Identification of reptilian genes encoding hair keratin-like proteins suggests a new scenario for the evolutionary origin of hair

Eckhart, Leopold; Valle, Luisa Dalla; Jaeger, Karin; Ballaun, Claudia; Szabo, Sandra; Nardi, Alessia; Buchberger, Maria; Hermann, Marcela; Alibardi, Lorenzo; Tschachler, Erwin

doi:10.1073/pnas.0805154105

Cited by 108 publications

(137 citation statements)

References 32 publications

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“…1C and Table 1). Recent studies have shown that the latter seems to represent the most primitive type II hair keratin as K84 homologues have been detected in the claws of lizards (17). Remarkably, but compatible with its position in the phylogenetic tree, the non-␣-helical domains of the K80 neighbor K78 (Fig.…”

Section: Discussionmentioning

confidence: 55%

Against the Rules: Human Keratin K80

Langbein

Eckhart

Rogers

et al. 2010

Journal of Biological Chemistry

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Of the 54 human keratins, five members have, at present, only been characterized at the gene level. In this study we have investigated the expression patterns of keratin K80, whose gene is located at the centromeric end of the type II keratin gene domain. K80 possesses a number of highly unusual properties. Structurally, it is distinctly closer to type II hair keratins than to type II epithelial keratins. Nonetheless, it is found in virtually all types of epithelia (stratified keratinizing/non-keratinizing, hard-keratinizing, as well as non-stratified tissues, and cell cultures thereof). This conspicuously broad expression range implies an unprecedented in vivo promiscuity of K80, which involves more than 20 different type I partners for intermediate filament (IF) formation. Throughout, K80 expression is related to advanced tissue or cell differentiation. However, instead of being part of the cytoplasmic IF network, K80 containing IFs are located at the cell margins close to the desmosomal plaques, where they are tightly interlaced with the cytoplasmic IF bundles abutting there. In contrast, in cells entering terminal differentiation, K80 adopts the "conventional" cytoplasmic distribution. In evolutionary terms, K80 is one of the oldest keratins, demonstrable down to fish. In addition, KRT80 mRNA is subject to alternative splicing. Besides K80, we describe a smaller but fully functional splice variant K80.1, which arose only during mammalian evolution. Remarkably, unlike the widely expressed K80, the expression of K80.1 is restricted to soft and hard keratinizing epithelial structures of the hair follicle and the filiform tongue papilla.At present, of the 54 human keratins, only five members, i.e. the type I keratins K23, K24, and the type II keratins K78, K79, and K80 (1-3), have been characterized essentially at the gene/cDNA level, whereas detailed studies on the expression of the respective mRNAs and their proteins in human epithelia are still missing. To close this gap, we set out to investigate the expression characteristics of the type II keratin K80 (previously designated Kb20 (4)). Earlier bioinformatic analyses have shown that the KRT80 gene is located at the centromeric end of the human type II keratin gene domain on chromosome 12q13.13 (Fig. 1A). The isolated K80 cDNA encodes a 452-amino acid protein with a calculated molecular mass of 50.5 kDa and an isoelectric point of 5.47 (2).Remarkably, ␣-helical rod domain-based evolutionary analyses of the 26 type II keratins revealed a conspicuously long branch length for K80, thus indicating a relatively low homology of its ␣-helix to those of the remaining type II epithelial keratins, whereas its sequence affinity to type II hair keratins was relatively high (Fig. 1B, and Ref. 2). This was also reflected in the non-␣-helical K80 end domains that contained a relatively high number of proline and cysteine residues along with the complete absence of GGG or GGX repeats (2), typically found in the head and tail domains of most type II epithelial keratins (Fig....

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Section: Discussionmentioning

confidence: 55%

Against the Rules: Human Keratin K80

Langbein

Eckhart

Rogers

et al. 2010

Journal of Biological Chemistry

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“…[11][12][13] Our recent studies have suggested that SFTPs originated prior to the diversification of amniotes (mammals, reptiles and birds). [14][15][16] However, the evolutionary origin of SFTPs has remained uncertain because of incomplete genome data of the next relatives of amniotes, the amphibians.…”

Section: Questions Addressedmentioning

confidence: 99%

Filaggrin has evolved from an “S100 fused‐type protein” (SFTP) gene present in a common ancestor of amphibians and mammals

Mlitz

Hussain

Tschachler

et al. 2017

Experimental Dermatology

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The expression of filaggrin in differentiated keratinocytes and the association of filaggrin mutations with ichthyosis vulgaris and atopic dermatitis suggest that this prototypical member of the S100 fusedtype protein (SFTP) family plays a key role in the epidermal barrier to the environment. Here, we report that SFTP genes are present not only in amniotes but also in amphibians. Four SFTPs are expressed in the skin of the frog Xenopus laevis. The results of this study indicate that filaggrin has evolved from an ancestral SFTP that may have contributed to skin modifications during the evolutionary transition to terrestrial life.

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“…Although these fractions were determined on a keratins (Alexander & Earland 1950;Gillespie et al 1968;Lindley & Cranston 1974), we believed, as implied by some workers (Wainwright et al 1976), that the fractions might be similar in b keratins. We mention in parentheses subsequent research (Eckhart et al 2008) that shows that cysteine-rich a keratins are not restricted to mammals and that the evolution of mammalian hair may have involved the cooption of pre-existing structural proteins (lizards and birds) and, interestingly, that in the keratins in lizard claws there were sulphur -sulphur bonds unrelated to mammalian counterparts.…”

Section: Introductionmentioning

confidence: 99%

Selective biodegradation of keratin matrix in feather rachis reveals classic bioengineering

2009

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Flight necessitates that the feather rachis is extremely tough and light. Yet, the crucial filamentous hierarchy of the rachis is unknown-study hindered by the tight chemical bonding between the filaments and matrix. We used novel microbial biodegradation to delineate the fibres of the rachidial cortex in situ. It revealed the thickest keratin filaments known to date (factor .10), approximately 6 mm thick, extending predominantly axially but with a small outer circumferential component. Near-periodic thickened nodes of the fibres are staggered with those in adjacent fibres in two-and three-dimensional planes, creating a fibre-matrix texture with high attributes for crack stopping and resistance to transverse cutting. Close association of the fibre layer with the underlying 'spongy' medulloid pith indicates the potential for higher buckling loads and greater elastic recoil. Strikingly, the fibres are similar in dimensions and form to the free filaments of the feather vane and plumulaceous and embryonic down, the syncitial barbules, but, identified for the first time in 140þ years of study in a new location-as a major structural component of the rachis. Early in feather evolution, syncitial barbules were consolidated in a robust central rachis, definitively characterizing the avian lineage of keratin.

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Identification of reptilian genes encoding hair keratin-like proteins suggests a new scenario for the evolutionary origin of hair

Cited by 108 publications

References 32 publications

Against the Rules: Human Keratin K80

Against the Rules: Human Keratin K80

Filaggrin has evolved from an “S100 fused‐type protein” (SFTP) gene present in a common ancestor of amphibians and mammals

Selective biodegradation of keratin matrix in feather rachis reveals classic bioengineering

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