Worm Breeder's Gazette 14(2): 47 (February 1, 1996)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

hch-1 encodes a Zn protease of the tolloid / BMP-1 family

Ryuichi Hishida¹, Takeshi Ishihara², Kazunori Kondo³, Isao Katsura⁴

hch-1 gene is necessary for two quite different developmental processes in
C. elegans: hatching and cell migration (Hedgecock et al., Development 
100:365-382, 1987). The mutant embryos cannot digest proteins in the 
eggshell and consequently show delayed hatching. hch-1 mutations also
cause the QL neuroblast and its descendants to migrate in a wrong
direction (anteriorly instead of posteriorly).

Previously we reported the isolation of a hch-1 Tc1-insertion mutation 
(ut110) and the cloning of hch-1 gene by Tc1 tagging and by transformation
rescue experiments (WBG 12(2)p.108, 13(3)p.87). We then isolated hch-1
cDNA by screening embryonic and mixed-stage cDNA libraries (kindly
provided by P. Okkema) and sequenced the longest cDNA clone. HCH-1 deduced
from this sequence data is an extracellular protein with 605 amino acids.
Data base searches revealed HCH-1 is a Zn protease related to the tolloid
/ BMP-1 family (See Figure). Members of this family are known to play
important roles in cell differentiation and morphogenesis, and several
members are thought to interact with TGF-b-like growth factors. The EGF
domain and CUB domain in those proteins are thought to act in
protein-protein interaction. The protease domain seems to process other
proteins to regulate their activity. In both amino acid sequence and
domain arrangement, HCH-1 resembles sea urchin BP10, SpAN and C. elegans
toh-1, toh-2 which were named by C. Savage et al. as a tolloid homolog
found in the data of genome sequencing project (WBG 13(4)p.64).

We investigated the expression pattern of hch-1 gene in embryos by in situ
hybridization. It was expressed in hypodermal cells at early stages of 
morphogenesis. The transcript was detectable from the time just before 
elongation (about 350 min after the first cleavage), through the comma 
stage, and until the 1.5-fold or 2-fold stages (about 430 min to 450 min).
The signal is localized first in the dorsal and lateral surface area of
the middle and posterior region of the embryos. At later stages (1.5-fold 
stage), the signal was restricted to lateral surface regions, probably 
hypodermal seam cells. These hypodermal cells have 2 faces: exterior face 
and interior face. From exterior face hatching enzymes could be secreted, 
and from interior face the proteins that control QL migration could be 
secreted. 

Our questions are as follows:
(1) Is HCH-1 a hatching enzyme? We plan to examine whether the hatching 
fluid of HCH-1 depleted with anti-HCH-1 antibodies can rescue the delayed 
hatching phenotype of hch-1 mutant embryos.
(2) What is a role of HCH-1 in QL migration? We plan to investigate 
whether hch-1 acts upstream or downstream to mab-5, which also affects QL 
migration (Salser & Kenyon, Nature 355:255-258, 1992). We will also check 
the presence and pattern of hch-1 expression in L1 larvae. It is also 
intriguing if HCH-1 forms complex with a TGF-b-like protein.
(3) Does HCH-1 have other roles in morphogenesis? The dorsal expression of
hch-1 gene at early stages of embryogenesis suggests this gene may have a 
role in morphogenesis like tolloid and BP10, which show a similar dorsal 
expression pattern in embryos. Functionally redundant genes, if any, may 
prevent hch-1 mutants to show any obvious phenotype in embryogenesis. If 
HCH-1 functions through protein-protein interaction, overexpression of a 
dominant negative hch-1 gene that has a mutation in the protease domain
may affect the morphogenesis.

Figure. Members of tolloid / BMP-1 family