Differential expression and seasonal modulation of VGF peptides in sheep pituitary

The inducible genevgfand its peptide products are
relevant to the neuroendocrine regulation of homeostasis
and reproduction in rodents. We show here that in the
anterior pituitary of female sheep the somatotrope,
gonadotrope, and lactotrope/thyrotrope cell populations
each expressedvgfmRNA, but displayed a distinct profile
of VGF immunoreactive peptides. ProVGF C-terminus
and VGF443–588immunoreactivities were found in
lactotropes and thyrotropes, often in a subcellular location
restricted to the Golgi area and suggestive of rapid peptide
(or proVGF) release upon biosynthesis, while high
molecular weight bands consistent with proVGF were
shown in pituitary extracts. Distinct seasonal changes were
revealed, proVGF C-terminus immunoreactive cells being
largely identified as lactotropes during the summer
(83·7±2·1% (mean±S.E.M.) versus 27·0±1·9% during
the winter), as opposed to thyrotropes during the winter (73·0±1·9% versus 16·3±2·1% during the summer).
Conversely, antisera to peptides adjacent to the
VGF553–555‘Arg-Pro-Arg’ cleavage site, and to the
N-terminus of the proVGF-derived peptide V, selectively
labeled gonadotropes, indicating processing to small
peptides not retaining the proVGF C-terminus in such
cells. Finally, a peptide related to the VGF4–240region was
immunostained in somatotropes, shown in a Western blot
as a band of relative molecular mass of approximately
16 000. In conclusion, a complex, endocrine cell-typespecific
processing of proVGF was revealed. Further to the
known inducibility ofvgfmRNA upon a range of stimuli,
discreet, selective modulations of VGF-peptide profile/s
are suggested, possibly involved in specific neuro/
endocrine or modulatory mechanisms.