Errors in corticospinal axon guidance in mice lacking the neural cell adhesion molecule L1.

BACKGROUND: Neural cell adhesion molecules of the immunoglobulin superfamily (IgCAMs) have been implicated in both the fasciculation and guidance of axons, but direct genetic evidence of a role for neural IgCAMs in axon guidance in vertebrates is lacking. The L1 subfamily of vertebrate neural IgCAMs function as both homophilic and heterophilic receptors for a variety of cell-surface and extracellular ligands and may signal through intracellular kinases or by recruitment of the fibroblast growth factor receptor. L1 itself has been implicated in many neural processes and is expressed widely in the embryonic and adult nervous systems. In humans, mutations in the L1 gene are linked with a spectrum of brain disorders, including loss of the corticospinal tract, but the mechanistic basis for these disorders is unknown. RESULTS: We show that mice that do not express L1 have defects in the guidance of axons of the corticospinal tract, a major motor control pathway projecting from the cortex to the spinal cord. Although the pathway to the caudal medulla appears normal, a substantial proportion of axons fail to cross the midline to the opposite dorsal column as normal. In adults, this results in a reduced decussation and in large numbers of axons projecting ipsilaterally. There is also a varying, but reduced, number of corticospinal axons in the dorsal columns of the spinal cord. These do not project beyond cervical levels. We show that these are defects in axon guidance, because they arise during the early stages of the development of the decussation. The presence of a ligand for L1, CD24, specifically at the point of decussation suggests a mechanism in which L1 functions to guide corticospinal axons across the midline. CONCLUSIONS: L1 function is necessary for the guidance of corticospinal axons across the pyramidal decussation in mice. Some of the defects in the corticospinal tract of humans with mutations in L1 could be due to errors in axon guidance at the pyramidal decussation.

Selective use of leuprolide acetate in women undergoing superovulation with intrauterine insemination results in significant improvement in pregnancy outcome.

OBJECTIVE: To examine the incidence of premature luteinization in individuals undergoing hMG with IUI therapy, the association between premature luteinization, cycle fecundity, and pregnancy outcome, and to determine if the selective use of leuprolide acetate (LA) in women demonstrating premature luteinization improves pregnancy outcome in subsequent hMG with IUI cycles. DESIGN AND SETTING: Retrospective analysis of superovulation cycles from January 1990 until December 1991 at the University of Connecticut Health Center. PATIENTS: All women with ovulatory function undergoing hMG superovulation with IUI. INTERVENTIONS: All patients were tested for evidence of premature luteinization. Those demonstrating premature luteinization were started on LA in the luteal phase in their subsequent hMG with IUI cycle. MAIN OUTCOME MEASURES: Peak serum E2, the number of mature preovulatory follicles, the number of ampules of hMG, days of hMG therapy, cycle fecundity, and spontaneous abortion rate. RESULTS: Thirty-three percent of all hMG with IUI patients showed evidence of premature luteinization, with premature luteinization occurring in 22.2% of conception cycles and 37.4% of nonconception cycles. For those women who demonstrated premature luteinization in their conception cycle, 90.0% of the pregnancies ended with either spontaneous abortion or were biochemical in nature compared with 44.3% in the cycles without evidence of premature luteinization. Cycle fecundity was 11.1% in patients demonstrating premature luteinization compared with 26.3% for patients without premature luteinization. All women demonstrating premature luteinization and not conceiving were placed on LA in the luteal phase and had a subsequent cycle fecundity of 18.9% with the percent pregnancy wastage being significantly less (33.3% versus 90.0%) when LA was used. CONCLUSIONS: Premature luteinization is a common occurrence during hMG therapy and is associated with decreased cycle fecundity and an increased incidence of spontaneous abortion and biochemical pregnancies. The selective use of LA in those individuals demonstrating premature luteinization results in a significant increase in the percent of women conceiving a viable pregnancy.

The value of increasing the dose of human menopausal gonadotropins in women who initially demonstrate a poor response.

