Using italics in geom_text() with variables in R with ggplot2

I have some troubles with geom_text() and annotate(), respectively. First of all, I want to show the number of observations of my dot plot/barplot within the plot.
I have now solved it awkwardly via an additional vector in the dataframe where the number is stored.

library(dplyr)
library(ggplot2)  
v1 <- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2)
v2 <- c(0,0,0,0,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2)
v3 <- c(13,67,89,280,40,1,23,99,32,1,75,280,270,200,196,450,320,277,23,4,1,2,5,89,45,23,11,1,3,23,100,100,100,100,100,200,100,11,6,6,123,100,100,100,100,100,12,86,11,390,75,100,110,19,299,100,100,100,100,100,100,100,100,11,100,120,110,100,100,423,100,279,100,100,100,12,100,100,75,5,10,10,10,10,10)
v4 <- c(4,NA,NA,NA,5,NA,NA,NA,NA,NA,9,NA,NA,NA,NA,NA,NA,NA,NA,10,NA,NA,NA,NA,NA,NA,NA,NA,NA,22,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,34,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA,NA)
summary <- data.frame(v1, v2, v3, v4)
summary$v1 <- as.factor(summary$v1)
summary$v2 <- as.factor(summary$v2)
ggplot(summary, aes(x = v1, y = v3, fill = v2)) + 
geom_dotplot(binaxis  = "y", stackdir = "center", binwidth = 5, position = position_dodge(0.75), dotsize = 1) +
geom_text(aes(label = ifelse(v4>0, v4, NULL), y=500), position=position_dodge(width=0.75), vjust=-0.25, hjust=0)

Now I have a problem:

I would like to insert an "n" in italics before the number of observations (v4). I have done a lot of searching on this as well. One solution I found was substitute(paste0(italic('n='), summary$v4)), but here I get the following error:
Error in rep(yes, length.out = len) :
attempt to replicate an object of type 'language'.

If I use the following code: expression(paste0(italic('n='), summary$v4))
The "n=" is displayed in italic, but the variable is treated as text and the content of the variable is not displayed.

here an example image

Probably there is also an automatic solution how to count the number of observations automatically. Also here I would be very happy about improvements and help.

You can use parse = TRUE in geom_text

ggplot(summary, aes(x = v1, y = v3, fill = v2)) + 
  geom_dotplot(binaxis  = "y", stackdir = "center", binwidth = 5, 
               position = position_dodge(0.75), dotsize = 1) +
  geom_text(aes(label = ifelse(!is.na(v4), paste0('italic(n) == ', v4), ''), 
                y = 500), vjust = -0.25, hjust = 0, parse = TRUE,
            position = position_dodge(width = 0.75))