Essential Role of the Keratinocyte-Specific Endonuclease DNase1L2 in the Removal of Nuclear DNA from Hair and Nails

Abstract

Degradation of nuclear DNA is a hallmark of programmed cell death. Epidermal keratinocytes die in the course of cornification to function as the dead building blocks of the cornified layer of the epidermis, nails, and hair. Here, we investigated the mechanism and physiological function of DNA degradation during cornification in vivo. Targeted deletion of the keratinocyte-specific endonuclease DNase1-like 2 (DNase1L2) in the mouse resulted in the aberrant retention of DNA in hair and nails, as well as in epithelia of the tongue and the esophagus. In contrast to our previous studies in human keratinocytes, ablation of DNase1L2 did not compromise the cornified layer of the epidermis. Quantitative PCRs showed that the amount of nuclear DNA was dramatically increased in both hair and nails, and that mitochondrial DNA was increased in the nails of DNase1L2-deficient mice. The presence of nuclear DNA disturbed the normal arrangement of structural proteins in hair corneocytes and caused a significant decrease in the resistance of hair to mechanical stress. These data identify DNase1L2 as an essential and specific regulator of programmed cell death in skin appendages, and demonstrate that the breakdown of nuclear DNA is crucial for establishing the full mechanical stability of hair.

AKT1-mediated Lamin A/C degradation is required for nuclear degradation and normal epidermal terminal differentiation

“…Indeed, increased expression of both Dnase1L3 and 1L1 was observed. However, no change was detectable in the case of DNAse 1L2, a DNAse implicated in nuclear degradation in the epidermis, 10,11 and this result was further validated by western blot (Figure 2d). Taken together, these data suggest that the nuclear retention seen in the cornified layer in response to reduced AKT1 expression is not due to a decrease in the expression of DNAses.…”

“…The caspase-14 knockout mouse develops parakeratotic plaques upon chemical barrier disruption 8 and has subtle defects in epidermal terminal differentiation, including filaggrin processing, 9 whereas the DNAse 1L2 knockout mouse showed constitutive nuclear retention in hair and nails, which led to structural abnormalities in the hair shaft. 10,11 Parakeratosis also occurs during wound healing. 12 Nuclei are retained in the scab of healing wounds, and this correlates with the expression of different keratins and altered structural protein expression in this region.…”

Recurrent functional divergence of early tetrapod keratins in amphibian toe pads and mammalian hair

“…These keratins are not amphibian-specific innovations, but are orthologous to keratins of mammalian hair follicles and, therefore, originated in early tetrapods. In contrast to other cytoskeletal elements, keratins keep their structural backbone even when cells die [19], and leave a network of cross-linked proteins that is essential for the strength of these epidermal structures [20]. The ancestral keratins were probably already expressed in areas that required skin reinforcement in early tetrapods, and subsequently diverged to support fundamentally different adaptive structures in amphibians and mammals.…”

079 Inactivation of DNase1L2 and DNase2 in keratinocytes suppresses DNA degradation during epidermal cornification and results in constitutive parakeratosis

“…Other candidate contributors to cornification-associated DNA fragmentation include, but are not limited to, caspase-activated DNase (CAD), also known as DNA fragmentation factor B 24 and the exonuclease TREX2 10,25,26 . Like in suppression of DNA breakdown during programmed cell death of hair and nail keratinocytes 14 and sebocytes 15 , the blockade of DNA degradation by deletion of DNase1L2 and DNase2 prevented the complete removal of histone H3, a component of nucleosomes, whereas the inter-nucleosomal histone H1 and a nuclear protein without DNA interaction, lamin A/C, were degraded. Of note, the immunoreactivity of H3 was reduced in the lower but not in the upper layers of the stratum corneum in Dnase1l2 −/− Dnase2 Δep mice (Fig.…”

“…Previously, we have generated DNase1L2 knockout mice which display aberrant retention of DNA in the corneocytes of hair fibers, inner root sheaths of hair follicles, nails, tail scales, and filiform papillae of the tongue 14,15 . We have also generated Dnase2…”