Normal mammary gland development after MMTV-Cre mediated conditional PAK4 gene depletion

Parisa Rabieifar,Ting Zhuang,Tânia D F Costa,Staffan Strömblad,Miao Zhao

doi:10.1038/s41598-019-50819-4

Parisa Rabieifar, Ting Zhuang + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-50819-4

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Abstract

p21-activated kinases (PAKs) are serine/threonine kinases functioning as downstream effectors of the small GTPases Rac1 and Cdc42. Members of the PAK family are overexpressed in human breast cancer, but their role in mammary gland development is not fully explored. Here we examined the functional role of PAK4 in mammary gland development by creating a mouse model of MMTV-Cre driven conditional PAK4 gene depletion in the mammary gland. The PAK4 conditional knock-out mice were born healthy, with no observed developmental deficits. Mammary gland whole-mounts revealed no defects in ductal formation or elongation of the mammary tree through the fat pad. PAK4 gene depletion also did not alter proliferation and invasion of the mammary epithelium in young virgin mice. Moreover, adult mice gave birth to healthy pups with normal body weight upon weaning. This implies that MMTV-Cre induced gene depletion of PAK4 in mice does not impair normal mammary gland development and thereby provides an in vivo model that can be explored for examination of the potential function of PAK4 in breast cancer.

Highlights

The mammary gland is a highly ductal organ mainly composed of two distinct cell compartments, the epithelium, and the surrounding stroma, which are derived from ectoderm and mesoderm during embryogenesis[1,2]
Given that complete depletion of the PAK4 gene in the mouse causes embryonic lethality[19], we created a mouse model to deplete PAK4 in the mammary epithelium using the Cre/loxP system; by crossing MMTV-Cre mice with PAK4floxed mice[20,23,24] (Fig. 1a) MMTV-Cre mice have been used in breeding, as this line has minimal effects on mammary gland development compared to other lines[23,25]
Using MMTV-Cre mediated PAK4 depletion in mammary gland epithelium, we have shown that targeted inactivation of PAK4 in mammary epithelial cells does not impair mammary gland development; this suggests that PAK4 is dispensable for murine mammary gland development and function

Summary

Introduction

The mammary gland is a highly ductal organ mainly composed of two distinct cell compartments, the epithelium, and the surrounding stroma, which are derived from ectoderm and mesoderm during embryogenesis[1,2]. Unlike most other epithelial organs, development of the mammary gland occurs postnatally[3,4] Many signaling molecules such as growth hormone, estrogen, and growth factors stimulate formation and invasion of terminal end buds (TEB) to the mammary fat pad by regulating extracellular matrix (ECM) proteins[4,5,6]. PAKs control major subcellular activities, such as cytoskeletal remodeling, mitotic progression and DNA damage response and play essential roles in organ formation throughout mammalian development[10]. Their overexpression is associated with cell proliferation, cell survival, invasion, angiogenesis and epithelial-mesenchymal transition (EMT), which are connected with cancer initiation and progression[11]. PAK4 plays an essential role during embryonic development, as complete depletion of PAK4 in www.nature.com/scientificreports/

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