Pregnancy-Specific β-Globulin SP1

Discordant secretion of pregnancy specific beta 1-glycoprotein and human chorionic gonadotropin by human pre-embryos cultured in vitro

OBJECTIVE

To study and compare the secretion of pregnancy specific beta 1-glycoprotein (SP1) and human chorionic gonadotropin (hCG) by human pre-embryos, cultured in vitro, with their respective morphological development.

DESIGN

Spare human pre-embryos from randomly selected women participating in a program of in vitro fertilization (IVF) were studied prospectively.

SETTING

Pre-embryos were cultured, and hormone release was determined in academic research laboratories.

PATIENTS, PARTICIPANTS

Pre-embryos (n = 108) cultured for 14 days after fertilization in Ham's F-10 medium (GIBCO Ltd., Paisley, Scotland) were observed, and hCG and SP1 were measured in the culture media at regular intervals.

MAIN OUTCOME MEASURES

Discordant secretion of SP1 and hCG.

RESULTS

Of the 98 bipronucleate pre-embryos, 53.6% formed blastocysts, 17.3% of which hatched. Human chorionic gonadotropin was detected from day 7 after fertilization concomitantly with blastocyst formation, thereafter showing a logarithmic increase (maximum 10,650 mIU) until the first signs of embryonic disintegration. Pregnancy-specific beta 1-glycoprotein release started 3 to 4 days after fertilization independently of the morphological development and the future production of hCG, thereafter displaying a nonlogarithmic increase (maximum 41 ng).

CONCLUSIONS

Hormone secretion and morphological development are unique for each pre-embryo. Human chorionic gonadotropin and SP1 seem to have different biochemical and physiological regulation.

Maternal levels of pregnancy-specific beta 1-glycoprotein (SP-1) are elevated in pregnancies affected by Down's syndrome

Concentrations of pregnancy-specific beta 1-glycoprotein (SP-1) were measured in maternal blood and amniotic fluid of patients with a trisomic fetus and compared with that of a cytogenetically normal fetus at weeks 16-19 of pregnancy. The SP-1 concentrations were significantly elevated in the sera of women with a Down's syndrome fetus, whereas amniotic fluid levels were only slightly increased. It is suggested that high levels of maternal SP-1 in the second trimester of pregnancy may be a valuable indicator in the prenatal detection of fetal trisomy 21.

Heterogeneity of pregnancy-specific beta 1-glycoprotein following purification from maternal serum and partial characterization of a high-molecular-weight component

Pregnancy-Specific beta 1-Glycoprotein (PSB1G) has been purified from maternal serum by physico-chemical and immunochemical methods. Marked instability of the protein was noted after partial purification which correlated with hydroxylapatite chromatography of PSB1G. Three molecular heterogeneous forms were demonstrated by gel filtration on Sephacryl S-200 which were designated as PSB1G-I, II and III. Each of the latter purified materials displayed altered immunoelectrophoretic mobility, i.e., altered from beta 1 to gamma mobility. In immunodiffusion experiments PSB1G-I reacted in complete immunological identity with 'native' serum PSB1G whereas PSB1G-II and III reacted in partial identity with each of the latter, suggesting that they are dissociation and/or degradation products of the parent PSB1G. The apparent molecular weights of PSB1G-I, II and III as determined by gel filtration were 280 000, 69 000 and 23 000, respectively, PSB1G-I was selected for structural analysis on the basis of its immunological identity with 'native' antigen. SDS-PAGE studies of PSB1G-I with and without reducing agent strongly suggest that PSB1G-I and 'native' serum antigen are composed of two dissimilar subunits of equal molecular size which are bonded together by non-covalent linkage. One of the subunits appears to represent a single polypeptide chain, whereas the other subunit appears to be composed of two polypeptide chains of unequal size that are linked together by covalent bonds. Investigations are continuing towards confirmation of the proposed structural model of PSB1G-I by an alternate methodology of protein structure analysis.