PRECURSOR MATRIX PROTEINS IN THE UTERINE FLUID CHANGE WITH STAGES OF EGGSHELL FORMATION IN HENS

Organic constituents of the uterine fluid, the acellular milieu in whi ch the eggshell is mineralized, were biochemically characterized at in itial, mid and final stages of shell calcification in hens, The electr ophoretic protein profiles changed at the different stages of shell mi neralization, Two major bands (80-kDa and 43-kDa glycoproteins) with c alcium affinity were specific to the initial stage, Four protein bands of 180, 150, 116 and 32 kDa, present at the phase of rapid shell form ation, coprecipitated with calcium carbonate in vitro, At this stage w ere also present a calcium-binding glycoprotein of 36-kDa and a 20-kDa protein, Uterine fluid of the final stage was characterized by a dark er intensity of the 66-kDa band, which showed calcium-binding ability and by the presence of three additional proteins (72, 13 and 6 kDa), A t least seven bands of the uterine fluid showed similar migration patt erns to those of eggshell extracts, Western blotting with ovocleidin a nd ovalbumin antisera demonstrated the presence of these matrix protei ns in uterine fluid collected at initial and mid phase, respectively, Total uterine fluid collected at the end of calcification and dialyzed uterine fluid from the various stages delayed the rate of calcium pre cipitation in vitro, These observations demonstrate the presence of pr ecursors of eggshell matrix in the uterine fluid and support the hypot hesis of their involvement in the process of eggshell mineralization.