicated that some were differentially expressed during larval molting. However, RT-PCR analysis suggested that only 11 of the 22 examined genes were differentially expressed during larval molting or metamorphosis, and 4 genes, including the Na-K-ATPase-like , titin , trypsinogen Y precursor , and lipase , were only upregulated in some tissues during larval molting.

Therefore, the efficacy of SSH was not as high as indicated by the dot blot analysis. This discrepancy might be due to limitation in sensitivity of the dot blot. Intriguingly, several known genes critical for larval molting and metamorphosis in other species were not identified in this study. One possible explanation might be because that transcripts of these genes, most of them are transcription factors, are extremely rare, or they are expressed for a very short time.

Another possible explanation is that too few cDNAs were sequenced. This might be due to incomplete subtraction of the extremely highly expressed housekeeping genes or to excessive cycles of PCR amplification. According to studies in Manduca , 20E levels peak during larval molting several hours before HCS and then decrease to lower levels while JH levels peak at larval ecdysis.

After pupation, 20E peak again during pupal development [ 4 ]. Helicoverpa armigera belongs to Lepidoptera: Noctuidae and has similar 20E titer to M. The 11 differentially expressed genes detected in this study are likely regulated by the puff of 20E, which present us new gene candidates for further study the functions and regulatory expression of these genes during larval molting or metamorphosis. In addition, we present several other candidates for further studies of larval molting or metamorphosis.

These studies will extend our knowledge the regulatory mechanisms of holometabolous insect larval molting and the metamorphosis cascade. Developmental stages were defined as follows.

Fifth-0 h larvae: immediately after ecdysis with white head capsule 5th-0 h, WH. HCS lasts for about 12 h, during which larvae considered 5th instar-molting larvae 5th-molting, or 5th-HCS. Next, larvae shed their cuticle in a few minutes and enter the 6th instar 6th-0 h, WH. Sixth instar larvae eat for 48 h, then purge the gut and turn red, and begin wandering at 72 h 6th h, W-0 d. Pupae are designated P-1 d, P-2 d, and so on. According to studies in Manduca , 20E levels peak several hours before HCS and then begin to decrease.

JH levels peak at larval ecdysis. We prepared all samples for this study according to these developmental markers in individuals of equal body size. Messenger RNA was isolated from epidermis, midguts, fat bodies, hemocytes, and heads at four developmental stages using Micro mRNA Isolation kit Amersham, Uppsala, Sweden following the manufacturer's protocol. Developmental stages included the 5th to 6th instar transition, the feeding 6th instar stage 6thh , metamorphically committed larvae 6th, 96, and h , and feeding 5th instar larvae 5th h.

Three kinds of SSH were performed, including tester cDNAs from five tissues from molting 5th instar larvae and driver cDNAs from five tissues from feeding 6th instar larvae, tester cDNAs from five tissues from metamorphically committed larvae and driver cDNAs from five tissues from feeding 5th instar, and tester cDNAs from five tissues of feeding 5th instar larvae and driver cDNAs from five tissues from metamorphically committed larvae.

Figure 3: Life Stages of a Grass Hopper. The nymph resembles the adult without wings. The nymph is also smaller than the adult. The nymph eats the same food as the adult. It develops into the adult through a series of molts. It shed its exoskeleton times. When it becomes an adult, molting does not occur. Incomplete metamorphosis can be seen in termites, lice, true bugs, grasshoppers, praying mantis, crickets, and cockroaches.

Molting: Molting refers to the shed of outer body covering, feathers, hair or skin to make way for a new growth. Metamorphosis: Metamorphosis refers to the process of transformation from an immature form to an adult form through distinct life stages. Molting: Molting occurs in arthropods, amphibians, reptiles, and birds.

Metamorphosis: Metamorphosis occurs in cnidarians, insects, crustaceans, mollusks, and animals such as fish, amphibians, echinoderms and all chordates. Molting: Molting mainly refers to the shed of the exoskeleton in insects. Metamorphosis: Incomplete metamorphosis and complete metamorphosis are the two types of metamorphosis. Molting: Molting helps animals to increase the size of the body.

Metamorphosis: Metamorphosis helps to transfer from one life stage to the next. Molting and metamorphosis are two types of events in the lifecycle of animals.

Molting mainly refers to the shed of the exoskeleton in arthropods. Metamorphosis is the transformation process of the animals from an immature form to a mature form.

The main difference between molting and metamorphosis is the type of process in the above-mentioned events. Snodgrass — Fig. Figure 1: Ecdysis. View all posts.