Abstract :
There is no genetic disease known currently to be linked to prolactin or its receptor in goats.
Given the essential role of this hormonal system in the physiology of the mammary gland,
we reasoned that genetic anomalies of Prl/PrlR genes could be related to the occurrence of
mammary diseases. Karyotyping was performed, and the single nucleotide polymorphisms
(SNPs) of the prolactin gene were investigated in goats with gynecomastia and galactorrhea
(“milking bucks”). The results showed that the karyotype was identical between milking
bucks and normal males (2n = 60, XY). Two heterozygous SNPs, G8895A and A8898C, were
detected in exon 5 of the prolactin gene, and they corresponded to two amino acid substitutions,
lysine (Lys)→glutamate (Glu)145 and threonine (Thr)→proline (Pro)146. The first
mutation was found in only one milking buck; the second was found in both milking bucks
and in four normal males. The alignment analysis for homology of the complete coding
sequence (CDS) of the prolactin gene among cattle, sheep, goat, dog, rabbit and human
indicated that the 145th amino acid, Glu, was highly conserved in the prolactin gene of
all species that exhibited gynecomastia in males. However, the 146th amino acid was Pro
for goat, sheep, cattle and dog, and isoleucine (Ile) for rabbit and human. These mutations
occurred in the loop region, between the third and the fourth helices of prolactin, which
would affect backbone chemical shifts indirectly by changing the average chemical environment
of the backbone amides. It was presumed that the second mutation (Thr→Pro146)
may be associated with gynecomastia in bucks. Further studies are needed to confirm the
assumption.
