Targeted inactivation of the EGF and amphiregulin genes reveals distinct roles for EGF receptor ligands in mouse mammary gland development

Abstract

Targeted mice lacking functional EGF or amphiregulin (AR) were derived and bred to the TGFalpha-knockout to generate mice lacking various combinations of the three ligands. In contrast to EGF receptor (EGFR) knockout mice, triple null mice lacking half of the EGFR ligand family were healthy and fertile, indicative of overlapping or compensatory functions among EGF family members. Nevertheless, pups born to triple null dams frequently died or were runted, suggesting a mammary gland defect. Comparison of individual and combinatorial knockouts established that specific loss of AR severely stunted ductal outgrowth during puberty, consistent with dramatic expression of AR transcripts in normal developing ducts. Surprisingly, loss of all three ligands did not significantly affect cellular proliferation, apoptosis, or ERK activation within terminal end buds. Following pregnancy, most AR single null females, but few triple null females could nurse their young, revealing collaborative roles for EGF and TGFalpha in mammopoiesis and lactogenesis. In triple null glands, alveoli were poorly organized and differentiated, and milk protein gene expression was decreased. Additionally, Stat5a activation was frequently reduced in AR single and combinatorial nulls in association with impaired lactation. Collectively, our results provide genetic confirmation of a requirement for EGFR signaling throughout the development of the mouse mammary gland, and reveal stage-dependent activities for different EGFR ligands. Finally, the additional loss of growth factors from pups nursed by triple null dams further worsened their survival and growth, establishing functions for both maternal- and neonatal-derived growth factors.

Disruption of Epidermal Growth Factor Receptor but Not EGF Blocks Follicle Activation in Zebrafish Ovary

“…Surprisingly, although EGF is a well-documented growth factor involved in cell proliferation and differentiation in mammals ( Carpenter and Cohen, 1990 ; Xian, 2007 ), the loss of Egf in zebrafish did not seem to cause any major abnormalities in somatic growth and reproduction. This result agrees well with that reported in EGF null mice, which showed no overt abnormalities in growth and organ development ( Luetteke et al, 1999 ). The egf null zebrafish only exhibited minor reduction in growth rate over certain period (80–120 dpf) and reduced fertility in females after 7 mpf.…”

“…TGFα null mouse is healthy and fertile, except minor abnormalities in skin architecture and hair development ( Mann et al, 1993 ). Targeted inactivation of EGF and AREG genes severely stunts ductal outgrowth in mouse mammary glands ( Luetteke et al, 1999 ). Interestingly, all single ligand knockout mice are fertile and capable of producing live offspring ( Mann et al, 1993 ; Luetteke et al, 1999 ).…”

“…Targeted inactivation of EGF and AREG genes severely stunts ductal outgrowth in mouse mammary glands ( Luetteke et al, 1999 ). Interestingly, all single ligand knockout mice are fertile and capable of producing live offspring ( Mann et al, 1993 ; Luetteke et al, 1999 ). Disruption of EGFR gene in the mouse affects epithelial proliferation and differentiation to different degrees depending on the genetic background of the mouse strains used ( Miettinen et al, 1995 ; Sibilia and Wagner, 1995 ; Threadgill et al, 1995 ).…”

Source and Impact of the EGF Family of Ligands on Intestinal Stem Cells

“…Numerous mouse knockout studies have investigated the functional roles of individual ligands (summarized in Table 1). There is likely to be some functional redundancy given triple knockout of three of the ligands EGF, AREG, and TGFα has little effect on the intestinal epithelium with animals being viable and fertile (Luetteke et al, 1999). Similarly, single knockout of the other EGF ligands does not affect embryonic development, with the exception of Nrg1, which results in aberrant heart and neural development leading to embryonic lethality (Meyer and Birchmeier, 1995;Erickson et al, 1997).…”

“…Knockout mouse models of EGF family of ligands and receptors and their associated phenotypes.EgfEgf null mice are viable and fertile and display no overt phenotype, including in the gastrointestinal tract Luetteke et al, 1999. Areg Areg KO mice are viable and fertile and display no overt phenotype, including in the gastrointestinal tract Luetteke et al, 1999. Areg Loss of Areg significantly decreases the number of regenerating crypts following radiation-induced injury.…”