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Loricrin-like immunoreactivity during keratinization in lizard epidermis.

Lorenzo Alibardi1

  • 1Dipartimento di Biologia evoluzionistica sperimentale, University of Bologna, 40126, Bologna, Italy. Alibardi@biblio.cib.unibo.it

Journal of Morphology
|September 28, 2002
PubMed
Summary

This study explored whether lizard epidermis contains a loricrin-like protein, which is a key component of mammalian skin. Using X-ray microanalysis and immunocytochemical techniques, researchers examined the epidermis of the lizard Podarcis muralis. They found that small keratohyalin-like granules in alpha-keratinizing cells showed loricrin-like immunoreactivity and contained sulfur. Large granules formed from the aggregation of these small granules and also showed some loricrin-like immunoreactivity but lacked filaggrin-like properties. The study suggests that alpha keratinization in lizards resembles mammalian keratinization at the molecular level, indicating a possible evolutionary link. These findings imply that the basic mechanisms of keratin aggregation and corneous cell envelope formation may have been present in the therapsid line of reptiles, from which mammals evolved.

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Area of Science:

  • Comparative epidermal biology
  • Evolutionary developmental biology
  • Keratinocyte differentiation

Background:

The epidermis of reptiles exhibits distinct patterns of keratinization that differ from those observed in mammals. While mammalian skin forms a corneous cell envelope rich in loricrin, a sulfur-containing structural protein, reptilian epidermis has been less studied in this context. Previous research has identified two distinct keratinization processes in lizards: alpha and beta keratinization. These differ in the physical properties of the resulting corneous layers, with alpha layers being pliable and beta layers rigid. The molecular mechanisms underlying these differences remain unclear. Research has established that beta keratinization likely involves unique gene products not found in mammals. However, alpha keratinization has not been fully compared to mammalian keratinization at the molecular level. This gap motivated an investigation into whether lizard epidermis contains a loricrin-like protein, which could suggest shared evolutionary origins with mammals. Prior work has not examined the presence of loricrin in reptilian epidermis, leaving this aspect unresolved. The need to clarify the molecular basis of alpha keratinization in lizards is critical for understanding reptilian skin evolution. This uncertainty drove the current study to explore lizard epidermis for loricrin-like immunoreactivity.

Keywords:
Loricrin-like immunoreactivityLizard epidermisKeratinization mechanismsComparative epidermal biology

Frequently Asked Questions

Loricrin-like immunoreactivity suggests that lizard alpha keratinization shares molecular features with mammalian keratinization, indicating a possible evolutionary link.

Small granules contain sulfur and show loricrin-like immunoreactivity, while large granules also contain sulfur and phosphorous but lack filaggrin-like immunoreactivity.

Phosphorous is likely derived from phospholipid components within the granules, as suggested by the study's findings.

Sulfur indicates the presence of sulfur-rich proteins, such as loricrin-like molecules, in both small and large granules.

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Purpose Of The Study:

This study aimed to determine whether lizard epidermis contains a loricrin-like protein, which is a key component of the corneous cell envelope in mammals. The researchers focused on the lizard species Podarcis muralis, known for its distinct alpha and beta keratinization processes. The primary objective was to investigate the presence of loricrin-like immunoreactivity in alpha-keratinizing cells and compare it to mammalian keratinization. By examining the composition of keratohyalin-like granules in lizard epidermis, the study sought to identify structural similarities to mammalian skin. The goal was to assess whether the molecular mechanisms of keratin aggregation in lizards resemble those in mammals. This investigation could provide insights into the evolutionary conservation of epidermal differentiation. The study also aimed to explore the composition of keratohyalin-like granules and their role in forming the corneous cell envelope. Understanding these mechanisms could clarify the evolutionary relationship between reptilian and mammalian epidermis.

Main Methods:

The researchers used X-ray microanalysis to examine the elemental composition of keratohyalin-like granules in lizard epidermis. Immunocytochemical techniques were employed to detect loricrin-like and filaggrin-like immunoreactivities in alpha-keratinizing cells. Ultrastructural analysis provided detailed observations of granule morphology and distribution. The study focused on the lizard Podarcis muralis, a model species for epidermal research. Small and large keratohyalin-like granules were identified in the epidermis, particularly in the clear layer. X-ray microanalysis revealed sulfur content in these granules, suggesting the presence of sulfur-rich proteins. Immunoreactivity patterns were compared between alpha and beta keratinization layers. The presence of phosphorous and histidine in large granules was also analyzed to infer their composition.

Main Results:

The study found that small keratohyalin-like granules in alpha-keratinizing cells showed weak filaggrin-like immunoreactivity and stronger loricrin-like immunoreactivity. These granules contained sulfur, indicating a sulfur-rich protein composition. Loricrin-like immunoreactivity was detected in alpha-keratinizing layers but not in beta layers. Large keratohyalin-like granules in the clear layer formed from the aggregation of small granules and other components, including lipid material. These large granules showed some loricrin-like immunoreactivity and contained sulfur and phosphorous. Histidine was also detected in these granules, but filaggrin-like immunoreactivity was absent. Phosphorous was suggested to originate from phospholipid components within the granules. These findings indicate that alpha keratinization in lizards shares molecular features with mammalian keratinization.

Conclusions:

The findings suggest that alpha keratinization in lizard epidermis resembles mammalian keratinization at the molecular level. Loricrin-like immunoreactivity was detected in alpha-keratinizing cells but not in beta layers, indicating a distinct process. The presence of sulfur-rich granules with loricrin-like properties supports this similarity. The study also found that large keratohyalin-like granules in the clear layer contain sulfur and phosphorous but lack filaggrin-like immunoreactivity. These results imply that the basic mechanisms of keratin aggregation and corneous cell envelope formation may have been present in the therapsid line of reptiles. This suggests an evolutionary link between reptilian and mammalian epidermal differentiation. The absence of loricrin-like immunoreactivity in beta layers indicates a separate mechanism for beta keratinization. The study provides evidence that lizard epidermis may share conserved molecular features with mammalian skin.

Alpha keratinization resembles mammalian keratinization with loricrin-like immunoreactivity, while beta keratinization lacks this and involves distinct gene products.

The study suggests that the basic mechanisms of keratin aggregation may have been present in the therapsid line of reptiles, linking reptilian and mammalian epidermal differentiation.