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Deciphering the genetic programme triggering timely and spatially-regulated chitin deposition.

Moussian B, Letizia A, Martínez-Corrales G, Rotstein B, Casali A, Llimargas M - PLoS Genet. (2015)

Bottom Line: We found that Exp and Reb have interchangeable functions, and in their absence no chitin is produced, in spite of the presence of Kkv.Therefore, our results indicate that both functions are not only required but also sufficient to trigger chitin accumulation.In summary, here we identify the genetic programme that triggers the timely and spatially regulated deposition of chitin and thus provide new insights into the extracellular matrix maturation required for physiological activity.

View Article: PubMed Central - PubMed

Affiliation: Institut de Biologia Molecular de Barcelona, CSIC, Barcelona, Spain.

ABSTRACT
Organ and tissue formation requires a finely tuned temporal and spatial regulation of differentiation programmes. This is necessary to balance sufficient plasticity to undergo morphogenesis with the acquisition of the mature traits needed for physiological activity. Here we addressed this issue by analysing the deposition of the chitinous extracellular matrix of Drosophila, an essential element of the cuticle (skin) and respiratory system (tracheae) in this insect. Chitin deposition requires the activity of the chitin synthase Krotzkopf verkehrt (Kkv). Our data demonstrate that this process equally requires the activity of two other genes, namely expansion (exp) and rebuf (reb). We found that Exp and Reb have interchangeable functions, and in their absence no chitin is produced, in spite of the presence of Kkv. Conversely, when Kkv and Exp/Reb are co-expressed in the ectoderm, they promote chitin deposition, even in tissues normally devoid of this polysaccharide. Therefore, our results indicate that both functions are not only required but also sufficient to trigger chitin accumulation. We show that this mechanism is highly regulated in time and space, ensuring chitin accumulation in the correct tissues and developmental stages. Accordingly, we observed that unregulated chitin deposition disturbs morphogenesis, thus highlighting the need for tight regulation of this process. In summary, here we identify the genetic programme that triggers the timely and spatially regulated deposition of chitin and thus provide new insights into the extracellular matrix maturation required for physiological activity.

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Related in: MedlinePlus

Model of luminal chitin deposition in the trachea.(A) Kkv is present from early stages in all tracheal cells. At stage 13 Reb appears in the DT and Exp in the ventral part of the placode. Chitin accumulation starts in the DT region, where Kkv and Reb are concomitantly expressed. At early stage 14, chitin starts being deposited in regions of concomitant expression of Kkv and Exp. Exp expression progressively expands to the dorsal part of the placode, correlating with the deposition of chitin there. When Reb is expressed earlier and in all tracheal cells, chitin precociously and strongly accumulates in all branches. When Exp and Reb are missing, the presence of Kkv cannot trigger chitin deposition, and vice versa. (B) Scheme of the transcriptional regulation of kkv, exp, and reb in the trachea that ensures the timely and spatially regulated accumulation of chitin.
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pgen.1004939.g007: Model of luminal chitin deposition in the trachea.(A) Kkv is present from early stages in all tracheal cells. At stage 13 Reb appears in the DT and Exp in the ventral part of the placode. Chitin accumulation starts in the DT region, where Kkv and Reb are concomitantly expressed. At early stage 14, chitin starts being deposited in regions of concomitant expression of Kkv and Exp. Exp expression progressively expands to the dorsal part of the placode, correlating with the deposition of chitin there. When Reb is expressed earlier and in all tracheal cells, chitin precociously and strongly accumulates in all branches. When Exp and Reb are missing, the presence of Kkv cannot trigger chitin deposition, and vice versa. (B) Scheme of the transcriptional regulation of kkv, exp, and reb in the trachea that ensures the timely and spatially regulated accumulation of chitin.

Mentions: What is the functional relevance of having two genes with interchangeable roles in chitin deposition and that show partially overlapping expression? An unequivocally answer is difficult, but several lines of evidence are worth considering. On the one hand, we found that reb expression is restricted to the DT during embryogenesis, suggesting that it is required only to ensure early and strong chitin deposition in this region. This is consistent with our results, showing that in the absence of reb, DT chitin deposition is delayed and decreased, while the rest of branches and the cuticle are not affected. On the other hand our findings suggest that Reb is more efficient than Exp in performing the same function. Indeed, strong over or misexpression of reb alone or in combination with kkv generated stronger effects than when strongly overexpressing exp. In addition, in normal conditions, chitin is first deposited in branches that express reb (i.e. the DT), in spite the fact that exp is also expressed at the same time in other branches (see Fig. 7A). In contrast to reb, exp is expressed in all tracheal cells and in the rest of chitin-synthesising tissues and is required for general chitin deposition. Hence, we hypothesise that Exp is more general but less efficient at promoting chitin deposition, while Reb is more restricted but more efficient. Various explanations could be given regarding the differences in efficiency, ranging from differences at the functional level to differences in the subcellular localisation (we note that Reb apical localisation is more conspicuous than that of Exp, both in normal and overexpression conditions). In summary, Reb appears to be required only when a rapid and strong accumulation of chitin is needed. The deposition of chitin first in the DT region may represent an advantage, particularly considering that the DT does not undergo cell intercalation [27], a process that is impaired when excess chitin accumulates. Thus, the earlier and stronger accumulation of chitin in the DT may be a safety mechanism which serves to prevent cell intercalation, thereby allowing normal morphogenesis.