OBJECTIVE: To evaluate the benefit of increasing the hMG dose in subsequent superovulation cycles for those individuals who demonstrate a poor response on up to three ampules of hMG daily. DESIGN AND SETTING: Retrospective analysis of all superovulation cycles at the University of Connecticut Health Center. PATIENTS: All women undergoing hMG therapy with IUI from January 1990 until December 1992. INTERVENTIONS: All patients were initially stimulated with up to three ampules of hMG daily. All patients who did not conceive on their first hMG cycle and demonstrated a poor response to hMG therapy were started on higher doses of hMG in an effort to obtain a good response. A maximum of eight ampules of hMG per day were used. MAIN OUTCOME MEASURES: Peak serum E2, the number of mature preovulatory follicles, and cycle fecundity were compared. RESULTS: The poor responders using up to three ampules daily had a peak E2 of 384 +/- 26 pg/mL (1,421 +/- 96 pmol/L), 1.4 +/- 0.1 mature follicles, and a cycle fecundity of 3.1% compared with an E2 of 900 +/- 83 pg/mL (3,330 +/- 307 pmol/L), 2.7 +/- 0.2 mature follicles, and a cycle fecundity of 4.3% when these poor responders had their dose increased to five or more ampules daily. Those individuals demonstrating a good response on less than or equal to three ampules of hMG daily had an average peak E2 of 1,159 +/- 41 pg/mL (4,288 +/- 151 pmol/L), 3.4 +/- 0.2 mature follicles, and a cycle fecundity of 16.5%. CONCLUSIONS: Despite significant improvement in peak E2 and the number of mature preovulatory follicles when the hMG dose was increased in poor responders, no significant increase in cycle fecundity was noted.

The "lecithotrophic" sea urchin Heliocidaris erythrogramma lacks typical yolk platelets and yolk glycoproteins.

The sea urchin Heliocidaris tuberculata undergoes typical development, forming an echinoid pluteus larva, whereas H. erythrogramma undergoes direct development via a highly modified, nonfeeding larva. Using a polyclonal antibody prepared against yolk glycoproteins from the typical developer Stronglyocentrotus purpuratus, we found that H. tuberculata contains cross-reactive proteins in abundance, but H. erythrogramma does not. In addition, we used immunoelectron microscopy to demonstrate that unfertilized eggs of H. tuberculata contain yolk platelets, but those of H. erythrogramma do not.

Loss of yolk platelets and yolk glycoproteins during larval development of the sea urchin embryo.

The fate of the yolk platelets and their constituent yolk glycoproteins was studied in Strongylocentrotus purpuratus eggs and embryos cultured through the larval stage. Previous studies have shown that the yolk glycoproteins undergo limited proteolysis during early embryonic development. We present evidence that the yolk glycoproteins stored in the yolk platelets exist as large, disulfide-linked complexes that are maintained even after limited proteolysis have occurred. We provide additional evidence that acidification of the yolk platelet may activate a latent thiol protease in the yolk platelet that is capable of correctly processing the major yolk glycoprotein into the smaller yolk glycoproteins. Because we previously showed that these yolk glycoproteins are not catabolized during early embryonic development, it was of interest to study their fate during larval development. Using a specific polyclonal antibody to a yolk glycoprotein, we found that both yolk glycoproteins and the yolk platelets disappeared in feeding, Day 7, larval stage embryos, but that starvation did not significantly affect the levels of the yolk glycoproteins. We also found that the yolk glycoproteins reappeared in 30-day-old premetamorphosis larvae.

Structure of a major yolk glycoprotein and its processing pathway by limited proteolysis are conserved in echinoids.

To study the fate of the yolk glycoproteins found in eggs and embryos of the sea urchin, Strongylocentrotus purpuratus, a polyclonal antibody to a 90-kDa polymannose glycoprotein found in the embryo was prepared. Immunoblot analysis of total proteins over the course of development showed that this antibody recognized a family of glycoproteins. Concomitant with the disappearance of the major 160-kDa yolk glycoprotein of the egg during embryogenesis, glycoproteins with a lower molecular mass appeared. These glycoproteins (115, 108, 90, 83, and 68 kDa) were purified from S. purpuratus and analyzed by limited proteolysis and peptide mapping. This analysis revealed that these glycoproteins were cleavage products derived from the major yolk glycoprotein. The antibody to the 90-kDa glycoprotein in S. purpuratus embryos was used to identify a homologous set of yolk glycoproteins with similar molecular masses in the embryos of three other species in the class Echinoidea: Arbacia punctulata, Lytechinus pictus, and Dendraster excentricus. However, eggs from other echinoderm classes and from Xenopus laevis, Drosophila melanogaster, and the chicken did not contain any cross-reactive molecules. Cross-reactivity within the class Echinoidea was not due to a common carbohydrate epitope, because the antibody recognized the glycoproteins even after the N-linked carbohydrate side chains were enzymatically removed. The major yolk glycoprotein (160-170 kDa) from each of the three sea urchin species was purified and analyzed. Comparison of the physical and chemical properties of these glycoproteins revealed striking similarities in pI and in amino acid and monosaccharide composition. The results of peptide mapping also supported the conclusion that the 160- to 170-kDa glycoproteins from the four echinoids are structurally homologous glycoproteins containing N-linked polymannose chains. Immunolocalization by electron microscopy in S. purpuratus showed that the yolk glycoproteins remained within the yolk platelet throughout development, and that externalization of the 160-kDa glycoprotein or its cleavage products was not detectable.