Showed hyperkeratosis (Fig. 2A ), defects in the lamellar bodies of the granular cells (Fig. 2B,C), hyperproliferation (Fig. 3B) and altered of keratin marker gene expression (Fig. 3A ). The mutation was mapped using SNP analysis (Fig. 4). Molecular characterization of the Fatp4/Slc27a4 transcript (Fig. 5B) and gene (Fig. 5C) identified a point mutation in the splice donor sequence of exon 9, resulting in exon skipping during processing of the primary transcript. The altered transcript encodes a predicted truncated Fatp4 SPDP Crosslinker biological activity protein that lacks the conserved VLACS domain (Fig. 5C). Western blots confirmed the loss of expression of the fulllength protein in newborn skin (Fig. 5D). This spontaneous mutation provides further evidence that Fatp4 is essential for proper cornification and barrier formation in the epidermis. Currently, autosomal recessive congenital ichthyosis (ARCI) in humans is associated with mutations in genes including TGM1 (MIM*190195), ABCA12 (MIM *607800), ALOXE3 (MIM *607206), ALOX12B (MIM*603741), ABHD5 (MIM *604780), NIPAL4 (MIM *609383), CYP4F22 (MIM*611495), and SLC27A4/Fatp4 (MIM *604194) related to this study [38]. Among them, mutations in ABCA12, a member of the ABC transporter superfamily, cause Harlequin ichthyosis (HI), a disorder that presents at birth with a thick, tight skin that is susceptible to cracking [1]. In keratinocytes, ABCA12 is thought to regulate the transfer of glucosyl-ceramides into lamellar bodies. Loss of ABCA12 function in mice PD-1/PD-L1 inhibitor 1 causes 
hyperkeratosis (expanded stratum corneum) and malformed lamellar bodies [39]. These phenotypes resemble the “pigskin” phenotype in the Fatp4 mutant mice [10,12]. Like ABCA12, Fatp4 plays an essential role in the construction or function of lamellar bodies [10]. Fatp4 functions as an acyl-CoA synthetase with specificity towards very long chain fatty acids including arachidonate (C20:4) and lignocerate (C24:0), which are essential for lamellar bodies [4]. We therefore predict that Fatp4 and ABC12 may cooperate either directly or indirectly in lamellar bodies to help produce the normal cornified envelope (CE). Mutations of TGM1 (keratinocyte transglutaminase 1), a calcium dependent enzyme that functions in cross-linking of epidermal structural proteins and lipids into the CE, cause lamellar ichthyosis [40]. Studies have showed that expression of TGM1 is directly regulated through its promoter by GRHL3/ GET1, an epidermal-specific transcription factor [41,42]. It will be interesting to know whether GRHL3/GET1 also regulates Fatp4 expression during epidermal development. In the future, determination of the upstream regulators of Fatp4 expression and its interaction with other proteins mutated in ARCI may give us insights into the molecular events that specify the unique architecture of the CE. Recently, human mutations of FATP4 have been found to cause IPS, a well-defined congenital ichthyosis subtype [11,28?1]. Klar et al first reported FATP4 mutations in IPS patients from theAlternated Hair Follicle Growth and Skin Structure at the Earlier Stages of Pigskin EmbryosThe shiny and smooth phenotype of the newborn pigskin mutant skin and our histological studies suggested that there might be a defect in hair follicle induction, consistent with the previous report that the wrfr mutant mice had impaired hair development with fewer developing hair follicles. In mice, tylotrich or primary hair follicles (PHFs) are induced beginning at E14 and are characterized by a large.Showed hyperkeratosis (Fig. 2A ), defects in the lamellar bodies of the granular cells (Fig. 2B,C), hyperproliferation (Fig. 3B) and altered of keratin marker gene expression (Fig. 3A ). The mutation was mapped using SNP analysis (Fig. 4). Molecular characterization of the Fatp4/Slc27a4 transcript (Fig. 5B) and gene (Fig. 5C) identified a point mutation in the splice donor sequence of exon 9, resulting in exon skipping during processing of the primary transcript. The altered transcript encodes a predicted truncated Fatp4 protein that lacks the conserved VLACS domain (Fig. 5C). Western blots confirmed the loss of expression of the fulllength protein in newborn skin (Fig. 5D). This spontaneous mutation provides further evidence that Fatp4 is essential for proper cornification and barrier formation in the epidermis. Currently, autosomal recessive congenital ichthyosis (ARCI) in humans is associated with mutations in genes including TGM1 (MIM*190195), ABCA12 (MIM *607800), ALOXE3 (MIM *607206), ALOX12B (MIM*603741), ABHD5 (MIM *604780), NIPAL4 (MIM *609383), CYP4F22 (MIM*611495), and SLC27A4/Fatp4 (MIM *604194) related to this study [38]. Among them, mutations in ABCA12, a member of the ABC transporter superfamily, cause Harlequin ichthyosis (HI), a disorder that presents at birth with a thick, tight skin that is susceptible to cracking [1]. In keratinocytes, ABCA12 is thought to regulate the transfer of glucosyl-ceramides into lamellar bodies. Loss of ABCA12 function in mice causes hyperkeratosis (expanded stratum corneum) and malformed lamellar bodies [39]. These phenotypes resemble the “pigskin” phenotype in the Fatp4 mutant mice [10,12]. Like ABCA12, Fatp4 plays an essential role in the construction or function of lamellar bodies [10]. Fatp4 functions as an acyl-CoA synthetase with specificity towards very long chain fatty acids including arachidonate (C20:4) and lignocerate (C24:0), which are essential for lamellar bodies [4]. We therefore predict that Fatp4 and ABC12 may cooperate either directly or indirectly in lamellar bodies to help produce the normal cornified envelope (CE). Mutations of TGM1 (keratinocyte transglutaminase 1), a calcium dependent enzyme that functions in cross-linking of epidermal structural proteins and lipids into the CE, cause lamellar ichthyosis [40]. Studies have showed that expression of TGM1 is directly regulated through its promoter by GRHL3/ GET1, an epidermal-specific transcription factor [41,42]. It will be interesting to know whether GRHL3/GET1 also regulates Fatp4 expression during epidermal development. In the future, determination of the upstream regulators of Fatp4 expression and its interaction with other proteins mutated in ARCI may give us insights into the molecular events that specify the unique architecture of the CE. Recently, human mutations of FATP4 have been found 
to cause IPS, a well-defined congenital ichthyosis subtype [11,28?1]. Klar et al first reported FATP4 mutations in IPS patients from theAlternated Hair Follicle Growth and Skin Structure at the Earlier Stages of Pigskin EmbryosThe shiny and smooth phenotype of the newborn pigskin mutant skin and our histological studies suggested that there might be a defect in hair follicle induction, consistent with the previous report that the wrfr mutant mice had impaired hair development with fewer developing hair follicles. In mice, tylotrich or primary hair follicles (PHFs) are induced beginning at E14 and are characterized by a large.