Deciphering the genetic programme triggering timely and spatially-regulated chitin deposition.

Moussian B, Letizia A, Martínez-Corrales G, Rotstein B, Casali A, Llimargas M - PLoS Genet. (2015)

Model of luminal chitin deposition in the trachea.(A) Kkv is present from early stages in all tracheal cells. At stage 13 Reb appears in the DT and Exp in the ventral part of the placode. Chitin accumulation starts in the DT region, where Kkv and Reb are concomitantly expressed. At early stage 14, chitin starts being deposited in regions of concomitant expression of Kkv and Exp. Exp expression progressively expands to the dorsal part of the placode, correlating with the deposition of chitin there. When Reb is expressed earlier and in all tracheal cells, chitin precociously and strongly accumulates in all branches. When Exp and Reb are missing, the presence of Kkv cannot trigger chitin deposition, and vice versa. (B) Scheme of the transcriptional regulation of kkv, exp, and reb in the trachea that ensures the timely and spatially regulated accumulation of chitin.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4305360&req=5

pgen.1004939.g007: Model of luminal chitin deposition in the trachea.(A) Kkv is present from early stages in all tracheal cells. At stage 13 Reb appears in the DT and Exp in the ventral part of the placode. Chitin accumulation starts in the DT region, where Kkv and Reb are concomitantly expressed. At early stage 14, chitin starts being deposited in regions of concomitant expression of Kkv and Exp. Exp expression progressively expands to the dorsal part of the placode, correlating with the deposition of chitin there. When Reb is expressed earlier and in all tracheal cells, chitin precociously and strongly accumulates in all branches. When Exp and Reb are missing, the presence of Kkv cannot trigger chitin deposition, and vice versa. (B) Scheme of the transcriptional regulation of kkv, exp, and reb in the trachea that ensures the timely and spatially regulated accumulation of chitin.
Mentions: What is the functional relevance of having two genes with interchangeable roles in chitin deposition and that show partially overlapping expression? An unequivocally answer is difficult, but several lines of evidence are worth considering. On the one hand, we found that reb expression is restricted to the DT during embryogenesis, suggesting that it is required only to ensure early and strong chitin deposition in this region. This is consistent with our results, showing that in the absence of reb, DT chitin deposition is delayed and decreased, while the rest of branches and the cuticle are not affected. On the other hand our findings suggest that Reb is more efficient than Exp in performing the same function. Indeed, strong over or misexpression of reb alone or in combination with kkv generated stronger effects than when strongly overexpressing exp. In addition, in normal conditions, chitin is first deposited in branches that express reb (i.e. the DT), in spite the fact that exp is also expressed at the same time in other branches (see Fig. 7A). In contrast to reb, exp is expressed in all tracheal cells and in the rest of chitin-synthesising tissues and is required for general chitin deposition. Hence, we hypothesise that Exp is more general but less efficient at promoting chitin deposition, while Reb is more restricted but more efficient. Various explanations could be given regarding the differences in efficiency, ranging from differences at the functional level to differences in the subcellular localisation (we note that Reb apical localisation is more conspicuous than that of Exp, both in normal and overexpression conditions). In summary, Reb appears to be required only when a rapid and strong accumulation of chitin is needed. The deposition of chitin first in the DT region may represent an advantage, particularly considering that the DT does not undergo cell intercalation [27], a process that is impaired when excess chitin accumulates. Thus, the earlier and stronger accumulation of chitin in the DT may be a safety mechanism which serves to prevent cell intercalation, thereby allowing normal morphogenesis.

Bottom Line: We found that Exp and Reb have interchangeable functions, and in their absence no chitin is produced, in spite of the presence of Kkv.Therefore, our results indicate that both functions are not only required but also sufficient to trigger chitin accumulation.In summary, here we identify the genetic programme that triggers the timely and spatially regulated deposition of chitin and thus provide new insights into the extracellular matrix maturation required for physiological activity.

View Article: PubMed Central - PubMed

Affiliation: Institut de Biologia Molecular de Barcelona, CSIC, Barcelona, Spain.

ABSTRACT
Organ and tissue formation requires a finely tuned temporal and spatial regulation of differentiation programmes. This is necessary to balance sufficient plasticity to undergo morphogenesis with the acquisition of the mature traits needed for physiological activity. Here we addressed this issue by analysing the deposition of the chitinous extracellular matrix of Drosophila, an essential element of the cuticle (skin) and respiratory system (tracheae) in this insect. Chitin deposition requires the activity of the chitin synthase Krotzkopf verkehrt (Kkv). Our data demonstrate that this process equally requires the activity of two other genes, namely expansion (exp) and rebuf (reb). We found that Exp and Reb have interchangeable functions, and in their absence no chitin is produced, in spite of the presence of Kkv. Conversely, when Kkv and Exp/Reb are co-expressed in the ectoderm, they promote chitin deposition, even in tissues normally devoid of this polysaccharide. Therefore, our results indicate that both functions are not only required but also sufficient to trigger chitin accumulation. We show that this mechanism is highly regulated in time and space, ensuring chitin accumulation in the correct tissues and developmental stages. Accordingly, we observed that unregulated chitin deposition disturbs morphogenesis, thus highlighting the need for tight regulation of this process. In summary, here we identify the genetic programme that triggers the timely and spatially regulated deposition of chitin and thus provide new insights into the extracellular matrix maturation required for physiological activity.

Show MeSH
Related in: MedlinePlus