Generation and Characterisation of Keratin 7 (K7) Knockout Mice

Aileen Sandilands,E Birgitte Lane,Kirsty M Davidson,Stewart Fleming,Frances J D Smith,Linda E Campbell,Lesley Christie,Laura D Corden,Stephanie F Maccallum,W H Irwin Mclean,Declan P Lunny

doi:10.1371/journal.pone.0064404

Abstract

Keratin 7 (K7) is a Type II member of the keratin superfamily and despite its widespread expression in different types of simple and transitional epithelia, its functional role in vivo remains elusive, in part due to the lack of any appropriate mouse models or any human diseases that are associated with KRT7 gene mutations. Using conventional gene targeting in mouse embryonic stem cells, we report here the generation and characterisation of the first K7 knockout mouse. Loss of K7 led to increased proliferation of the bladder urothelium although this was not associated with hyperplasia. K18, a presumptive type I assembly partner for K7, showed reduced expression in the bladder whereas K20, a marker of the terminally differentiated superficial urothelial cells was transcriptionally up-regulated. No other epithelia were seen to be adversely affected by the loss of K7 and western blot and immunofluorescence microscopy analysis revealed that the expression of K8, K18, K19 and K20 were not altered in the absence of K7, with the exception of the kidney where there was reduced K18 expression.

Highlights

Keratin 7 (K7) is a,55 kDa simple epithelial keratin which is primarily expressed in single-layered simple epithelia such as that found in glandular and ductal epithelia [1]
The absence of K7 protein was not associated with any pathological phenotype this is not an unexpected result given that K18 knockout mice, which show secondary loss of K7, only developed a mild late-onset phenotype that was restricted to hepatocytes with no other associated pathology [11]
Compensation for the loss of K7 by other type II keratins, in particular K8 whose expression closely overlaps with K7 [1], provides the most likely reason for the lack of any overt phenotype in K7 knockout mice but overcoming this problem of functional redundancy, through the generation of a K7/K8 double knockout mouse for example, would be difficult since both genes are closely associated within the keratin gene cluster on mouse chromosome 15 and based on previous studies embryos lacking both K7 and K8 are likely to be non-viable anyway [12,13]

Summary

Introduction

Keratin 7 (K7) is a ,55 kDa simple epithelial keratin which is primarily expressed in single-layered simple epithelia such as that found in glandular and ductal epithelia [1]. Despite the widespread diagnostic application of K7 antibodies in the field of histopathology, very little information regarding the functional role of K7 in vivo exists the lack of suitable mouse models combined with the fact that, to date, there have been no human diseases associated with mutations in the K7 gene, have all limited understanding of K7 function. Unlike the epidermal keratins, whose functions are well defined due to their association with a large number of inherited skin disorders [4], the functions of the simple epithelial keratins ie. Engineered mice, either developed through gene targeting or overexpression of mutant keratin genes, have proved to be a useful tool in helping to understand the functions of the simple keratins and the careful characterisation of these different mouse models have helped in identifying human diseases not previously associated with keratin gene mutations [6].

Methods

Results

Conclusion